integration of climate change considerations in hydropower developments adaptations and policy...
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Integration of Climate Change Considerations in Hydropower Developments‐Adaptations and Policy
Recommendation
Final Report
Submitted to: Government of Nepal
Ministry of Environment, Science and Technology
Kathmandu, Nepal
Submitted by: The Society of Hydrologists and Meteorologists (SOHAM) Nepal
Kathmandu, Nepal
Email: [email protected];[email protected]
June 2012
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Acknowledgement Hydropower development of Nepal in the Context of Climate Change is an attempt to show impacts of climate change on one of the important sector of water resource.
Water is a key element to hydropower development. Climate change impacts on it need to be handled carefully and skillfully. The report is intended to present scenario of the impacts of climate change on river flows which is though challenging because water availability, quality of stream flow is sensitive to temperature and precipitation.
South Asia is particularly more vulnerable to its impacts and some of the impacts already seen in Nepal in the form of drought, downstream flooding, intense rainfall, shifting of monsoon period. Nepal is suffering from either too much water or too little water to sustain life due to climate change.
Climate change impacts on hydropower development may be addressed by focusing on research, optimum observation network, strong database, adaptation and mitigation techniques. This report is an effort to bring some important issues of climate change to readers and building a strategy to cope with its impacts.
I would like to express warm appreciation and thanks to Mrs. Kalpana Dhamala, Ex. Minister, Ministry of Science and Technology, and Mr. Suresh Marahatta, advisor to the Minister. I would also like to thank to Secretary, Ministry of Science and Technology, Director General, Department of Hydrology and Meteorology and to all executive members of SOHAM‐Nepal
Society of Hydrologists and Meteorologists, Nepal
(SOHAM Nepal)
Kathmandu
June, 2012
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Research Team
Mr. Jagat Kumar Bhusal : Team Leader of the Study
Mr. Deepak Paudel
Mr. Santosh Regmi
Mrs. Indiral Kandel
Mr. Binod Parajuli
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Executive Summary
The Himalayan glaciers hold the largest store of fresh water outside the Polar Ice Caps. Many of the rivers on the Asian continent originate in the Himalayas. Steady glacial melt has fed these rivers, regulating their flow throughout the annual hydrological cycle. But many of these glaciers are rapidly melting, causing yet more volatility in the flow levels of rivers in Asia.
Nepal contains about two percent of the world’s water resources. There are more than 6000 rivers in Nepal out of which about 54 rivers are each longer than 150 kilometres and 964 rivers are each longer than 10 kilometres (DHM,1998) These river in total posses an appreciable of hydroelectricity which is more than 83 thousand (Shrestha, H M). Power of water been used since ancient times to grind flour and perform other tasks. In 1878 the world's first hydroelectric power scheme was developed at Crag side in Northumberland of England by William George Armstrong. The first hydropower electricity project (Pharping hydroporoject) of 500‐kilowatt capacity. was installed in 1911 in Nepal. Till date, total installed capacity is 700 MW out of which 174 MW fall under private sectors. Karnali, Chisapani location is identified for a Multipurpose Project with an installed capacity of 10,800 MW.
Deglaciation in the Himalaya will also cause rapid growth of glacial lakes, which will increase the likelihood of glacial lake outburst floods. The deglaciation pattern will deliver water to the rivers in sporadic bursts rather than a steady stream of flow. These devastating and often unexpected floods could wreak havoc on hydroelectric infrastructure. Glacial melt will cause initial overall increased flow for the rivers originating in the Himalaya. However, highly variable river flow is not optimal for hydropower, so even though deglaciation will increase the flows at certain periods of time, its variability and unpredictability make hydropower more vulnerable on rivers. Some smaller rivers are fed exclusively by glacial melt, and could dry up in as few as 50 years. This naturally would affect downstream hydropower, not to mention the water supply of communities along such rivers.
Various scientific studies’ results and information from multiple sources that are focused on climate change vulnerability to water resource, especial focus on hydropower are synthesized and integrated. Stream flow is an important parameter of a hydroelectric generation by which installed capacity and energy output is determined. Climate change which has impacted precipitation patterns, glacial melting has been altering the stream flows and also have impacted on seasonal variation and annual fluctuation in flows. Run‐of‐river type of hydroelectric project is likely to be affected because they lack storage facilities to buffer fluctuations in water flow. The storage type partially blocks the water flow of a river and store water upstream of the dam to create a reservoir. Stored water in the reservoir is used to produce electricity at desired time.
To understand how climate change will affect hydropower production, it is necessary to consider the ways in which characteristics of hydropower facilities affect their vulnerability to climate change.
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Changes in temperature and changes in precipitation patterns have profound effects on river systems. Evaporation, discharge, temporal variability, and glacial melt impact the vulnerability of certain hydropower facilities and reservoir characteristics. Planned projects should take reservoir shape into consideration in their design in order to reduce evaporation and maximize power potential(McJannet et al, 2008).. Reservoir size is important to evaporation as well, as smaller reservoirs will be more at risk to losing greater proportions of their volume.
The inherent characteristic of climate is that it changes with time. The degree of climate variability that is described by the differences between long‐term statistics of meteorological elements calculated for different periods is the measure of climate change.
The last glaciation, which occurred at about 10000 calendar years before present. The climate during the Holocene period appeared relatively stable but there were significant climate fluctuations during this period (e.g. Bond et al. 1997; Mayewski et al. 1997; deMenocal et al. 2000). However the significant cause of the warming trend is seen as the ‘Greenhouse Effect’ – a well‐understood phenomenon that was discovered in 1824 and first measured in 1859 (IPCC Assessment Report 4, 2007).The major greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N20). Some concentrations of GHGs in the atmosphere are natural but human activity is producing more and more of these gases each year. Eleven of the 12 years from 1995 to 2006 are among the 12 warmest years on record (IPCC AR4 WGI). Indeed, the 10 warmest years from the UK Meteorological Office’s 160‐year records are all since 1997, while eight of them are after 2001. (UK Met Office HadCRUT3 temperature record).
Climate change will cause increased temporal variability of precipitation events. This will pose significant problems for hydroelectric generation. These impacts will result in more severe and frequent floods and droughts. Seasonal offsets, or the altering timing and magnitude of precipitation for traditional rainy and dry seasons and peak snowmelt, will occur as well (Izrael, Y. 2007). The magnitude of climate change induced precipitation shifts will vary greatly by season. In some cases precipitation is projected to be reduced twice as much in one season while in other regions, wet seasons may become drier and the dry seasons may become wetter (Harrison, G. P., & Whittington, H., 2002)
Regional findings provided a preliminary basis for collecting information that climate change impacts will most significantly impact hydropower generation across the globe. A type of dam characteristics determines affects on them by types of climate change impacts. The other factors determining the responses to climate change impacts on hydropower generation are political, social and economic factors, unique to the region.
One study in the Peribonka River watershed in Quebec, Canada predicted mean annual hydropower to decrease by 1.8 percent between 2010‐2039 due to initial early peak flows and lack of summer precipitation) and subsequently increase by 9.3 percent and 18.3 percent during 2040‐2069 and 2070‐2099 respectively due to steadily increasing precipitation amounts (Minville et al, 2009). Some predictions forecast a 40 percent loss in production by 2080 in the Pacific Northwest of the United States. The prediction in increasing temperature and decreasing in rainfall hinted to likely a negative effect on mean annual discharge, and in hydroelectric production. Earlier snowmelts will shift seasonal
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peak flow time thereby hurting hydroelectric production, especially during the summer when it’s needed most (Power Markets Week, 2005)
In south and southeastern Europe, likelihood of droughts is increased and decrease in precipitation that will lead to reduced water availability in 2070. So there will decline in hydropower production correspondingly about 20 to 50 percent in counties like, Portugal, Spain, Ukraine, and Bulgaria (Lehner et al. 2005). In the short‐term, glacially fed rivers, such as those originating in the Alps and Pyrenees, will likely see increases in summer discharge as glaciers melt faster than they regenerate. Already, rivers in the Alps are seeing 13 percent increases in flow in August compared to two decades ago, and many glaciers have diminished significantly (Huss, M, 2011). In the long‐term, the contribution of these retreating glaciers to river flow will decrease, by 15 to 45 percent by the end of this century (Lehner et al. 2005). Overall across Europe, developed hydropower potential is predicted to decrease 7 to 12 percent by the year 2070 (Lehner et al, 2005). These decreases must also be considered within a broader context of increased water and electricity usage.
In Congo River Basin, Harrison and Whittington. (2002) have noted that “Simulations indicate that for all scenarios annual flow levels at Victoria Falls reduce between 10 and 35.5 percent. In each case the resultant flow change is greater than the precipitation change, confirming the amplifying effect of the hydrology.”
Spatial variation of the annual mean temperature trend analysis showed the increasing trend in almost entire country except on few isolated places. No perfect trend is established till date and outcomes vary. The IPCC AR4 has indicated that the warming in South Asia would be at least 2–4 degree Celsius by the end of the century (Christensen et al. 2007). The warming rates follow the elevational gradient in the Himalayan region (e.g.,Bhutan, Nepal, and Himachal Pradesh). Trend analysis on observed data rainfall and temperature was performed
The mean temperature over Nepal has a rising trend by about 0.02 to .06 per year ( Shrestha et al, 1999, Karmacharya etal, 2007, Baidya etal, 2008, Practical Action 2009). The average annual rainfalls in the basin and on overall western regions of Nepal have a positive trend (Baidya etal, 2008). Nepal may get warming on average by 3.5–4 degree Celsius in those scenarios at the end of the century. Annual rate of temperature rise was found to be about 0.41o C per decade. Trend on precipitation was decreasing at the rate of 9.8mm/decade in the month of April and May though, a rising trend of precipitation was observed during monsoon seasons. Trends of monsoon onset and withdrawal from 21 years of data show that monsoon season is elongating in both the ends. Onset will occur earlier by 71 % of a day per annum and withdrawal will retreat by about 15 % of a day per annum.
Precipitation is projected to increase in the entire Nepal during all time span (20’s, 50's and 80's) at A1, A1B, and B2 senarios ( Chapter 9, Table –9.1). Larger increase in precipitation is projected over Western Region with up to 60 mm and 80 mm increase per annum respectively during 20's and 50’s. Since high precipitation and flood/ landslide are directly related, any significant increase in precipitation as projected over these areas will increase the likelihood of flood and other related hazards.
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The effect of recent climate changes on river flows are not yet done extensively. The general perception is made on trends in three categories as large outlet rivers, southern rivers and snow‐fed rivers. Among the large rivers, Karnali and Sapta Koshi show a decreasing trend, Narayani (Kali Gandaki), shows an increasing trend. Southern rivers do not show any trend. All of the three snow‐fed rivers examined here show a declining trend in discharge. Preliminary trend analysis on observed records indicated that discharge trend is neither consistent nor significant in magnitude. It could be due to short record lengths and high inter‐annual variability in discharge data. Another study indicated that the number of flood days and consecutive days of flood events appeared to be increasing (Shrestha and Shrestha 2003).
A maximum monthly contribution of 22.52% is in May and a minimum monthly contribution of 1.86% is in January. 2.51% out of total 8.46% snow and glacier melt contribution is from Dudh Koshi sub‐basin (WWF 2009). This basin has maximum contribution to annual flow at Chatara. Arun and Tamor basins are two other major tributaries, Tamor, Arun and Dhudha Koshi share 84% Kosi flow at Chatara. Indrawati sub‐basin has minimum contribution to annual flow at Chatara (0.15% out of total 8.46%). (WWF 2009).
A nearly completed Namche Hydropower Project was washed away byDig Tsho Glacier Lake outburst flooded on 4 August 1985 in the Langmoche valley, Khumbu (Ives 1986; Yamada 1998). The lake, crescent in shape, was dammed by a 50 m high terminal moraine. The GLOF was caused by detachment of a large ice mass from the upper portion of the Langmoche glacier during clear weather condition in July. The ice mass overran the glacier and splashed into lake which was already full. Since then, Government of Nepal (GON) has considered GLOFs as a threat to the development of water resources of the country and has realized the necessity to carry out studies on glaciers and GLOFs. Intense precipitation events, increased floods, landslides, and sedimentation (particularly during the monsoon) are expected to result from climate change. Hydropower infrastructure and facilities are at risk. Hydroelectric plants are highly dependent on predictable runoff patterns,.
Ben Blackshear et al (2011) created an illustrated framework that shows relative changes in generation capacity due to climate change. Climate change effects are located along the x‐axis and the type and characteristics of hydropower schemes along the y‐axis (Chapter 4, Figure 4.2). Discharge, temporal variability, and glacial melt do not apply to pure pumped storage, which is not connected to a river network. Only evaporation is applicable to reservoir surface area to volume ratio (SA:Vol).]
The slight increase in temperature paired with an increase in precipitation suggests that the evaporation rates of the region will decrease slightly. This is added benefit to large surface reservoirs. The overall increase in precipitation will provide more water to the rivers, increasing the potential for hydropower generation. The increasing temperature in the Himalayas will increase the glacial melt that feeds the rivers, increasing discharge for at least the next several decades. However, once these glaciers have melted, there will be a decline in river’s discharge. South Asia’s climate and hydrological cycles are significantly impacted by the monsoon, which has already been altered by climate change (Science Daily, 2009). The monsoon delivers around 75 percent of the regions precipitation during roughly three months. The beginning of the monsoon is predicted to arrive later in the year, making the dry season longer and increasing the number of droughts (Science Daily, 2009). Similarly, there will be an increase
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in the severity of rainfall events as well as storms, causing overall increased temporal variability in water supply (McNally, A. 2009). The disparate distribution of precipitation timing in this area causes significant variations in river discharge (the Mekong River study). Various climate change impacts are interconnected and have significant repercussions for hydropower. As climate change impacts intensify, variation inflows will be exacerbated, making it more difficult for hydropower facilities to predict river discharge and to generate an even supply of power.
