UCL DEPARTMENT OF GEOGRAPHY

Climate change impacts on the Mekong River

Daniel Kingston, Richard Taylor, Julian Thompson, Martin ToddDepartment of Geography, University College London

Geoff KiteHydro-Logic Solutions

The Mekong basin

• 795,000 km2

• 4200km long• From Tibetan plateau (>5000m) to

Vietnam and South China Sea• China, Burma, Thailand, Laos,

Cambodia & Vietnam• ~ 50 million people• Socio-economic importance:

– Fish:• 700,000 tons, 300 species p.a. (1992)• Fish are 50-80% total protein intake

– Agriculture– Hydropower

Climatology

• Mid-May to early October: southwesterly circulation, rainy.– 90% annual precip between

May-Oct• October-March: northeasterly

circulation, dry• Snow storage and release in

Tibet vs monsoon rains in lower basin

• Mean annual rainfall ranges from 1000mm in northeast Thailand to >3200mm in mountainous regions of Laos. Mean annual precip (mm)

(IWMI Atlas)

Hydrology

• Mean total annual discharge = 475bn m3

– 6th largest in world

Mekong Basin Streamflow

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Stre

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Mekong at Pakse, 1981-1990 Mekong at Chiang Sen, 1960-1987Mekong at Mukdahan, 1924-1987 Chi at Yasothon, 1953-1987Mun at Ubon Rachathani, 1955-1987

Mun at Ubon

Mekong at Mukdahan

Mekong at Chiang Saen

Mekong at Pakxe

Chi at Yasothon

Hydrological model

• SLURP (Semi-distributed Land-Use Runoff Process) model (Kite, 1995)– Semi-distributed, physically

based• Previously applied to the

Mekong– Kite, G. (2001) Journal of

Hydrology, 253 pp1-13.– Model period 1994-1998

Fast Storage

Runoff

Interflow

Snow Storage

Slow Storage

Infiltration

Percolation

Sublimation

Interception

Snowmelt

Precipitation

Groundwater-flow

Evapo-transpi-ration

Canopy Storage

Transpi-ration

Irrig-ation

Withdrawals

Initial model set-up

• 13 sub-basins derived from DEM– USGS GTOPO-30

• Sub-basins further divided, based on land-use (9 categories)– USGS data

• FAO world soil map

Re-calibration of SLURP for QUEST-GSI

• Change from sparse network of daily station climate data to 0.5 degree gridded monthly data set

• Change of calibration period from 1994-1998 to QUEST 1961-90 baseline period– With 1991-1998 used for model

validation

• Modelled to Pakxe only– 570,000km3, ~70% of basin

Lancang

Mekong1

Namou

Chi

Chi-mun

Nam-ngum

Mekong2Mun

Re-calibration (2)

• Substitution of CRU TS 3 precipitation data with University of Delaware data set

• Change of PET algorithm– From Penman-Monteith to Linacre

method• Data reliability issues

• Manual parameter adjustment

• Final calibration– Nash-Sutcliffe = 0.94– Spearman coefficient = 0.95

• 1991-1998 validation– Consistent with calibration period

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Scenarios

• 1-6 °C prescribed warming on HadCM3• 2 °C prescribed warming on all 7 GCMs

– (HadCM3, HadGEM1, CCCMA, CSIRO, IPSL, MPI, NCAR)

• All 4 SRES scenarios on HadCM3 (2040-69)– A1b, A2, B1, B2

• SRES A1b on all 7 GCMs (2040-69)

Prescribed warming on HadCM3

• Near-linear trend in annual runoff with increased mean global temperature

• Decreased peak season runoff• Increased early season runoff

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baseline1deg2deg3deg4deg5deg6deg

Annual runoff anomaly from baseline

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Prescribed warming on HadCM3:temperature vs precipitation

• Temperature: decreasing peak season flow

• Precipitation: increasing flow from May-December

Precipitation climate change signal

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baseline1deg2deg3deg4deg5deg6deg

Temperature climate change signal

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2deg prescribed warming on all GCMs

• No consistent signal• Either on an annual or

seasonal basis• No outlier GCM

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Annual runoff anomaly from baseline

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hadcm3 cccma csiro ipsl mpi ncar hadgem

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2 degree prescribed warming:temperature vs precipitation

• Temperature climate change signal very similar between GCMs

• Little consistency in precipitation climate change signal between GCMs

Temperature climate change signal

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Precipitation climate change signal

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SRES scenarios on HadCM3 (2040-69)

• Little difference between A1b, A2, B1 and B2

• All show very small (<1%) changes in mean annual runoff

• Decreased peak season flow; slight increase in early season flow

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Annual runoff anomaly from baseline

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SRES A1b on all 7 GCMs (2040-69)• Follows pattern at 2 °C

prescribed warming:• No consistent signal• Either on an annual or

seasonal basis• No outlier GCM

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annual runoff anomaly from baseline

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Summary:Uncertainty envelopes

1-6 °C prescribed warming on HadCM3

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2 °C prescribed warming across all 7 GCMs

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HadCM3 SRES scenarios (2040-2069)

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SRES A1b across all 7 GCMs (2040-69)

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Solid line=baseline; dotted lines indicate upper and lower bounds of climate change signal

Summary

• GCM uncertainty > climate sensitivity and emissions uncertainty

• Common themes– Emissions uncertainty relatively small for 2040-69– Uncertainty from GCMs primarily from precipitation, not

temperature– Little change in low flow season

Further work

• Model uncertainty– Parameterisation– Model structure

• (comparison with global model)

• Land use change• Abstractions

– ?

GLOBAL MODEL

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CATCHMENT MODEL

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SRES A1b (2040-2069)