ESTIMATION OF THE CLIMATE VARIABILITY IMPACT ON WATER RESOURCES IN THE NYABUGOGO CATCHMENT WITH FOCUS ON THE NYABUGOGO SWAMP

ESTIMATION OF CC AND VARIABILITY IMPACTS AND MITIGATION MEASURES ON WATER RESOURCES IN THE NYABUGOGO SWAMP IN RWANDA

By

Eng. Omar MUNYANEZA, PhDomarmunyaneza1@gmail.com/ +250 788560783

Department of Civil & Environmental EngineeringCST/University of Rwanda

24th March 2016IPAR 5th ANNUAL RESEARCH CONFERENCE

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Presentation outlineIntroductionStudy Area DescriptionObjectivesResearch MethodologyResults and DiscussionsConclusion and Recommendations

IntroductionWater is a finite resource vital for sustaining life on earth;While water is a cross-cutting resource;The entire food production chain depends on water;Water resources support economic growth through, industrial processing, energy, transportation, agriculture and tourism; Water resources are under pressure from population growth and rapid economic development in Rwanda;However, water resources is directly linked to the climate which is highly variable;

Introduction (Contd)The climate variability have a great impact on sustainable WRM in the world;Water resources in the Nyabugogo catchment is seriously affected by the climate variability; Consequently, nowadays the Nyabugogo swamp is being flooded due to the global phenomena and intensive human activities; This increases the danger of sudden flooding of rivers in a catchment.

Example of recent flood case due probably to Climate ChangeThe recent floods occurred in Feb 2013 affected Nyabugogo wetland and caused loss of properties, loss of 4 human lives through a car which was drawn by the water, and Disruption of socio-economic activities, through the business in the area and other issues related to transport facilities.

Loss of 4 human lives through this car

Introduction (End)An integrated and coordinated management approach is needed to provide answers to water resources in the Nyabugogo swamp.

Nyabugogo catchment boundaries

Study Area

Total area of 1,647 km2Nyabugogo river, total length of 42.7 kmMain Inflow is lake Muhazi

RESEARCH OBJECTIVESTo investigate the recent trends and variability of climatic data and streamflow trend in the Nyabugogo catchment, and To propose possible mitigation with the goal of estimating the impact caused by this trend on water resources in the Nyabugogo swamp (220 ha).

Methodology

Trends analysis of data set of daily maximum, minimum temperatures, rainfall and evaporation of Kigali airport station (1981-2012) from Rwanda Meteorology Agency (RMA).And Nyabugogo River Discharge data collected from Rwanda Natural Resources Authority (RNRA).

Methodology (Contd)In this study, the Mann Kendal (MK) non-parametric trend test has been performed using XLSTAT to detect trends;The time series from each parameter was also subjected to the Pettitt Test (Pettitt, 1979) to detect abrupt changes in hydrological series;In addition, SPSS software was used to assess a non-parametric correlation between climate variables.

Methodology (Contd)Trend AnalysisThe test statistics Z is computed as:

A positive (negative) value of Z signifies an upward/ downward) trend.

Correlation between climate variablesThe Kendalls tau_b and Spearman rank test were used to determine the correlation coefficient;It helps us to know the magnitude of the correlation between climatic variables;The Spearman rank test, is a simple measure of correlation between 2 data series and is a special case of the Pearson product-moment coefficient (Myers and Well, 2003).Methodology (End)

Results and discussionsMann-Kendall trends results on temperature

Discussion on temperature trends Results The Kigali Airport station shows a slight decrease, then a significant increase in trend in the period 1987-1994;Though, most of the part of the period 1991-2012 corresponds to a significant increase in To trends; The observed warming was supported by Collins (2011) who demonstrated that significant increasing temperature trends were found on average all over the African continent. Pettitt tests revealed that abrupt change points was observed in the years 1985, 1987,1989, 1993,1998, 2001, 2008 and 2009.

Mann-Kendall trends results for rainfall

Discussions on rainfall trends resultsThe results of the Mann-Kendall for rainfall shows that there is in general a significant decrease in rainfall. Pettitt tests for rainfall revealed that abrupt change points was observed in the years 1981, 1998, 2008 and 2010. Nevertheless, Nyabugogo wetland has been prone to heavy floods and this may be explained by increase in urbanization which results in increase of impermeable areas.

Mann-Kendall trends results for evaporation

Discussions on evaporation trends resultsThe results showed that there is a significant increase trend in evaporation in the Nyabugogo catchment,The increasing temperature results in an increase in potential evaporation largely because water holding capacity of the air is increased,Pettitt tests for evaporation revealed that abrupt change points in the years 1991, 1995, 1998, 2001, 2008 and 2009, 2010.

Mann-Kendall trends results for dischargeThe trend analysis of the mean annual discharge of the Nyabugogo river was performed using Mann-Kendall test statistic;Due to the large data gap discharge data, it was difficult to analyze and draw a conclusion;The % value of missing streamflow data is greater than 50% (1984 to 1994 and 2001 to2009), thus we cannot rely on the results of such a poor data;Long records of runoff are essential to determine whether runoff of a river is changing over time.

Correlation between climate variables

Correlation between climate variablesStreamflow was slightly correlated with the total rainfall;Positive relationship between rainfall and streamflow was observed;The significance test (2-tailed) was performed at 10% and the higher significance was found to be between temperature and rainfall (0.435).In fact, rainfall and temperature are physically related through the dependence of atmospheric moisture on temperature.

Facts impact of climate variability and/or change on water resources in the Nyabugogo swamp

Facts impact of climate variability and/or change on water resources in the Nyabugogo swamp

Facts impact of climate variability and/or change on water resources in the Nyabugogo swamp

Summary of climate variability impact on water resources in the Nyabugogo swamp

ConclusionsA strong correlation between temperature and evaporation was detected; but the correlation between rainfall and discharge was found to be weak;The results showed a significant decrease in rainfall;The analysis of discharge data did not show significant results due to a large gap observed in it.Holistic approach need to be implemented to address the challenges related to climate variability and change by applying integrated methods for a good sustainable water resources management in the Nyabugogo catchment.

RecommendationsMore research on how the severity of storms and other extreme hydrologic events might change is necessary.Increased and widespread hydrologic monitoring systems are neededA regular data record should be given a careful attention for future research by installing enough equipment with continuous data collection in the catchment.There should be a systematic reexamination of engineering design criteria and operating rules of existing dams and reservoirs under conditions of climate change.

Thank you for you Kind attention