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Table of Content
Table of Contents
Acknowledgement ...................................................................................................................................... i
Research Team .......................................................................................................................................... ii
Executive Summary .................................................................................................................................. iii
List of Tables ............................................................................................................................................. x
List of Figures ........................................................................................................................................... xi
List of Abbreviations ............................................................................................................................... xiv
1. Study objectives and methodology ....................................................................................................... 1
2. HYDROPOWER ‐ Hydroelectricity .......................................................................................................... 3
2.1Typology of Hydropower Schemes............................................................................................... 4
2.2Pumped Storage .......................................................................................................................... 5
2.3Reservoir ..................................................................................................................................... 6
2.4 Run‐of‐river ................................................................................................................................ 6
3. CLIMATE change .................................................................................................................................... 7
3.1 Introduction ............................................................................................................................... 7
3.2 Past Climate changes .................................................................................................................. 8
3.3 Climate changes recent era ......................................................................................................... 9
Change in temperature .................................................................................................................. 11
Change in precipitation .................................................................................................................. 11
Change in specific humidity ............................................................................................................ 12
Change in annual runoff ................................................................................................................. 12
Glaciations ..................................................................................................................................... 13
4. CLIMATE Change effects pertinent to Hydropower Development ..................................................... 13
4.1 Evaporation .............................................................................................................................. 17
4.2 Discharge ................................................................................................................................. 17
4.3 Temporal variability of precipitation ........................................................................................ 17
4.4 Flooding ................................................................................................................................... 17
4.5 Droughts .................................................................................................................................. 18
4.6 Seasonal offset ......................................................................................................................... 18
4.7 Glacial melt .............................................................................................................................. 18
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5. Regional Findings ‐ Climate change impacts and implications for hydropower .................................. 18
5.1 North America .......................................................................................................................... 19
5.2South America ........................................................................................................................... 20
5.3 Europe ...................................................................................................................................... 21
5.4 Middle East .............................................................................................................................. 22
5.5 Africa .................................................................................................................................................. 23
5.6 Asian‐Pacific region .................................................................................................................. 24
5.7 Asia .......................................................................................................................................... 24
6. Major River Basins of Nepal ................................................................................................................. 27
6.1 First Grade Rivers ..................................................................................................................... 28
6.2 Second Grade Rivers ................................................................................................................. 29
6.3 Third Grade Rivers .................................................................................................................... 29
7. Hydropower Potential in Nepal ........................................................................................................... 29
8. Climate change in Nepal ...................................................................................................................... 32
8.1 Trend in Changes in average annual maximum temperature .................................................... 33
8.2 Trend in precipitation ............................................................................................................... 33
8.3 Climate change induced trend in Rainfall and Temperature ............................................................. 35
8.3.1 Rainfall ....................................................................................................................................... 35
8.3.2 Future Projection on Rainfall trend ........................................................................................... 37
9. CLIMATE Change impact in River flows pattern in Nepal .................................................................... 40
9.1 River Flows Pattern .................................................................................................................. 40
9.2 The effect of climate change in Nepalese river flows ................................................................ 46
10. Climate Change as it affects in Hydropower Production .................................................................. 47
10.1 Hydropower and Impact of Climate in Snow and Glacial areas ................................................ 48
10.2Consequence of Climate Change to Infrastructure ................................................................... 52
11. CONCLUSION, Adaptations and Policy Recommendation ................................................................. 53
Adaptation and policy recommendation ........................................................................................ 56
References ............................................................................................................................................... 58
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List of Tables Table 6.1: Geographic regions of Nepal
Table 7.1: Hydropower Potential of Nepal (identified 1 June, 2012)
Table 7.2: Existing power plants run by private companies.
Table 7.3: Load Forecast for Nepal
Table 8.1 : Regional mean maximum temperature trends for the period 1977–1994 (degree C/year)
Table 8.2: GCM Estimates for temperature and precipitation changes in Nepal
Table 8.3: Projected change for temperature and precipitation under different scenario averaged over Central Himalayan region
Table 10.1:. Priority ranking of climate change impacts for Nepal
Table 10.2: Annual snow and glacier melt contribution (in %) for increased temperature scenarios
Table 10.3: Contribution (%) of glacierized sub‐watersheds of each sub basins to the total flow at downstream stations
Table 10.4: List of GLOF events recorded in Nepal
Table 11.1: Temperature Sensitive Glaciated Areas of the Major River Basins inNepal.
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List of Figures Figure 1.1: The Global Water System Project’s Global Reservoirs and Dams Database (GRanD).
Figure 1.2: Existing Power plants in Nepal
Figure 2.3 : Project site photo of Karnali Chisapani Multipurpose Project
Figure 2.1: Hydrological Cycle
Figure 2.2: Example of Hydroelectric System
Figure 2.3: Types and characteristics of hydropower schemes.
Figure 2.4: Pumped storage hydropower.
Figure 2.5: Reservoir hydropower.
Figure 3.1 Greenhouse gas effect
Figure 3.2: Reconstructions of (Northern Hemisphere average or global average) surface temperature variations from six research teams
Figure 3.3 : Carbondioxide Concentration projection ( Ice core analysis)
Figure 3.5 Temperature Variations (Tree ring rings analysis.)
Figure 3.5: Predicted global change in mean annual air temperature, 2011‐2030
Figure 3.6: Predicted global change in mean annual precipitation, 2011‐2030.
Figure 3.7: Predicted global change in specific humidity, 2011‐2030.
Figure 3.9: Glaciated watersheds of the world.
Figure 4.1: Flow chart of climate change effects
Figure 4.2: Framework of climate change effects on different characteristics of hydropower schemes. Figure 5.1: Predicted monthly discharge changes for four dams on the Peribonka River in Quebec, Canada
Figure 5.2: Predicted changes in river discharge across Europe by two models, for 2020s and 2070s. Figure 5.3: Asian hydropower dependence. Percent of total installed capacity dedicated to hydropower.
Figure 6.1: River system and North‐South Topographical difference
Figure 7.1: Load Forecast
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Figure. 8.1: Projections of changes in monsoon precipitation (top) and average annual temperature (bottom) by the end of the twenty‐first century for emission scenario SRES‐A2 (left) and B2 (right)
Figure 8.1: Annual rainfall (mm/year) trend
Figure 8.2: Pre‐monsoon rainfall (mm/year) trend
Figure 8.3: Monsoon rainfall (mm/year) trend
Figure 8.4: Post‐monsoon rainfall (mm/year) trend
Figure 8.5: Winter rainfall (mm/year) trend
Figure 8.6: 24 hour’s highest rainfall (mm)
Figure 8.7: Mean annual Change in precipitation (in millimeter) for B1 scenario (a) 2020's (b)2050's (c) 2080's
Figure 8.8: Mean annual Change in precipitation (in millimeter) for A1B scenario (a)2020's (b) 2050's (c) 2080's
Figure 8.9: Mean annual Change in precipitation (in millimeter) for A2 scenario (a) 2020's (b) 2050's (c) 2080's
Figure 9.1: Location of three major rivers system, Kosi, Narayani and Karnali
Figure 9.2 : Trend in mean annual discharge of Kosi
Figure 9.3: Annual flows deviation in Kosi
Figure 9.4 Trend in mean annual discharge of Tamur
Figure 9.5: Annual flows deviation in Tamur
Figure 9.6: Trend in mean annual discharge of Narayani
Figure 9.7: Annual flows deviation in Narayani
Figure 9.8: Trend in mean annual discharge of Chepe
Figure 9.9: Annual flows deviation in Chepe
Figure 9.10: Trend in mean annual discharge of Karnali
Figure 9.11: Annual flows deviation in Karnali
Figure 9.12: Trend in mean annual discharge of Chamelia
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Figure 9.13: Annual flows deviation in Chamelia
Figure 9.14: Trend in mean annual discharge of Kankai
Figure 9.15: Annual flows deviation in Kankai
Figure 9.16: Trend in mean annual discharge of Bagmati
Figure 9.17: Annual flows deviation in Bagmati
Figure 9.18: Trend in mean annual discharge of Lothar and Manahari river
Figure 9.19: Percent difference in mean annual flows with longterm of Loth
Figure 9.20: Trend in mean annual discharge of W Rapti
Figure 9.21: Annual flows deviation in W Rapti
Figure 9.22: Trend in mean annual discharge of Bagmati
Figure 9.23: Annual flows deviation in Bagmati
Figure 9.24: Annual runoff and rainfall volume
Figure 9.25: Flow recession curves
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List of Abbreviations AOGCM Atmosphere Ocean Coupled General Circulation Models
AR4 Fourth Assessment Report
CBS Central Bureau of Statistics
CCCM Canadian Climate Change Model
CDM Clean Development Mechanism
CDR Central Development Region
CH4 Methane
CO Carbon Monoxide
CO2 Carbon Dioxide
DDC District Development Committee
DFRS Department of Forest Research Survey
DHM Department of Hydrology and Meteorology
EDR Eastern Development Region
EIA Environmental Impact Assessment
EPA Environment Protection Act
EPC Environment Protection Council
FWDR Far‐Western Development Region
GCM Global Circulation Model
GCM General Circulation Models
GHG Greenhouse Gases
GHG Greenhouse Gas
GIS Geographical Information System
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GIS Geographical Information System
GLOF Glacier Lake Outburst Flood
ICIMOD International Center for Integrated Mountain Development
IPCC Intergovernmental Panel on Climate Change
IPCC Inter governmental Panel on Climate Change
IUCN International Union for Conservation of Nature
m.a.s.l. meter above sea level
m3/s cubic meter per second
MoEST Ministry of Environment, Science and Technology
OECD Organization for Economic Co-operation and Development
SOHAM-Nepal Society of Hydrologists and Meteorologist-Nepal
SRES Special Report on Emission Scenario
UNFCCC United Nations Framework Convention on Climate Change
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1. Study objectives and methodology The role of hydropower in national energy and regional cooperation is expanding at all part of the globe. Figure 1.1 presents global database of dams and reservoirs by the Global Water System Project’s Global Reservoirs and Dams Database (GRanD)( Lehner et al 2011) updated in March 2011. The percentage of a country’s energy portfolio that is made up of hydropower is different from country to country. Variations in hydroelectric production on communities and economies have significant impacts on human livelihoods. Nepal posses an appreciable of hydroelectricity which is more than 83 thousand MW (Shrestha, Hariman). Nepal is able to exploit only less than two percent (Figure 1.2) of its potential. Country’s hydroelectric dependency refers to the percent of total installed capacity dedicated to hydropower. Photo 1 is a location of a project site of 10800 MW capacity hydropower project found feasible in Karnali river of Nepal.
Figure 1.1: The Global Water System Project’s Global Reservoirs and Dams Database (GRanD). Data: Global Water Systems Project, 2011.
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Figure 1.2: Existing Power plants in Nepal
Figure 2.3 : Project site photo of Karnali Chisapani Multipurpose Project.[ A 270 meter high rock fill main dam with an installed capacity of 10,800 MW and 24 meter high re‐regulating dam (at 8 km downstream
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of the main dam) with an installed capacity of 84 MW (6x 14 MW) is seen feasible. The Irrigation potential in Nepal is 191,000 net hectors and 3,200,000 gross hectors in India.]
The current global trends in climate have been affecting every corner of the globe at all aspects. The effects on precipitation pattern and hydrological regime also are most critical to hydropower generation. The scope of this report limits to the impacts that alters electricity availability from hydropower due to climate change in Nepal.
This study views also on how climate change has been adding challenge and open new opportunity to hydropower developments in Nepal. This study is also intends to assist hydropower developer and decision‐makers in integrating the present state of hydrology, and the vulnerability of hydroelectric generation to climate change. This study is expected to be helpful in indentifying indicators in the Nepalese context that would best represent the type of vulnerability to be pursued
The methodology of this study is based on research output made available as published literatures. Various scientific studies’ results and information from multiple sources that are focused on climate change vulnerability to water resource, especial focus on hydropower are synthesized and integrated. Important parameters of a hydroelectric generation are installed capacity, output wattage, and stream flows. Climate change impacts range from changing precipitation patterns, increasing glacial melting, alteration on stream flows and increased occurrence of extreme weather events. This study basically refers vulnerability to a hydropower generating facility’s potential to have its electrical generation altered by climate change. This report focuses on impacts related to changes in temperature and precipitation. Some of case studies along with dam characteristics in view of climate change impacts, and projected climate change impacts are presented.
2. HYDROPOWER ‐ Hydroelectricity The solar energy which drives the Hydrologic Cycle is utilized efficiently in hydropower (Figure 2.1). Potential energy possess by water due to height difference between forbay (intake) to orifice of pen stroke pipe is used to rotate generator through turbine for electricity production (Figure 2.2). Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy, accounting for 16 percent of global electricity consumption, and 3,427 terawatt‐hours of electricity production in 2010, which continues the rapid rate of increase experienced between 2003 and 2009.
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Figure 2.1: Hydrological Cycle Figure 2.2: Example of Hydroelectric System
Power of water has been used since ancient times to grind flour and perform other tasks. In the mid‐1770s, French engineer Bernard Forest de Bélidor published an article titled as Architecture Hydraulique which described vertical‐ and horizontal‐axis hydraulic machines. By the late 19th century, the electrical generator was developed which is now coupled with hydraulics. In 1878 the world's first hydroelectric power scheme was developed at Cragside in Northumberland of England by William George Armstrong. Hydroelectric power plants continued to expand widely throughout the 20th century. Hydropower was referred to as white coal for hydroelectricity. Hoover Dam's initial 1,345 MW power plant built in 1936 was the world's largest hydroelectric power plant till 1941. It was eclipsed by the 6809 MW Grand Coulee Dam in 1942. The Itaipu Dam opened in 1984 in South America as the largest, producing 14,000 MW but is surpassed by the Three Gorges Dam in China at 22,500 MW in 2008. Hydroelectricity would eventually supply some countries, including Norway, Democratic Republic of the Congo, Paraguay and Brazil, with over 85% of their electricity. The United States currently has over 2,000 hydroelectric power plants which supply 49% of its renewable electricity.
An argument which is not exclusive in hydropower is whether or not large hydro systems bring benefits to the poorest has also been questioned (Collier, 2006). The multiple benefits of hydro‐electricity, including irrigation and water‐supply resource creation, rapid response to grid‐demand fluctuations due to peaks or intermittent renewable. Recreational lakes and flood control, need to be taken into account for any given development. Several sustainability guidelines and an assessment protocol have been produced by the industry (IHA, 2006; Hydro Tasmania, 2005; WCD, 2000).
2.1Typology of Hydropower Schemes A structural characteristic of hydropower schemes is related with types (Figure 2.3) like pumped storage, reservoir, and run‐of‐river (Egre, D., & Milewski, J. C, 2002). In general, pumped storage and reservoir hydropower are evaluated in terms of the storage capacity and surface area(SA) to volume (Vol) ratio (SA:Vol) of their reservoirs. Electrical demand varies from peak hours to non‐peak hours. The
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time of day and season of the highest electrical demand refer to peak hours whereas non‐peak refers to times of relatively low electrical demand.
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Figure 2.3: Types and characteristics of hydropower schemes. Reservoir surface area to volume ratio (SA:Vol) and reservoir size are only applicable to reservoir and pumped storage schemes. For the purpose of this report, the categories of ‘high,’ ‘low,’ ‘large,’ and ‘small’ are relative, not definite terms. (Source: Egre, D., an Milewski, J. C; 2002).
2.2Pumped Storage Pumped storage hydropower stores water as potential energy for electricity production. This power for storing water comes often comes from other sources or from unused such as wind and nuclear electricity (IPCC, 2011) or from off hour electricity from other projects. Typically, electricity from these other sources is used to pump water up to a higher reservoir (Figure 2.4) during off‐peak hours. During peak hours, the water is released to the lower reservoir to generate electricity. Pumped storage, in which the reservoirs are not Pumped storage is most commonly found in North America, Europe, and Asia (Egre & Milewski. 2002).
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Figure 2.4: Pumped storage hydropower. (Source: Edenhofer et al. 2011).
2.3Reservoir Most commonly, hydropower dams partially block the water flow of a river and store water upstream of the dam to create a reservoir (Figure 2.5). Stored water in the reservoir is used to produce electricity at desired time and is better able to withstand fluctuations in river flow. Larger reservoirs can buffer greater fluctuations in flow over a longer time period to provide both base and peak power generation, while smaller reservoirs typically provide only base power generation because of the impacts of variable discharge rates. Reservoir dams are found worldwide (Egre & Milewski, 2002).
Figure 2.5: Reservoir hydropower. ( Source Edenhofer et al. 2011)
2.4 Run‐of‐river Run‐of‐river facilities have no storage capacity to buffer fluctuations in water flow. Run‐of‐river dams utilize some or all of a river’s flow to produce electricity without impounding any significant amount of water upstream (Figure 2.6). These facilities provide only base power generation, lacking the ability to
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store water for periods of peak demand. However, an upstream reservoir dam may act as storage for downstream run‐of‐river dams, restricting the flow during off‐peak periods and releasing more water during periods of peak electricity demand Run‐of‐river hydropower is found most commonly in North America, Europe, and Asia
Figure 2.6: Run‐of‐river hydropower. From Edenhofer et al. 2011.
3. Climate Change
3.1 Introduction On the broadest scale, the rate at which energy is received from the sun and the rate at which it is lost to space determine the equilibrium temperature and climate of Earth (Figure 3.1). This energy is then distributed around the globe by winds, ocean currents, and other mechanisms to affect the climates of different regions in the earth.
Figure 3.1 Greenhouse gas effect
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IPCC defined "climate change" as: "a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods". Climate change refers to any significant change in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer).
UNFCCC: United Nation framework Conventions on Climate Change in its Article 1 defines climate change as a change of climate, which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time period. (Decades or longer).
The inherent characteristic of climate is that it changes with time ‐"climate variability“.
The degree of climate variability that is described by the differences between long‐term statistics of meteorological elements calculated for different periods is the measure of climate change.
3.2 Past Climate changes The most recent period in the geological record is called Holocene age. It began at the time of retreat of the continental ice sheets at the end of the last glaciations, which occurred at about 10 000 calendar years before present. The climate during the Holocene period appeared relatively stable but there were significant climate fluctuations during this period (e.g. Bond et al. 1997; Mayewski et al. 1997; deMenocal et al. 2000). The tropical region indicates a rapid warming from the early to mid Holocene followed by a relatively weak. Warming during the late Holocene. The dominant modes of Holocene variability seemed around 2300 and 1000 years. Temperature reconstructions derived from terrestrial vegetation (Huntley and Prentice 1988) and mountain glaciers (Porter and Orombelli 1985) is also understood as the Holocene Climatic Optimum This warm period is also observed (Crowley and North1991). The graph (Figure 3.2) provides reconstructions of Northern Hemisphere average or global average surface temperature variations over the last 1,100 years from six research teams, along with the instrumental record of global average surface temperature. Overall, the curves show a warming around 1000 AD followed by a long general cooling trend that continues until the early 1900s. Each curve illustrates a somewhat different history of temperature changes, with a range of uncertainties that tend to increase backward in time.
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Figure 3.2: Reconstructions of (Northern Hemisphere average or global average) surface temperature variations from six research teams (in different colour shades) along with the instrumental record of global average surface temperature (in black). [Reconstructions© (2006) by the National Academy of Sciences]
3.3 Climate changes recent era Current debate on climate changes is blamed to green house gases. Scientists have been examining various causes for this warming trend: looking at the impact on temperature of natural variations, volcanic activity, changes in solar activity, urban heat effects and more. However the significant cause of the warming trend is seen as the ‘Greenhouse Effect’ – a well‐understood phenomenon that was discovered in 1824 and first measured in 1859 (IPCC Assessment Report 4, 2007).
The major greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N20). Some concentrations of GHGs in the atmosphere are natural but human activity is producing more and more of these gases each year, The human influence contributed more carbon dioxide than any other greenhouse gas. Currently the CO2 concentration in the atmosphere is more than 390 parts per million (ppm) (Data from Mauna Loa observatory – monthly average as viewed April 2010), significantly higher than the pre‐industrial figure of around 280 ppm. (IPCC AR4 WG1) (Figure 3.3 and 3.4)
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Observation tells us the world is warming. Global average temperatures, calculated from networks of weather stations around the world, show a persistent warming trend (IPCC Assessment Report 4, 2007). The Earth’s average temperature has increased by 0.75°C over the past 100 years. (UK Met Office HadCRUT3
temperature record)
Eleven of the 12 years from 1995 to 2006 are among the 12 warmest years on record (IPCC AR4 WGI).
Indeed, the 10 warmest years from the UK Meteorological Office’s 160‐year records are all since 1997, while eight of them are after 2001. (UK Met Office HadCRUT3 temperature record) Global average temperature trends are calculated by the UK Meteorological Office, which works with the Climatic Research Unit (CRU) at the University of East Anglia, and in the United States by the Goddard Institute for Space Studies (GISS) at NASA and by the National Oceanic and Atmospheric Administration (NOAA). Each of these three groups uses different methods to collect and process data – but they come out with very similar results and the same long‐term warming trend. This trend in surface temperatures has been reflected in similar warming trends in atmospheric and ocean temperatures. Furthermore the impact of increased temperatures can be observed in changes in the environment such as sea‐level rise and widespread loss of glaciers and snow cover (IPCC AR4 WGI). Some scientists have speculated that Arctic would completely ice‐free during summers in the in the next few towards the end of the twenty‐first century (PIRC, 2008, IPCC AR4 WG1). The warming of the past 50 years was unprecedented in the last 1,300 years at least and probably for several millennia. It is assumed that the last time the poles were significantly warmer for a long period, sea levels were 4‐6m higher than they are now (IBID)
Figure 3.3 : Carbondioxide Concentration projection ( Ice core analysis) Source : Time for Climate Justice, June 2010
Figure 3.5 Temperature Variations (Tree ring rings analysis.) Source : Time for Climate Justice, June 2010
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Prediction is made by scientists (IPCC, 2007). Predicted global change in mean annual air temperature (Figure 3.5), precipitation (Figure 3.6), specific humidity (Figure 3.7), annual runoff (Figure 3.8), and glaciations (Figure 3.9), are given in figures below.
Change in temperature
Figure 3.5: Predicted global change in mean annual air temperature, 2011‐2030. Air temperature anomaly in degrees Kelvin. Data: IPCC DDC, NCAR CCSM3 based on SRA2 scenario.
Change in precipitation
Figure 3.6: Predicted global change in mean annual precipitation, 2011‐2030. Precipitation flux anomaly (kg∙m‐2∙s‐1). Data: IPCC DDC, NCAR CCSM3 based on SRA2 scenario.
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Change in specific humidity
Figure 3.7: Predicted global change in specific humidity, 2011‐2030. Specific Humidity Anomaly (ratio). Data: IPCC DDC, CCSR/NIES/FRCGC MIROC3.2 based on SRA2 scenario.
Change in annual runoff
Figure 3.8: Predicted global change in annual runoff, 2090‐2099.
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Water availability in percent, relative to 1980‐1999. These predictions may not necessarily reflect changes over a shorter timescale. Map adapted from IPCC DDC.
Glaciations
Figure 3.9: Glaciated watersheds of the world. This map uses components of the USGS HYDRO1k Pfafstetter watershed delineation system to represent the drainages of the world that contain glaciers. Dams located within those glaciated drainages are also shown. Data: GRanD Dam Database 2011, USGS HYDRO1k 2011.
4. Climate Change effects pertinent to Hydropower Development The flow chart below (Figure 4.1) was designed to identify the types of climate change effects predicted in different parts of the world (Blackshear, 2011). The flow chart is designed to show the complex ways in which the two most important climate change effects, changes in precipitation and temperature, will impact hydropower (Izrael, Y. ,2007, IPCC 2007). The maps show specific predicted climate change effects: global changes in precipitation, temperature, specific humidity, and runoff, as well as current glaciated watersheds of the world. The final boxes on the flow chart are the changes in river discharge, which is what broadly determines how much electricity a given hydropower facility can generate.
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Figure 4.1: Flow chart of climate change effects. Red indicates effects that are typically detrimental to hydroelectric production, and blue indicates effects that typically improve hydroelectric production potential.
To understand how climate change will affect hydropower production, it is necessary to consider the ways in which characteristics of hydropower facilities affect their vulnerability to climate change. To explain these interactions, Ben Blackshear et al (2011) created an illustrated framework that shows relative changes in generation capacity due to climate change. Climate change effects are located along the x‐axis and the type and characteristics of hydropower schemes along the y‐axis (Figure 4.2).
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Figure 4.2: Framework of climate change effects on different characteristics of hydropower schemes. [Climate change impacts are shown along the x‐axis, and hydropower characteristics, are shown down the y‐axis. Discharge, temporal variability, and glacial melt do not apply to pure pumped storage, which is not connected to a river network. Only evaporation is applicable to reservoir surface area to volume ratio (SA:Vol).]
Not only Nepal, south Asian region will face unique challenges as climate continues changing. Glacial melt due to increasing temperatures variability in the timing, location and amount of precipitation and, Floods, droughts, and are all symptoms of climate change that will affect hydroelectric generation. Developing countries like Nepal are inherently more vulnerable to the effects of climate change disruptions because they have fewer disposable resources to spend on unexpected extreme weather events and on adapting to long‐term alterations.
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Changes in temperature and changes in precipitation patterns have profound effects on river systems. These impacts directly affect hydroelectric production. Rapidly melting glaciers in the Rocky Mountains, the Andes, and the Himalaya change the already variable hydrographs of the rivers they feed. Severe storms caused by warming ocean temperatures have the capacity to threaten hydropower infrastructure and flood entire regions. Hydropower is dependent on river discharge to create electricity. Generally, the lower the river discharge, the less electricity a hydropower facility can generate. Differing scales and types of hydropower are more vulnerable to climate change phenomena. Our study considers how projected climate change impacts will affect hydropower vulnerability across the globe.
Though hydropower is widely considered to be a renewable resource and a low emissions alternative to fossil fuels, it comes with its own set of environmental impacts. Many of these impacts will likely intensify as the effects of climate change become more severe. Hydropower already constitutes a significant proportion of many countries’ energy portfolios. Some countries, such as China, have already made massive investments in hydropower in their own country as well as abroad. Certain regions are dominated by large‐scale hydropower while others are powered through smaller scale hydropower projects. Due to the global scope of this study, we focus on larger projects. Future plans for hydroelectric generation vary greatly from region to region, as do the effects of climate change. Across North America, concerned environmentalists are working to decommission large dams, while areas in Asia, Latin America, Africa, and the Middle East are in the process of building large dams
An review of World Energy till 2004 made by British Petroleum shows that large hydroelectricity systems (>10 MW) contribute over 2800 TWh of consumer energy (BP, 2006) that also accounts to about 16% of global electricity and 90% of renewable electricity IPCC (2007). Expansion of Hydro projects is gearing up particularly in China, India, Brazil and potential rich country like Nepal. The global technically potential of small and micro hydro is around 150–200 GW which is only a part of large potential left yet to be exploited. Evaluations of hybrid hydro/wind systems, hydro/hydrogen systems and low‐head run‐of‐river systems are under review (IEA, 2006d). About 75% of water reservoirs in the world were built for irrigation, flood control and urban water‐supply schemes can have small hydropower generation schemes. Small (<10 MW) and micro (<1 MW) hydropower systems, usually run‐of‐river schemes, have provided electricity to many rural communities in developing countries such as Nepal. Hydro plants capacities are determined as per prevailing requirements. The 12.6 GW Itaipu plant in Brazil/Paraguay, are run as base load generators with an average capacity factor of >80%, whereas the 24 GW of pumped storage plant in Japan is used mainly as fast‐response peaking plants, giving a factor closer to 40% capacity.
But social disruptions, ecological impacts on existing river ecosystems including fisheries are stimulating public opposition due to water diversion and evaporative water losses. The GHG footprint of hydropower reservoirs has been in questioned (Fearnside, 2004; UNESCO, 2006). Some reservoirs have been shown to absorb CO2 at their surface, but most emit small amounts as water conveys carbon in the natural carbon cycle (Tremblay, 2005). High emissions of CH4 have been recorded at shallow plateau‐
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type tropical reservoirs where the natural carbon cycle is most productive (Delmas, 2005). Deep water reservoirs at similar low latitudes tend to exhibit lower emissions. Methane from natural floodplains and wetlands may be suppressed if they are inundated by a new reservoir since the methane is oxidized as it rises through the covering water column (Huttunen, 2005; dos Santos, 2005). Methane formation in freshwater produces by‐product carbon compounds (phenolic and humic acids) that effectively sequester the carbon involved (Sikar, 2005).
Evaporation, discharge, temporal variability, and glacial melt impact the vulnerability of certain hydropower facilities and reservoir characteristics as mentioned below.
4.1 Evaporation Increased evaporation will reduce electricity generation for all types of dams, but these effects will be most drastic for those with reservoirs. Due to the direct relationship between the surface area of a body of water and its rate of evaporation, the geometry of reservoirs determines how susceptible they are to evaporation (McJannet et al, 2008) Reservoirs with higher surface area to volume ratios are more vulnerable to losing capacity from evaporation, which reduces a facility’s power production capacity (Izrael, Y.(2007). Retrofitting reservoirs to make them deeper with a smaller surface area would reduce evaporation; however it is very expensive (McJannet et al, 2008). Planned projects should take reservoir shape into consideration in their design in order to reduce evaporation and maximize power potential. Reservoir size is important to evaporation as well, as smaller reservoirs will be more at risk to losing greater proportions of their volume, as reflected in the above illustrated framework.
4.2 Discharge Though an increase in amount of annual river discharge can sometimes simply translate to an increase in hydropower production, fluctuations in discharge affect different types of facilities differently. Run‐of‐river dams, for example, may be more vulnerable to decreased amounts of discharge because they are directly dependent on the river’s flow, whereas reservoir dams may be able to compensate better for decreased amounts of water by adapting the management plan for the reservoir volume. In our diagram, discharge refers to the annual discharge, which can be directly correlated to changes in precipitation. It does not address other issues such as temporal variability, which we account for in another section.
4.3 Temporal variability of precipitation Climate change will cause increased temporal variability of precipitation events. This will pose significant problems for hydroelectric generation. These impacts will result in more severe and frequent floods and droughts. Seasonal offsets, or the altering timing and magnitude of precipitation for traditional rainy and dry seasons and peak snowmelt, will occur as well (Izrael, Y. 2007).
4.4 Flooding By delivering water supply at varied and unpredictable times, temporal variability negatively impacts hydroelectric production. However, it impacts reservoir dams less than run‐of‐river facilities because reservoir dams have the capacity to store water, thereby accounting for these variations in reservoir volume. Dams can control the flood pulse of a river and help buffer downstream areas from dangerous
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impacts (Hauenstein, W., 2005). Flooding has the potential to increase river flows and hydropower generation as long as the excess river flow level remains within the dam’s reservoir capacity.
4.5 Droughts Droughts may present the most obvious threat to hydroelectric generation, as they reduce the amount of water available to produce electricity. Many regions have experienced droughts in the last several decades that greatly reduced energy production, reducing up to half of their electrical production capacity in some Cases (Sailor D.J., Muñoz J.R., 1997). A 2009 study in the western United States, which modelled the impact of drought scenarios on electricity generation, found that hydroelectric generation would be reduced by 30 percent (National Energy Technology Laboratory (2009). Droughts in areas exclusively dependent hydropower for electricity generation would face blackouts in some drought scenarios.
4.6 Seasonal offset The seasonality of precipitation causes variability in hydroelectric generation. Regions with distinct seasonal rain cycles and snowmelt seasons typically experience fluctuations in generation due to precipitation’s influence on flow. Munoz and Sailor note that “Under global warming, the existent difference between the generation in fall‐winter and spring‐summer will increase.” Sailor and Muñoz. (1997). Thus power production will indeed increase relative to current rates during part of the year; however, this will be counteracted by sharp decreases in other months. The magnitude of climate change induced precipitation shifts will vary greatly by season. In some cases precipitation is projected to be reduced twice as much in one season while in other regions, wet seasons may become drier and the dry seasons may become wetter (Harrison, G. P., & Whittington, H. (2002)
4.7 Glacial melt Glaciated regions of the world act as natural water towers that provide water to downstream areas. As glaciers continue to retreat in response to climate change, runoff to rivers will initially increase in the short‐term due to the large volumes of stored ice melting away. Eventually these stores of ice may disappear entirely, however, resulting in a long‐term decrease in annual runoff and stream discharge. (Huss, M. (2011).
5. Regional Findings ‐ Climate change impacts and implications for hydropower Neither river systems nor climate change affects are constrained by manmade political boundaries. Many case studies and data sets are regional. Regional findings provided a preliminary basis for collecting information that climate change impacts will most significantly impact hydropower generation across the globe. A type of dam characteristics determines affects on them by types of climate change impacts. The severity and type of these impacts vary significantly each regionally. The other factors determining the responses to climate change impacts on hydropower generation are political, social and economic factors, unique to the region. Regional portfolios of North America, South America, Europe, and the Middle East, Africa, and Asia‐Pacific and. Asia is copied below for references.
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5.1 North America The United States and Canada rank among the top four largest hydroelectricity producers in the world. Mexico is considerably less developed with regards to hydropower in the region. But the country has some very large dams currently operational and some potential sites for additional large and small‐scale dams are proposed to be constructed (U.S. Energy Information Administration. (2011).
The expected long‐term increase of annual and seasonal precipitation in parts of Canada has the capacity to increase hydroelectric output in those areas. One study in the Peribonka River watershed in Quebec, Canada predicted mean annual hydropower to decrease by 1.8 percent between 2010‐2039 due to initial early peak flows and lack of summer precipitation) and subsequently increase by 9.3 percent and 18.3 percent during 2040‐2069 and 2070‐2099 respectively due to steadily increasing precipitation amounts (Minville et al, 2009). This initial decrease in production is expected to hit run‐of‐river dams harder than reservoir dams, as they are unable to absorb the impact of low summer flows through storage of river water from earlier in the year. There are a couple of predicted negative impacts: firstly, the increased volatility of discharge due to more frequent extreme events. Changing seasonal patterns is expected to lower the reliability of reservoirs to store water efficiently, resulting in more unproductive overspill; and secondly, peak flows are expected to come earlier with less discharge, as can be seen in Figure 5.1, which analyzes four of the dams in the Peribonka River basin (Minville et al, 2009)
Figure 5.1: Predicted monthly discharge changes for four dams on the Peribonka River in
Quebec, Canada. (Minville et al., 2009).
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The prediction in increasing temperature and decreasing in rainfall on the Pacific Northwest of the United States have likely a negative effect on mean annual discharge, and in hydroelectric production. Some predictions forecast a 40 percent loss in production by 2080. Earlier snowmelts will shift seasonal peak flow time thereby hurting hydroelectric production, especially during the summer when it’s needed most (Power Markets Week, 2005) in the dry north and northwestern parts of Mexico. If temperatures increase significantly, though, droughts could threaten hydroelectric plant production in all parts of the country (Boyd, R., & Ibarrarán, M. E. 2009).
5.2South America Of all of the regions in the world, Latin America is one of the most reliant on hydropower for its energy production. Installed hydropower capacity in Latin America has the potential to produce approximately 140,000MW, or between 50‐60 percent of the region’s energy demands (U.S. Energy Information Administration, 2011). All nations in Latin America rely significantly on hydropower as an important energy resource. Brazil, Paraguay, Venezuela, and Costa Rica are most reliant on hydropower, which provides over 80 percent of their electricity supply.
Brazil has the largest reserve of surface freshwater on the planet nearly 20 percent of the global supply and most of that found in the relatively undeveloped regions of the Amazon River (Castano, 2011). Argentina and Chile share the world’s third largest store of ice as well as all of the rivers that compose the region of Patagonia. The northwestern sector of South America including Peru, Bolivia, Ecuador, and Colombia has started to discover their hydropower potential.
Climate changes in Latin America show a great deal of variability across the region. Different projections associated with evaporation and precipitation makes difficult to make stream flow projections. Projections related to climate change vary significantly at regional levels from model to model. (Izrael, Y. 2007). The variation in model output is believed due to the smaller hydrometereological observation network in Southern Hemisphere (Soito, J. L., Freitas D. S. 2011). However, it can be expected that general changes in rainfall patterns will occur and, increased frequency of extreme rainfall events throughout the region will lead to greater instances of flooding over larger areas and longer periods of time. Greater rainfall is expected in the River Plate Basin between Argentina and Uruguay due to the trend of increasing rainfall in the region from 1960 to 2000. There have been notable decreases in rainfall over western Chile and Peru, leading to the prediction that rainfall levels will continue to decrease on the Pacific side of South America in the near future. The Amazon River watershed is predicted to feel significant effects of climate change over the next half century. The region is expected to receive markedly less rainfall with increased intensity of the El Niño Southern Oscillation. The zone of Latin America i.e. the Amazon plains of Bolivia, Peru, and western Brazilhas have great impacts on the downstream variability in the Amazon River discharges. Changes in river flows in Latin America are mainly associated with changes in rainfall as well as changing land use practices. Due to the relatively drier climates in the Amazon associated with the El Niño Southern Oscillation, significant decreases in stream outflow in parts of the Amazon and Tocantins river basins are expected. The Paraná River which contains more than 55 percent of Brazil’s installed hydroelectric capacity as well as great hydroelectric generation potential for Argentina, Paraguay, and Uruguay is projected to experience river flows that
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are significantly higher than today due to increased rainfall amounts throughout the River Plate drainage basin. Thus Hyrdro industries will require developing more flexible approaches to managing reservoirs (Soito and Freitas, 2011).
5.3 Europe The topography of Europe has favoured wide variety of hydropower types including pumped storage, run‐of‐river, and reservoirs. The Alps, which stretch across France, Switzerland, Italy, Germany, and Austria, provide much of the changes in topography that provide hydropower potential to Western Europe. There is a high concentration of reservoir dams in mountainous and glaciated areas, including the Alps, the Pyrenees, and Norway. Hydropower accounts for approximately 19 percent of Europe’s total installed electric capacity (U.S. Energy Information Administration, 2011). Model predictions vary with availability of water. It is likely to increase across northern Europe and decrease in southern and south‐eastern Europe (Figure 5.2). Over the next several decades (Lehner et al; 2005). Specific changes in flow regime and characteristics of existing hydropower systems will guide on hydropower production in the countries and regions within Europe.
Figure 5.2: Predicted changes in river discharge across Europe by two models, for 2020s and 2070s. (Source: Lehner et al. 2005)
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In south and south‐eastern Europe, likelihood of droughts is increased and decrease in precipitation that will lead to reduced water availability in 2070. So there will decline in hydropower production correspondingly about 20 to 50 percent in counties like, Portugal, Spain, Ukraine, and Bulgaria (Lehner et al. 2005). In the short‐term, glacially fed rivers, such as those originating in the Alps and Pyrenees, will likely see increases in summer discharge as glaciers melt faster than they regenerate. Already, rivers in the Alps are seeing 13 percent increases in flow in August compared to two decades ago, and many glaciers have diminished significantly (Huss, M, 2011). In the long‐term, the contribution of these retreating glaciers to river flow will decrease, by 15 to 45 percent by the end of this century (Lehner et al. 2005).
Scandinavia and northern Russia will have increased water availability. But this change does not necessarily translate to a direct, equivalent increase in hydropower production. Run‐of‐river dams in Sweden are particularly susceptible to changes in flow pattern because of their inability to store discharge that exceeds maximum production capacity. Thus, an analysis of the impacts of climate change on hydropower in northern Europe must examine not only production capacity and changing water availability, but also the type of hydropower facilities. Overall across Europe, developed hydropower potential is predicted to decrease 7 to 12 percent by the year 2070 (Lehner et al, 2005). These decreases must also be considered within a broader context of increased water and electricity usage.
5.4 Middle East The Middle East lies in a transition zone between the temperate, wet climate of Central Europe and the arid climate of North Africa. With the desert environments of the Arabian Peninsula to the south, and the wet mountainous regions of Turkey and Iran to the north and east, even small shifts in climatic patterns are likely to have tremendous impacts on the region’s climate. (Giorgi, F. 2008).
The Middle East’s surface hydrology is primarily defined by the Tigris‐Euphrates River Basin, which boasts a mean annual stream flow of 85 billion cubic meters (BCM).( Cullen, 2002) Originating in Turkey, the Tigris River flows contains about 86 percent of flow that is derived from surface runoff and snowmelt within Turkey. (Cullen, 2002) The Zargos Mountain Range maintains a climate of considerable precipitation, which provides various river basins with snowmelt and surface runoff which facilitate powerful stream flow.
The Middle East’s climatic variations are in large part due to the North Atlantic Oscillation Pattern (NAO). The NAO regulates heat and moisture fluxes in the Mediterranean Region and ultimately influences climate patterns throughout the Middle East. (Turkes, M., 1996). Over the past 150 years, this climatic pattern has provided the Mediterranean and Middle East with much of, its precipitation in the form of wet winters (Hurrell, J.W., 1995). The NAO transports winter cyclones to the area, and large amounts of precipitation with them. Cullen et al (2002) noted that increased greenhouse gas (GHG) concentrations in the atmosphere would significantly impact the regional precipitation patterns. Specifically, “December through March precipitation and stream flow can be expected to be lower” (Cullen et al. 2011) due to climate change. As the NAO is a significant contributor to snow accumulation,
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the ultimate sources of both the Tigris and Euphrates Rivers, climate change will have a major impact on region’s flow rates (Sowers, et al, 2011).
This trend is further corroborated with A2 and B2 IPCC emission scenarios and the ICTP RegCM climate model which state that “by the end of the 21st century the Mediterranean region might experience a substantial increase and northward extension of arid regime lands.”(Giorgi, F. 2008). This threatens to increase water scarcity in downstream states. Arabian Peninsula remain still limited potential for hydroelectric development due to a dearth of rivers, the predicted increase of precipitation in the mountainous regions of Iran will increase flow averages in the Karun River basin. Most of the Middle East stands to lose precipitation in climate change projections, increased precipitation in the Iranian mountains may translate to increased flow and increased hydroelectric potential.
5.5 Africa Africa is heavily dependent on hydropower. South Africa's 42 GW energy accounts around 40 percent of total African capacity (Neil Ford.2007). Due to the dearth of water resources in northern Africa, Sub‐Saharan Africa is home to the majority of the continent’s hydroelectric dams. Most of the generating capacity is concentrated on the continent’s major rivers, the Nile, the Congo, and the Zambezi. However, smaller basins such as the Volta also contain a number of hydroelectric dams
Dominant role in Africa’s electricity portfolio, large projects are planned and under construction in a number of nations including Ethiopia, Uganda, Zambia, Mozabique and Liberiab (Basson, G. 2004). The enormous power potential at Grand Inga has led to discussions of constructing a continent spanning electricity grid that could provide power to all Africans and provide some electricity to Europe and the Middle East. (Wachter, S. 2007; Showers, K.B.; 2009).
Recurring droughts have plagued hydroelectric dams and led to power rationing across the continent. In the past decade, from Ghana to Kenya, Zimbabwe, and Tanzania, droughts have disrupted generation, sometimes reducing plants to half of their capacity. (Mukheibir, P; 2007; Waylen, P. 2008). Differences in temperature and rainfall are projected to be the two biggest impacts of climate change in Africa (but these can also increase evaporation, a crucial consideration for reservoirs (Mukheibir, P. (2007) the rainfall changes will also be different for different sub regions, which raises questions for regional planning and power distribution. While some regions will likely receive more rainfall and thus increased river flows, there is uncertainty regarding the consistency of this increase.
The Congo River Basin is projected to receive both increased rainfall and temperatures, but minimum evaporative reductions to generating capacity due to the humidity of the region and the dearth of reservoir dams (Mukheibir, P., 2007) Other regions face more striking predictions, “Climate models predict an average 10‐20 percent decline in rainfall, resulting in the rivers of Botswana and Tunisia completely drying up. The high‐risk regions include the east‐west bands stretching from Senegal to Sudan.” (Sharife, K. (2009). Harrison and Whittington. (2002) also note that “Simulations indicate that
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for all scenarios annual flow levels at Victoria Falls reduce between 10 and 35.5 percent. In each case the resultant flow change is greater than the precipitation change, confirming the amplifying effect of the hydrology.”
Yamba, et al (2011) conducted a fairly comprehensive study of projected climate change impacts on hydroelectric generation in the Zambezi River Basin. These authors paired hydrologic modelling, based on historical data, with projected climate changes to reveal general trends for the basin and more specific changes for each dam site. Their findings indicate a gradual overall reduction in generation capacity over the next 60 years. Yamba, et al. (2011) However this reduction is only gradual in light of this time scale, as Yamba et al. predict both severely dry years, and potential flooding events. Thus extreme variability must be planned for through strategic management of flows between dams in the basin to maximize generation.
5.6 Asian‐Pacific region There are varying scales of hydropower in the Asian‐Pacific region. Australia maintains the greatest installed capacity with 8,186 MW (Harries, D. (2011). followed by New Zealand (5,373 MW), Malaysia (4520 MW), Indonesia (4,869 MW), the Philippines (3,291 MW), Papua New Guinea (216 MW), and Fiji (85 MW). Energici. (2010).
As much of the region depends on hydroelectric generation, small changes in climate patterns influencing stream flow can have major impacts on overall hydroelectric productivity. Despite the many studies completed in this region, there is still uncertainty in climate change prediction models with respect to precipitation.152 In one study, while an increase in precipitation of 0.1‐9.3 percent was predicted under IPCC A1B scenarios for the Philippines, IPCC A2 climate models predicted precipitation to range from a decrease of 3.3 percent to an increase of 3.3 percent (Combalicer et al, 2010). Varying predictions include increased rainfall during the monsoon season or persistent dry months throughout the year. (Espinueva, S. R. 2010). Some studies predict increased precipitation in south‐eastern Australia (where the majority of hydroelectric production is located), (Hughes, L. L. (2003). while other studies forecast a drier future on average (Chiew et al , 2011). Increase in temperature is projected throughout the region which will increase evaporation and affect stream flows Countries like New Zealand are the most susceptible to conditions of decreased precipitation due to their dependence on reservoir dams with relatively little capacity. Compared to Australian dams, with large‐capacity reservoir dams, most of New Zealand’s dams have little ability to buffer drought conditions.
5.7 Asia The large population of Asia and the expansion of urban areas have caused a rapid growth in electricity demand. But less than a quarter of the continent’s energy comes from hydroelectricity. The vast majority of the electricity, almost seventy percent, is supplied by conventional thermal power plants. Many areas of Asia are incredibly rich in fossil fuels, which encourages the continent to rely on this cheap and readily available energy source (U.S. Energy Information Administration, 2011)
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Nations like Nepal, Bhutan, Pakistan and Tajikistan rely significantly on hydroelectricity (Figure 5.3). The rivers which are utilised for power production are already transforming due to the effects of global climate change. (U.S. Energy Information Administration, 2011). Hydroelectricity comprises the majority of electricity generation in the central Asian countries of Pakistan, Afghanistan, Kyrgyzstan, Tajikistan, Kazakhstan and Uzbekistan. These nations have ambitious plans for expanding their hydroelectric sector, they have already experienced obstacles, both in the form of climactic variability and international tensions.(Steward, Richard. 2010). Many rivers in Asia cross disputed borders, and dam building often heightens existing tensions. These international tensions will likely build as climate change threatens the already limited shared resources.
The majority of hydropower projects in China and the rest of Asia are medium to large scale reservoir dams. However, micro hydropowers are expanding in remote areas of the Himalaya where many communities are not yet electrified (Dhakal, S. 2011). The Himalayan nations of Bhutan and Nepal rely significantly on hydroelectricity generated by the massive change in elevation within their borders. Much of the hydropower produced in Bhutan is sold to India, a neighboring nation. Indeed, the sale of hydropower to India generates over 50 percent of the Bhutanese gross government revenue. Magistad, Mary Kay. (7 July 2011).
Figure 5.3: Asian hydropower dependence. Percent of total installed capacity dedicated to hydropower. Data: US Energy Administration, 2008
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All nations across in Asia are interested in developing their hydropower potential in order to supply their growing energy demands. Some of the most significant plans for expansion are along the Mekong River, which flows through China, Myanmar, Laos, Thailand, Cambodia and Vietnam. Vietnam depends on hydroelectric to produce upwards of 70 percent of its power and neighbouring countries. Laos plans to build more dams on the Mekong River to become the battery of Southeast Asia (Hirsch, 2010). Central Asian countries are also hoping to significantly expand their hydropower capacity to supply both their own burgeoning electricity needs and to increase national funds by selling hydropower to China and Pakistan (Peyrouse, S. 2007). Nepal appears determined to expand her hydroelectric sector, hope to be a battery for North India and Bangladesh, but political instability and regional mistrust is breaking speedily development. The Chinese already regulate their dams along the Mekong River to produce a steady amount of electricity, but doing this causes downstream wet season flooding and dry season water shortages, problems which will likely be compounded by changes in the monsoon pattern. (BBC, 2020) Unpredictability, surges in river flows, and water shortages are all linked to climate change induced alterations to the South Asian monsoon.
Asia has already experienced disasters related to climate change which are often compounded by poor land‐use practices. The most recent of extreme weather events is the massive flooding in Thailand during the fall of 2011. Scientists believe this monsoonal deluge can be linked to climate change (The Guardian 1 Nov. 2011). The 2010 floods in Pakistan affected over 20 million residents and inundated 62,000 square miles of the country. Scientists have also linked these floods to monsoon rains intensified by climate change (Doyle, A, 2010) Many areas of Southeast Asia receive up to 80 percent of their annual rainfall during the summer months making the rivers highly variable during the monsoon season(Reuters, 27 Feb, 2009). Rising temperatures might affect monsoon to arrive later in the year, lengthening the time between rains and increasing the region’s vulnerability to drought, especially during the summer growing season. Scientists predict that Climate change will certainly have implications for the viability of hydropower in the region.
Droughts have also plagued Asia. Poor water management combined with climate change has spurned some of the most severe droughts in the continent’s history. In 2004, the Yunnan Province of China underwent one of the worst droughts in years, experiencing 60 percent less rainfall and leaving 8.1 million residents short on drinking water ( Qiu, J.,2010). Almost simultaneously, another heavy monsoon caused catastrophic flooding in Bangladesh, India, Nepal, Vietnam and other areas of China (The Guardian, 2004). Since the 1960s, the number of overall rainy days has decreased in China, while the number of extreme precipitation events has increased ( Qiu, J. 2010). Climate change has caused the temporal distribution of water resources to become more unpredictable in Asia (McNally, A.,2009). The unpredictability and volatility in precipitation across the continent naturally affects hydropower generation. Though it is difficult to predict the future impacts of climate change, it is certain that climate change will significantly affect Asia not only because of its ecological qualities and geographic location, but also because many Asian nations lack the infrastructure and resources to effectively respond to crises spawned by climate change.
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The Himalayan glaciers hold the largest store of fresh water outside the Polar Ice Caps. Many of the rivers on the Asian continent originate in the Himalayas. Steady glacial melt has fed these rivers, regulating their flow throughout the annual hydrological cycle. However, many of these glaciers are rapidly melting, causing yet more volatility in the flow levels of rivers in Asia. Though intensified glacial melt increases the flow level of the rivers they feed, rapid spring melting causes a shortage in late season flows (Ives, M. (2011), when water is often critical for agriculture. Deglaciation in the Himalaya will also cause rapid growth of glacial lakes, which will increase the likelihood of glacial lake outburst floods. These devastating and often unexpected floods could wreak havoc on hydroelectric infrastructure. The deglaciation pattern will deliver water to the rivers in sporadic bursts rather than a steady stream of flow. Glacial melt will cause initial overall increased flow for the rivers originating in the Himalaya. However, highly variable river flow is not optimal for hydropower, so even though deglaciation will increase the flows at certain periods of time, its variability and unpredictability make hydropower more vulnerable on rivers. Some smaller rivers are fed exclusively by glacial melt, and could dry up in as few as 50 years. This naturally would affect downstream hydropower, not to mention the water supply of communities along such rivers.
6. Major River Basins of Nepal Nepal, a country of mountains and hills and sandwiched between India and China, lies in South Asia. Eight peaks out of ten worlds’ highest mountain peaks including Mount Everest are in Nepal. Altitudinal variation ranges from about 80 to 8848 meters above sea level (Figure 6.1) from in a span of only about 200 kilometres.
Ecologically Nepal can be divided into lowland, midland and highland regions. Mountains and hills occupy about 80 % of the total national land (Table 6.1). The elevation differences favored for a variety of biomes from tropical savannas along the Indian border to montane grasslands and shrublands and tundra along rock and ice at the highest elevations. These ecological belts run east-west and are vertically intersected by Nepal's major, north to south flowing river systems.
Figure 6.1: River system and North‐South Topographical difference
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Table 6.1: Geographic regions of Nepal
Source: CST Nepal, 1997
Nepal contains about 2.27 of the world’s water resources (DHM, 1998). There are more than 6000 rivers in Nepal out of which about 54 rivers are each longer than 150 kilometres and 964 rivers are each longer than 10 kilometres( DHM,1998) The total length of each stream exceeds 45000 Kilometres giving drainage density to about 0.3 Km per sq. km. Karmali in the west, Gandaki in the Central and Kosi in the east are three main river basins of Nepal. About 78% of the mountainous part and about 70% of the Nepal territory is drained by these three rivers. Only a very small portion of watersheds of these rivers lie in Tibet, China. Mahakali river basin is a sub basin of Karnali river and lies in India and Nepal. The other major sub basins that do not contain year round snow covered zones are Babai, Rapti, Bagmati, Kamala. Kankai and Mechi river catchments.
Broadly, Nepalese catchments fall on three river groups. The group grading is based on the river discharge and their sources.
6.1 First Grade Rivers Rivers that are originated from glacier on ice caped mountains above the snow line are categorized as the first grade rivers. These rivers are perennial and carry sufficient flows in all seasons. Karnali river in the western region, Gandaki river in central region, and Kosi river in the eastern region as well as their tributaries which originate from glaciers are categorized as the first grade rivers. Kaushiki (Kosi) is also called as Saptakosi from Barahachetra at Chatara. Sapta means seven in Sanskrit. Seven Kosi are Tamur, Arun, Dudh, Tama, Sun, Likhu and Indrawati. Similarly, Gandaki is called as Narayani from Devghat at Narayanghat. Narayani is also is called Saptagandaki and seven Gandaki are Trishuli, Budhi, Daraudi, Marhsyandi, Seti, Kali and Myagdi. Modi of Kali, and Madi of Seti are also other major tributaries that have sources in Snow and Glaciers. Narayani is again named as Gandak in India. Likewise, Humla, Mugu, Seti, Tila, Thulo Bheri, Sano Bheri and Bhudiganga are the main tributaries of Karnali river. Karnali is called as Ghagra in India. Mahakali is the border river between Nepal and India. Chameliya and Surnagad are two major tributaries of Mahakali coming from Nepal. Saryu, Gauriganga and Dhauliganga are major tributaries coming from India. Mahakali is called as Sharada in India.
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6.2 Second Grade Rivers They are originated from Mahabharat hills. Mahabharat hills fall below the snow line thaties at about 5000 meters altitude. They also do not dry up in the low flow period as they meet spring and shallow underground water tables. Mechi river, Kankai river, Kamala river, Bagmati river, East Rapti river, Tinau river, West‐Rapti river, Babai river are second grade rivers. West‐Rapti river is the biggest amomg them. East Rapti river basin falls totally in Nepal. Others have their confluence point in India. Roshi Khola (a tributary of Sunkosi), Trijuga (a tributary of Saptakosi), Andhi Khola and Ridi Khola (tributaries of Kali Gandaki) lie in the mountainous region below 5000 meter altitude.
6.3 Third Grade Rivers Rivers that are originated from Siwaliks hills as well as from the Tarai plain are to be understood as the third grade rivers. These rivers contain either very less water in the winter or no surface flow in the dry period. Examples of such rivers are Banganga at Rupandhehi, Tilawa at Parsa, Vangori and Sirsia at Bara, Manusmara at Sarlahi, Hardinath at Mahotari, Sunsari at Sunsari and so on. They are originating in Siwaliks and flow through Tarai in the plain.
Over 6000 Nepalese rivers, most headwater of snow and glacier fed stream are perennial where as some of head water of non snow fed rivers fall on intermittent type. Most of rivers on lower siwalik are ephemeral. Ephemeral rivers are rivers that do not always flow, that is, they dry up and are seasonal. How often, and for how long they dry up varies depend on the watershed characteristics and meteorological pattern like deserts and dry climates. An intermittent river only flows occasionally and can be dry for several years at a time. These rivers are found in regions with limited or highly variable rainfall, or can occur because of geologic conditions such as having a highly permeable river bed.
7. Hydropower Potential in Nepal Having steep gradients, Nepalese rivers, fed by snows possess high hydropower potential. An assessment made by Dr. Hariman Shrestha indicated that Nepal have it a potential of 83000 Mega Watt. But in the present context hydroelectricity potential of Nepal could exceed.
Nepal had its first hydropower electricity project run in 1911 (1968 B.S. Nepal Era). Pharping hydroproject, which was the first hydropower project in Nepal located some kilometres south of Kathmandu had a capacity of 500‐kilowatt capacity. Since then, Nepal could produce only about 600 Mega Watt (MW) only. Government of Nepal introduced BOOT (Build, Own, Operate and Transfer) policy for hydropower development since year 1950. Till January 2010, licenses issued and application received amounted to more than 60000 MW. The largest capacity project indentified are Mahakali rivers at Pancheswor (6000 MW) and Karnali River at Chisapani (10500 MW). Hence, hydropower production of Nepal would bring an economic revolution in Nepal if high dam concept is materialized with neighboring countries especially with India and Bangladesh. Hydropower projects in Nepal are divided into micro, small, medium and large. The total capacity of the projects under NEA and IPP up to June 1, 2012 is summarized in Table 7.1
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Table 7.1: Hydropower Potential of Nepal (identified 1 June, 2012)
Category Number of sites Total Capacity (MW)
Construction License for Generation
1 to 12 MW 16 317
Application for Construction License for Generation
upto 127 MW 51 3474
Cancelled Construction License for Generation
5 to 14 MW 3 24
Survey License for Generation
Below 1 MW 202 149
1 to 25 MW 178 1099
25 to 100 MW 51 2730
Greater than 100 MW 29 8510
GON Reserved Survey License for Generation
2 to 1110 MW 42 3456
Application for Survey License for Generation
Below 1 MW 806 682
1 to 10 MW 480 2332
194 20803
Cancelled Survey License for Generation
upto 96 MW 41 516
Total 2093 44092
(Source : www.doed.gov.np)
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Private sectors contribution is 174 MW out of 700 MW of total production of Nepal. Latest updated information made available by Nepal Electricity Authority at its annual report is given in Table 7.2 below:
Table 7.2: Existing power plants run by private companies.
Energy demand is increasing annually. Demand forecast made by NEA is given in Table 7.3 below’
Table 7.3: Load Forecast for Nepal
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Figure 7.1: Load Forecast [Source: Nepal Electricity Authority, A YEAR IN REVIEW, FISCAL YEAR 2010/11]
The systematic collection of hydrological data began in 1962‐65 by UN special fund and USAID fund for a feasibility study of hydro power project and hydrological services. Department of hydrology and meteorology has been publishing stream flows records. Availability of water and trend in river flows for selected rivers ‐ Snowfed and non snow fed river is presented below
8. Climate change in Nepal Temperature and precipitation observation history is not long enough to draw any conclusion in Nepal. Analysis carried out by some scientists/researchers had assessed climate changes and impacts the warming was consistent and continuous after themid‐1970s. Climate change is a matter of global concern. It is predicted that one degree temperature raise at sea level will correspond to two degree temperature raise in high altitude region like Himalaya (IPCC, 2001). Spatial variation of the annual mean temperature trend analysis showed the increasing trend in almost entire country except on few isolated places (Karmacharya etal, 2007, Practical Action 2009).) The mean temperature of basin has a rising trend by about 0.02 per year (Baidya etal, 2008). The average annual rainfalls in the basin and on overall western regions of Nepal have a positive trend (Baidya etal, 2008). Lower part of Kaligandaki basin area from where rain shadow starts and which is the wettest part has an increasing trend in annual precipitation with the rate of about 0.70 millimeter per decade (Gauchan A. 2010) where as the
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northern part of the basin which is the lowest precipitation region has been experiencing decreasing trend in snowfall.
8.1 Trend in Changes in average annual maximum temperature It was found that the average warming in annual maximum temperature between 1977 and 1994 was 0.06 degree Celsus per year (Shrestha et al. (1999). Warming was seen more pronounced in the higher altitude regions of Nepal such as the Middle Mountains and Himalaya, while the warming happened significantly lower, or even lacked, in the Terai and Siwalik regions. Warming in the winter was more pronounced compared to other season (Table 8.1).
Table 8.1 : Regional mean maximum temperature trends for the period 1977–1994 (degree C/year)
[Source Shrestha et al. 1999]
8.2 Trend in precipitation The Indian Institute of Tropical Meteorology (IITM) had high resolution climate scenarios for the South Asian region from the regional climate model PRECIS (HadRM3) for emission scenarios SRES‐A2 and B2 (Rupa Kumar et al. 2006). These scenarios indicate a decrease in monsoon in the northern parts of the country and increase in the southern parts (Figure 8.1).
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Figure. 8.1: Projections of changes in monsoon precipitation (top) and average annual temperature (bottom) by the end of the twenty‐first century for emission scenario SRES‐A2 (left) and B2 (right) (Rupa Kumar et al. 2006)
Nepal may get warming on average by 3.5–4 degree Celsius in those scenarios at the end of the century. The IPCC AR4 has indicated that the warming in South Asia would be at least 2–4 degree Celsius by the end of the century (Christensen et al. 2007). The warming rates follow the elevation gradient in the Himalayan region (e.g.,Bhutan, Nepal, and Himachal Pradesh). The projection for Nepal was also made by selecting the SRES B2 scenario by using the MAGICC/SCENGEN model (Agrawala et al. 2003) . This analysis also showed somewhat larger warming in winter months than the summer months., The projected warming above the baseline average (1961–1990) is 1.2 degree Celsius for 2030, 1.7 degree Celsius for 2050 and 3.0 degree Celsius for 2100 (Table 8.2).
Table 8.2: GCM Estimates for temperature and precipitation changes in Nepal
(Source: Agrawala et al. 2003)
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Trend analysis on observed data rainfall and temperature was performed. It was confirmed that there is a rising trend of temperature in Nepal. Annual rate of temperature rise was found to be about 0.41o C per decade. Trend on precipitation was decreasing at the rate of 9.8mm/decade in the month of April and May though, a rising trend of precipitation was observed during monsoon seasons.
Trends of monsoon onset and withdrawal from 21 years of data show that monsoon season is elongating in both the ends. Onset will occur earlier by 71 % of a day per annum and withdrawal will retreat by about 15 % of a day per annum. Although this trend appears to be elongating monsoon period for long, it is not likely to happen due to changes of seasons. In case of trend of withdrawal of monsoon it is not so distinct whereas trend of monsoon onset is quite distinct.
8.3 Climate change induced trend in Rainfall and Temperature
8.3.1 Rainfall As the inter‐annual variation of rainfall is so large, no significant trend like in temperature could be observed. However, the general tendency towards increasing or decreasing trend is more important in rainfall. Rainfall trend analysis showed the positive trend in most of Eastern, Central, Western and Far‐western Development Regions in annual rainfall. However, most of the Mid‐western Development Region showed the decreasing annual rainfall trend. The region in and around Dolakha district observed the largest decreasing trend of up to ‐40 mm/year (Figure 9.1). Trend analysis of pre‐monsoon rainfall showed increasing trend in most of the Eastern, Central and Western Development Regions, while Mid‐western and Far western Development Regions showed the decreasing trend (Figure 9.2). The highest increasing trend for the pre‐monsoon rainfall was observed in and around Myagdi and Kaski districts in the Western Development Region; Sindhupalchowk district in the Central Development Region and Sankhuwasabha in the Eastern Development Region, however some small pocket areas in these regions showed the decreasing trend e.g., Dhankuta, Dolakha, Ramechhap and Tanahun with the largest decreasing trend in the north western parts of the country. Monsoon season rainfall was observed to be mainly increasing in the Eastern, Central, Western and Far‐western Development Regions while most of the areas in Mid‐western Development region showed the decreasing trend the highest trend in Dolakha and Solukhumbu districts (Figure 9.3). Monsoon season contributes about 80 % of the total annual rainfall. The rainfall trend in post‐monsoon season showed the increasing trend in most of the Mid‐western Development Region and the southern parts of Eastern, Central and Western Development Regions while Far‐western Development Region and most of the northern parts of the country observed the decreasing trend (Figure 9.4). With the highest increasing trend in Sankhuwasabha, Taplejung and Accham districts, winter season rainfall showed increasing rainfall trend almost over the entire country. However, some areas in the northern parts of Mid‐western and Eastern Development Regions and some isolated small pocket areas here and there showed increasing trend (Figure 9.5). Though seasonal rainfall is less in southern parts; Siwalik and the Terai, the highest 24 hour rainfall is recorded in these parts (Figure 8.6). The highest extreme rainfall was found mainly in the foothills of Mahabharat and
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Siwalik in the Central Development and Western Development regions. These regions are therefore prone to flash flood and inundation.
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Figure 8.5: Winter rainfall (mm/year) trend Figure 8.6: 24 hour’s highest rainfall (mm)
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8.3.2 Future Projection on Rainfall trend
Precipitation projection under high (A1), medium (A1B) and low (B1) GHG emission scenarios for 20’s (2010‐2030), 50’s (2040‐2060), 80’s (2070‐2090) showed increased precipitation in the entire Nepal.
B1 Scenario
For this scenario, the ensemble averaged precipitation change shows more or less consistent pattern (Figure 9.7) for all three future periods ‐1920,1950, and 1980. Precipitation is projected to increase in the entire Nepal during all time span (20’s, 50's and 80's). Larger increase in precipitation is projected over Western Region with up to 60 mm and 80 mm increase per annum respectively during 20's and 50’s. Since high precipitation and flood/ landslide are directly related, any significant increase in precipitation as projected over these areas will increase the likelihood of flood and other related hazards.
Figure 8.7: Mean annual Change in precipitation (in millimeter) for B1 scenario (a) 2020's (b)
2050's (c) 2080's
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A1B Scenario
The ensemble averaged precipitation change shows more or less consistent pattern compared to B1 scenario (Figure 8.8) for all three future periods. Precipitation is projected to increase in the entire Nepal during all time spans. Largest increase in precipitation is projected over Western Region upto 70 mm during 20’s, 140 mm over Eastern, Central and Western Regions during 50’s and upto 250 mm in Eastern Region during 50’s ( Figure 8.8).
Figure 8.8: Mean annual Change in precipitation (in millimeter) for A1B scenario (a)
2020's (b) 2050's (c) 2080's
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A2 Scenario
The ensemble averaged precipitation change shows more or less consistent pattern (Figure 8.9) compared to previous two scenarios for all three future periods but there is subtle variation for 20's. Precipitation is projected to decrease by up to 20 mm over Far Western Region and southern parts of Eastern Region. Pattern for 50's and 80's quite consistent for A2 scenario in comparison to B1 and A1B scenario with increase up to 100 mm and 200 mm over Eastern Region respectively( Figure 8.9)
Figure 8.9: Mean annual Change in precipitation (in millimeter) for A2 scenario (a) 2020's (b) 2050's (c) 2080's
Table 8.3 shows the projected change for temperature and precipitation under different scenario averaged over Central Himalayan region that covers Nepal and adjacent areas. In case of temperature the projected increase is slightly higher than that averaged over South Asia. It ranges from 1.1C to 1.3C in 2020's, 1.8C to 2.5C in 2050's and 2.5C to 4.2C in 2080's among the three scenario. In case of precipitation the projected changes are in line with that average over South Asia.
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Table 8.3: Projected change for temperature and precipitation under different scenario averaged over Central Himalayan region
9. CLIMATE Change impact in River flows pattern in Nepal
9.1 River Flows Pattern The key elements for hydropower project are the flow available for its use. Any change in flows caused changes in the production of electricity. The systematic collection of Hydrological data began in 1962‐65 by UN special fund and USAID fund for a feasibility study of hydro power project and hydrological services. Department of Hydrology and Meteorology has been publishing stream flows records since 1963/64. Based on published data, trend in flows trend in selected rivers is determined (Figure 10.1). Selected rivers are of two categories ‐ Snowfed and nonsnow fed river. Non snow fed category are basically rain fed rivers whose sources lies around 3000 meters.
Figure 9.1: Location of three major rivers system, Kosi, Narayani and Karnali
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Trend in annual discharge and annual fluctuation in mean annual flows was assessed on data published by DHM. There is as light positive trend i.e. increasing trend in Koshi river flows. But this trend is insignificant compared to the percent difference in annual mean to the long term mean. Koshi flows found appreciable increased after 1998/99 and in some years difference reaches to 30 percent increased. Tributaries flows also have similar nature but amount deviation and trend is different. Deviation in Tamur crossed 50 percent in particular wet year (Figure )
Narayani river basin showed a slight increase in annual flows. The percent difference is relatively lower than Koshi basin. In most of the year, difference fall below 10 percent. Differences in annual mean is about 20 percent. Wet and dry year flows. Chepe river, a tributary of Marsyangdi river within the Narayani basin also showed an increasing trend. There is positive trend in Karnali river flows. This river flow is relatively stable compared to Koshi and Narayani. Difference in annual means is about 20 percent.
Similarly, trend in annual mean flows of non snow fed rivers – Kankai, Bagmati, lother‐Manahari, West Rapt and Babi ( Figure also do not show any significant trend. However, there are significant trend monthly flows. Winter flows are in decreasing trend where as annual extremes are increasing represent partly the result of warming trend in the region due to climate changes.
Koshi river: Combination of Monsoon and Snow fed rivers in Eastern Region
Figure 9.2 : Trend in mean annual discharge of Kosi Figure 9.3: Annual flows deviation in Kosi
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Tamur river :
Figure 9.4 Trend in mean annual discharge of Tamur Figure 9.5: Annual flows deviation in Tamur
Narayani : Combination of Monsoon and Snow fed rivers in Central Region
Figure 9.6: Trend in mean annual discharge of of Narayani Figure 9.7: Annual flows deviation in Narayani
Chepe river
Figure 9.8: Trend in mean annual discharge of Chepe Figure 9.9: Annual flows deviation in Chepe
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Karnali river : Combination of Monsoon and Snow fed rivers in Western Region
Figure 9.10: Trend in mean annual discharge of Karnali Figure 9.11: Annual flows deviation in Karnali
Chamelia river
Figure 9.12: Trend in mean annual discharge of Chamelia Figure 9.13: Annual flows deviation in Chamelia
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Kankai river: A Non snow fed river in in Kosi –Mechi basin in Eastern Nepal
Figure 9.14: Trend in mean annual discharge of Kankai Figure 9.15: Annual flows deviation in Kankai
Bagmati river: A Non snow fed river in Central Nepal
Figure 9.16: Trend in mean annual discharge of Bagmati Figure 9.17: Annual flows deviation in Bagmati
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Lother and Manahari: A Non snow fed river in Central Region
West Rapti: A Non snow fed river in Karnali and Rapti basin in Western Nepal
Figure 9.20: Trend in mean annual discharge of W Rapti Figure 9.21: Annual flows deviation in W Rapti
Figure 9.18: Trend in mean annual discharge of Lothar and Manahari river
Figure 9.19: Percent difference in mean annual flows with longterm of Lothar and Manahari i
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Babai: A Non snow fed river in Karnali and Rapti basin in Westen Nepal
Figure 9.22: Trend in mean annual discharge of Bagmati Figure 9.23: Annual flows deviation in Bagmati
9.2 The effect of climate change in Nepalese river flows The effect of recent climate changes on river flows are not yet done extensively. The general perception is made on trends in three categories as large outlet rivers, southern rivers and snow‐fed rivers. Among the large rivers, Karnali and Sapta Koshi show a decreasing trend, Narayani (Kali Gandaki), shows an increasing trend. Southern rivers do not show any trend. All of the three snow‐fed rivers examined here show a declining trend in discharge. Preliminary trend analysis on observed records indicated that discharge trend is neither consistent nor significant in magnitude. It could be due to short record lengths and high inter‐annual variability in discharge data. Another study indicated that the number of flood days and consecutive days of flood events appeared to be increasing (Shrestha and Shrestha 2003).
The Himalayan Rivers are vulnerable to climate change. The degree of sensitivity may vary among the river systems. The magnitudes of snowmelt floods are determined by the volume of snow, the rate at which the snow melts and the amount of rain that falls during the melt period. The peak melting season in the Himalayas coincides with the summer monsoon rainfall, which contribute to increased summer runoff and flood disasters (IPCC, 2001b, p.565). The increase in temperature would shift the snowline upward, which reduces the capacity of natural reservoir.
The annual runoff of the Alkananda River in the western Himalayas increased by 2.8% yr‐1 for 1980‐2000, whereas that of Kali Gandaki River in Nepal Himalayas increased by about 1% annually for 1964‐2000 (Shrestha, 2005). A runoff sensitivity analysis by Mirza and Dixit (1997) showed that a 2ºC rise in temperature would cause a 4% decrease in runoff, while a 5ºC rise in temperature and 10% decrease in precipitation would cause a 41% decrease in the runoff of the Ganges River near New Delhi. As the snow and glacier volume gets smaller and the volume of meltwater reduces, dry season flows will decline to well below present levels (Shrestha, 2005, p.77). River discharge is influenced by climate, land cover and human activities, so it is difficult to disaggregate the climatic impact from non‐climatic impacts on river discharge. However, river discharge analysis for 1947‐1994 in the Kosi Basin in eastern Nepal showed a decreasing trend particularly during the low‐flow season.
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Sensitivity analysis of river runoff in the same basin showed that the runoff increase was higher than the precipitation increase assuming temperature constant and an increase in temperature of 4°C assuming precipitation constant would cause a decrease in runoff by two to 8 percent (Sharma et al., 2000b, p.139). Gurung (1997, p.37) has revealed that there will be decrease in runoff in dry seasons and increase in runoff in monsoon season under the doubled CO2‐scenario using the Canadian Climate Centre Model (CCCM) and Geophysical Fluid Dynamics Laboratory (GFDL) models
The assessment made on Upper Kaligandaki river basin. The basin also lacks longtern data on stream flows. The important of the basin lies in the fact that streams within the basins get water sources as snow and glacial melt. The basin lies in the rain shadow area where only about 150 to 250 mm of precipitation is reported from observed record. An assessment indicated that the snow melt contribution (Figure 9.24, Figure 9.25) could reach up to 40 % (Bhusal J K & Sagar P, 2011). The worst scenarios as per the present projection are that future flow characteristics of snow fed rivers could appear to be like that of present pattern of non‐snow fed rivers. And the reduction in river flows in the basin could be up to 40 % if all snow dries up. However, the situation would be more miserable if temporal and spatial variations become wider due to climate changes in future.
Figure 9.24: Annual runoff and rainfall volume Figure 9.25: Flow recession curves
10. Climate Change as it affects in Hydropower Production The slight increase in temperature paired with an increase in precipitation suggests that the evaporation rates of the region will decrease slightly. The overall increase in precipitation will provide more water to the rivers, increasing the potential for hydropower generation. The increasing temperature in the Himalayas will increase the glacial melt that feeds the rivers, increasing discharge for at least the next several decades. However, once these glaciers have melted, there will be a decline in river’s discharge. South Asia’s climate and hydrological cycles are significantly impacted by the monsoon, which has already been altered by climate change (Science Daily, 2009). The monsoon delivers around 75 percent of the regions precipitation during roughly three months. The beginning of the monsoon is predicted to arrive later in the year, making the dry season longer and increasing the number of droughts (Science
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Daily, 2009). Similarly, there will be an increase in the severity of rainfall events as well as storms, causing overall increased temporal variability in water supply (McNally, A. 2009). The disparate distribution of precipitation timing in this area causes significant variations in the Mekong River’s discharge. All of these various climate change impacts are interconnected and have significant repercussions for hydropower. As climate change impacts intensify, this variation will be exacerbated, making it more difficult for hydropower facilities along the Mekong River to predict river discharge and to generate an even supply of power.
10.1 Hydropower and Impact of Climate in Snow and Glacial areas Agrawala et al (2003) has also identified two critical impacts on water resources in Nepal due to climate change – GLOFs and variability of river runoff. These posed significant impacts not only on but also on rural livelihoods and agriculture but also on hydropower. Micro‐hydro, for example, serves multiple rural development objectives. They have indicated that the water storage might be a potential adaptation to response to increased variability in stream‐flow and reduced dry season flows for sustainability of forecasted energy output from hydro projects. But there is also a risk of environmental objectives that might conflict with large storage projects. Dams could potentially exacerbate vulnerability to another potential impact if breached. Trans‐boundary or regional dimension to certain impacts also demands need for regional coordinated strategies to cope with impacts of climate change.
The scoring for following four factors is made. In ranking the risks from climate change, was considered, Impacts that are most certain are ranked as the most severe, and most likely to become severe in the first half of the 21st century are ranked the highest. The results (Agrawala et al ,2003) of this analysis are summarized in Table 10.1
Table 10.1:. Priority ranking of climate change impacts for Nepal
A study by WWF (2009) has predicted climate change responses to Koshi River and its major tributaries. The energy budget model simulations on the snowmelt in conjunction with comprehensive catchment model were applied in Koshi basin that has significant snow and glacier coverage. Ice ablation from the debris covered glacier area has a remarkable influence over the river discharge. The results of simulations showed significant impact on stream flows. The contribution of snow and glacier melt discharge to annual flow River flow at a station ‘Chatara’, from where river enters plain area of Nepal
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Tarai, is about 8.46% (WWF 2009) A maximum monthly contribution of 22.52% is in May and a minimum monthly contribution of 1.86% is in January. 2.51% out of total 8.46% snow and glacier melt contribution is from Dudh Koshi sub‐basin (WWF 2009). This basin has maximum contribution to annual flow at Chatara. Arun and Tamor basins are two other major tributaries, Tamor, Arun and Dhudha Kosi share 84% Kosi flow at Chatara. Indrawati sub‐basin has minimum contribution to annual flow at Chatara (0.15% out of total 8.46%). (WWF 2009). Sensitivity test of snow and glacier melt contribution was carried out for increase in air temperatures of 0.020C, 0.040C, 0.080C and 0.120C. The results of the simulation for these scenarios are presented in Table 10.2.
Table 10.2: Annual snow and glacier melt contribution (in %) for increased temperature scenarios
Station Name Increase in Temperature (ΔToC)
0.00 0.02 0.04 0.08 0.12
Indrawati (Dolalghat)
3.66 3.66 3.67 3.68 3.72
Sunkoshi (Dolalghat) 3.56 3.57 3.59 3.61 3.66
Busti 7.55 7.57 7.58 7.61 7.69
Khurkot 3.80 3.81 3.82 3.84 3.89
Sangutar 8.96 8.98 9.03 9.10 9.17
Rabuwa bazar 16.37 16.39 16.49 16.58 16.63
Kampughat 7.85 7.86 7.90 7.95 8.00
Uwagaon 14.92 14.98 15.08 15.32 15.45
Turkeghat 9.45 9.48 9.55 9.71 9.80
Majhitar 17.91 17.94 18.03 18.15 18.21
Mulghat 8.84 8.86 8.91 8.97 9.01
Chatara 8.46 8.48 8.53 8.61 8.66
(Source: WWF 2009)
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Table 10.3: Contribution (%) of glacierized sub‐watersheds of each sub basins to the total flow at downstream stations
Sub‐basins Indrawati Sunkoshi
Tama koshi
Likhu Dudh koshi
Arun Tamor Overall Contribution Station Name monthly
Indrawati (Dolalghat)
max 28.80
‐ ‐ ‐ ‐ ‐ ‐
28.80
min 1.83 1.83
annual 3.66 3.66
Sunkoshi (Dolalghat)
max
‐
7.70
‐ ‐ ‐ ‐ ‐
7.70
min 2.36 2.36
annual 3.56 3.56
Busti
max
‐ ‐
17.78
‐ ‐ ‐ ‐
17.78
min 5.17 5.17
annual 7.55 7.55
Khurkot
max 1.28 3.11 5.80
‐ ‐ ‐ ‐
9.99
min 0.30 0.78 1.34 2.43
annual 0.46 1.25 2.09 3.80
Sangutar
max
‐ ‐ ‐
36.68
‐ ‐ ‐
36.68
min 1.64 1.64
annual 8.96 8.96
Rabuwa bazar
max
‐ ‐ ‐ ‐
74.01
‐ ‐
74.01
min 3.93 3.93
annual 16.37 16.37
Kampughat
max 0.96 2.19 4.32 1.30 17.77
‐ ‐
24.40
min 0.20 0.53 0.90 0.14 0.97 2.95
annual 0.30 0.80 1.33 0.37 5.05 7.85
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Uwagaon
max
‐ ‐ ‐ ‐ ‐
25.88
‐
25.88
min 0.90 0.90
annual 14.92 14.92
Turkeghat
max
‐ ‐ ‐ ‐ ‐
19.15
‐
19.15
min 0.93 0.93
annual 9.45 9.45
Majhitar
max
‐ ‐ ‐ ‐ ‐ ‐
31.97 31.97
min 2.73 2.73
annual 17.91 17.91
Mulghat
max
‐ ‐ ‐ ‐ ‐ ‐
26.40 26.40
min 1.80 1.80
annual 8.84 8.84
Chatara
max 0.35 0.81 1.61 0.48 8.54 4.68 7.28 22.52
min 0.08 0.24 0.38 0.06 0.37 0.38 0.37 1.86
annual 0.15 0.40 0.66 0.19 2.51 2.20 2.36 8.46
(Source: WWF 2009)
Hydropower are rank significantly higher than any other sector because river flows are directly related to rising temperatures that have already been observed, and are projected (with high confidence) to increase further over the coming decades. This enhances glacier retreat that in turn causes greater variability in stream flows. Dark side of glacial lake outburst floods is that floods pose significant risk to hydropower facilities, and also to other infrastructure and human settlements.
Other climate induced risks to water resources and hydropower facilities include: flooding, landslides, and sedimentation from more intense precipitation events (particularly during the monsoon), as well as greater unreliability of dry season flows that poses potentially serious risks to water and energy supplies in the lean season.
Intense precipitation events, increased floods, landslides, and sedimentation (particularly during the monsoon) are expected to result from climate change. Hydropower infrastructure and facilities are at risk. Hydroelectric plants are highly dependent on predictable runoff patterns, Greater unreliability of dry season flows, in particular, poses potentially serious risks to hydro electricity energy production in
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the lean season. In addition, uncertainties in climate projections and lack of reliable hydrological records are a constraint for effective planning and operation of a hydropower. .
10.2Consequence of Climate Change to Infrastructure A nearly completed Namche Hydropower Project was washed away by Dig Tsho Glacier Lake outburst flooded on 4 August 1985 in the Langmoche valley, Khumbu (Ives 1986; Yamada 1998). The lake, crescent in shape, was dammed by a 50 m high terminal moraine. The GLOF was caused by detachment of a large ice mass from the upper portion of the Langmoche glacier during clear weather condition in July. The ice mass overran the glacier and splashed into lake which was already full. Since then, Government of Nepal (GON) has considered GLOFs as a threat to the development of water resources of the country and has realized the necessity to carry out studies on glaciers and GLOFs.
An preliminary investigation said that there are 2,315 glacier lakes of different sizes in Nepal and the total area of which is 75 km2. (ICIMOD/UNEP2001). Due to warming climate, the melting process is accelerated. Retreated glacier area has a large void as the depression that was earlier occupied by glacial ice. The moraine walls that act as dams are structurally weak and unstable and undergo constant changes due to slope failures, slumping, etc. and are in danger of catastrophic failure, causing glacier lake outburst floods (GLOFs).
Moraine dam do break as self‐destruction or by trigging action of some external forces. Self‐destruction is caused by the failure of the dam slope and seepage from the natural drainage network of the dam A huge displacement wave generated by rockslide or snow/ ice avalanche from glacier terminus into the lake may cause the water to overtop the moraines, create a large breach and eventually cause the dam failure (Ives 1986). Earthquakes may also be one of the factors triggering dam to break, however breaking also depends on its magnitude, location and characteristics of lakes.
A GLOF cause devastating consequences for riparian communities, hydropower stations and other infrastructure. Some past disastrous GLOF events in Nepal are shown in Table 10.4 below.
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Table 10.4: List of GLOF events recorded in Nepal
Date River Basin Name of Lake 450 Years ago Seti Khola Machhapuchchhare August, 1935 Sun Koshi Taraco, Tibet 21 September, 1964 Arun Gelaipco, Tibet 1964 Sun Koshi Zhangzangbo, Tibet 1964 Trishuli Longda, Tibet 1968 Arun Ayaco, Tibet 1969 Arun Ayaco, Tibet 1970 Arun Ayaco, Tibet
3rd September, 1977 Dudh Koshi Nare, Tibet
23rd June, 1980 Tamur Nagmapokhri, Nepal
11th July, 1981 Sun Koshi Zhangzagbo, Tibet
27th August, 1982 Arun Jinco, Tibet
4th August, 1985 Dudh Koshi Dig Tsho, Nepal
12th July, 1991 Tamo Koshi Chubung, Nepal
3rd September, 1998 Dudh Koshi Sabai Tsho, Nepal
In the past few decades, global climate change has had a significant impact on the high mountain environment: snow, glacier and permafrost are especially sensitive to changes in atmospheric condition because of their proximity to melting conditions. The formation and growth of glacier lakes is linked to deglaciation resulting the appearance of ponds. Due to warming climate, ponds grow bigger and merge. This relationship between climate change and its impact over supra‐glacier and GLOF will be explicitly studied in the proposed area by taking past data.
11. Conclusions, Adaptations and Policy Recommendations Himalayan region is severely affected by global warming (I1PCC 2007). Whether the present rate of temperature rise will continue or will show some discrepancies/stability in future remain to be verified. The degree of climate variability that is described by the differences between long‐term statistics of meteorological elements calculated for different periods is the measure of climate change. There are variations
in predictions. The variation in model outputs is believed due to the smaller hydrometereological observation network and short data series (Soito, J. L., Freitas D. S. 2011). However, the rise in
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temperature cannot be expected to be linear over the time. The global cry to reduce green house gases to a certain levels is expected to place the risk at adaptable limit.
The effect of climate changes, though not exactly quantified, is visualized to be heterogeneous over different ecological zones of Nepal. Certain areas especially higher Himalayas of Nepal are becoming increasingly susceptible to hydrological transformations caused by climate change. Research on climate, climate change and its impacts on different sectors are very limited in Nepal. Observed climate data are not sufficient to carry out intensive research. Common understanding of climate change is the change in rainfall and temperature pattern in specific areas which impinge significantly on the agricultural systems, water resources, bio‐ diversity, human health, etc. In spite of inadequate data, few researches have been carried out on rainfall and temperature pattern. Analysis (Shrestha et al, 1999, 2010, Shrestha and Aryal, 2010, Shrestha KL, 2003, etc.) suggests changes in precipitation and temperature pattern. The change is time and space dependent. Changing pattern of temperature is more visible and clear than precipitation.
Changes in evaporation rates, annual river discharge amounts, seasonal and temporal offsets of hydrological patterns, extreme precipitation events, and increased glacial melt are the most pertinent climate change effects that will impact hydroelectric generation. These impacts all affect each other and cannot solely be viewed in isolation. Some of these changes will cause an increase of hydropower generation, while others have the potential to decrease generation. A hydropower facility requires a relatively reliable water source to generate electricity. The uncertainty inherent to modelling future trends make it very difficult to determine the precise effect on climate change that will have on hydroelectric production. However, even with this uncertainty, Nepal still need to plan for future energy demands.
Some useful initiation on assessing the trends in river flows added by global and local changes in climates is carried out for Nepal. There is virtually neither positive trend ie increasing trend nor decreasing trend in Koshi river flows. But there is significant difference in annual mean to the long‐term mean annual flows. Koshi flows found appreciable increased after 1998/99 and in some years difference reaches to 30 percent increased. Tributaries flows also have similar nature but amount deviation and trend is different. Flow deviated from long term mean by 50 percent about in Tamur river. The variability in stream flows of two other basins, Karnali, Narayani river basin also do not differ significantly. In case of Narayani river basin, difference fall below 10 percent in most of the year were as some wet years show about 20 percent. It has been observed that monthly mean fluctuation is noticeable in other snow fed rivers’ hydrograph. The reason could be both changes in watershed morphology and global warming.
There is about 8.46 % contribution to annual flow from snow and glacier melt, a maximum monthly contribution of 22.52 % in May and a minimum monthly contribution of 1.86% in January in Koshi River in Nepal (WWF 2009). An assessment indicated that the snow melt contribution could reach up to 40 %. The worst scenarios as per the present projection are that future flow characteristics of snow fed rivers could appear to be like that of present pattern of non‐snow fed rivers (Bhusal Jk & Sagar P, 2011).
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Nepal has to make large investments to increase the hydro electricity. So a developer will have to carefully consider how climate change will impact hydropower production to determine what role, if any, hydropower should play in their energy futures.
Changes in future electric production depend not only on the type and severity of climate alterations, but also on the facility’s structural characteristics. Vulnerabilities to climate change depend on variety of types and scales of hydropower facilities. While large‐scale reservoir dams are able to regulate flow, produce electricity as desired. Reservoir size is important to evaporation as well, as smaller reservoirs will be more at risk to losing greater proportions of their volume. Therefore, decision‐makers can acquire a basic understanding of how climate change may impact certain areas, and which types of hydropower facilities are least vulnerable to said effects. Similiarly, hyrdro industries will require developing more flexible approaches to managing reservoirs (Soito and Freitas, 2011).
It is imperative to understand how climate change will impact hydroelectric production to meet Nepal’s growing energy demands from hydropower. Hydropower is often developed as a means of generating electricity that reduces emissions that contribute to climate change.
Ben Blackshear et al (2011) created an illustrated framework that shows relative changes in generation capacity due to climate change. Climate change effects are located along the x‐axis and the type and characteristics of hydropower schemes along the y‐axis (Figure 4.2). Discharge, temporal variability, and glacial melt do not apply to pure pumped storage, which is not connected to a river network. Only evaporation is applicable to reservoir surface area to volume ratio (SA:Vol).]
Global warming has been adding severity of glacial melt‐related flood as well as decreasing lean period flows. Although glacial melt water’s proportion of the total flow decreases with greater distance from glaciers due to input from other runoff within the basin, it is important to recognize the contribution of glaciers to downstream flow when considering the impacts of climate change. Climate change has been inducing decreasing trend on freshwater availability not only in Nepal but also in Central, South, East and Southeast Asia, and even in the large river basins.. Regions with distinct seasonal rain cycles and snowmelt seasons typically experience fluctuations in generation due to precipitation’s influence on flow. The seasonality of precipitation causes variability in hydroelectric generation. The other factors determining the responses to climate change impacts on hydropower generation are political, social and economic factors, unique to the region
Though it is difficult to predict the future impacts of climate change, it is certain that climate change will significantly affect ecological qualities of Nepal. Nepal lacks the infrastructure and resources to effectively respond to crises spawned by climate change. So it is recommended to address the water resources sector as a) by studying the impacts of climate variability and Climate Change on river flow regimes and on the ground water table as well as snow covered area in Nepal, b) by identify new flood levels via hydrological and hydraulic modeling, c) by developing the effective measures to manage and
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mitigate water induced disasters like Glofs, cloud burst induced floods etc. and , d) by develop appropriate guidelines for sustainable management of watersheds and water conservation management.
Adaptation and policy recommendation Water Resources Strategy of Government of Nepal (2002) had developed an ambitious action plan to increase hydropower from 527 MW to 22,000 MW (WECS, 2002). The strategy has ignored the river flow variability due to climate changes. But the projection on the depletion of river flows that are likely to be face due to Climate Change, thought not yet reliably quantified, have to be considered for the development hydropower in Nepal. Flow duration curves are affected from temporal variability in precipitation. The nature of snow fed rivers and non‐snow fed rivers have different responses to warming trends. Based on flow patterns, basin responses to monsoon rainfall as well as from the climatic features (WECS/DHMN, 1996), seven hydrological zones are considered as follows.
• Mountain Catchments, • Hills to the north of the Mahabharat Range, rivers rising north of the Siwaliks, the inner Terai, • Pokhara, Nuwakot, Kathmandu, the Sun Koshi tributaries, • Lower Tamur Valley, • River draining the Mahabharat Range, • Kankai Mai Basin; and • Rivers draining from the Churia Range to the Terai
The permanent snowline of the Himalayan region lies close to the 5000 meter elevation. Table 12 presents the areas of major river basins lying in between 5000 m and 5500 m elevation at 100 m intervals (WECS, 2002). The data presented in the table shows that about 23 % of the basin areas of the Himalayan watersheds (excluding the Terai) lies above 5000 m elevation.
Table 11.1: Temperature Sensitive Glaciated Areas of the Major River Basins inNepal.
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Considering the average environmental lapse rate of 6.5o C /km, almost 20 % of the glaciated area above 5000 m is likely to be snow and glacier free area at an increase of air temperature by 1o C. Two degree centigrade rise in temperature can lead a loss of almost 40 % of the area. Similarly, 3o C and 4o C rise in temperature can result in the loss of 58 % and 70 % of snow and glacier areas respectively. Such changes in glacier areas are likely to contribute to the development of glacier lakes increasing potential GLOF hazards. Erosion and sediment transport pattern of sediment is directly influenced by the pattern of changes in precipitation and runoff.
The following activities can be promoted as adaptive measures for the understanding of water resources system and sustainable development of Hydropower.
• Import technology from abroad research and modify, if necessary to suit to Nepal. Hydropower sector are directly linked with hydrology. Therefore, generic adaptive measures, which have been studied and tested in different parts of the world (a few of them are cited in the report), can be considered for Nepal as well. But due to unique physiographic conditions of the Himalayan region of Nepal, several additional adaptive measures must also be considered for better effectiveness in impact reduction. Some rivers are seasonal with little flow during the dry season which renders them unsuitable for year‐round irrigation or hydropower generation without surface storage.
• Collaboration between DHM and hydro companies be established and maintained. Established (if not), maintain and monitor the hydromet networks that represent the basin of interest.
• Promotion of research on case studies in different geographical regions and hydrological zones within the Country. Collaboration of hydro companies with research institutes (TU, KU etc) be promoted and facilitated.
• Encourage storage projects. Wherever possible, provide provision for storages facilities to the existing and under development (under construction)
• Frequent increase in soil erosion, landslide events and debris torrents are major threats in Nepal and such events are likely to increase by Climate Change. So watershed conservation activities be increased, due consideration be given to river morphology during planning, designing and operation phases.
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