UCL DEPARTMENT OF GEOGRAPHY Climate change impacts on the Mekong River Daniel Kingston, Richard Taylor, Julian Thompson, Martin Todd Department of Geography, University College London Geoff Kite Hydro-Logic Solutions
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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Month
Stre
amflo
w, m
3/s
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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obsobs-15%obs+15%model
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% exceedence
mea
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(m
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obsmodel
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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1deg 2deg 3deg 4deg 5deg 6deg
anom
aly
(%)
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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j f m a m j j a s o n dmea
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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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baselinehadcm3cccmacsiroipslmpincarhadgem1
Annual runoff anomaly from baseline
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hadcm3 cccma csiro ipsl mpi ncar hadgem
anom
aly
(%)
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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baselinehadcm3cccmacsiroipslmpincarhadgem
Precipitation climate change signal
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baselinehadcm3cccmacsiroipslmpincarhadgem
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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baselinea1ba2b1b2
Annual runoff anomaly from baseline
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a1b a2 b1 b2
anom
aly
(%)
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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baselinehadcm3cccmacsiroipslmpincarhadgem
annual runoff anomaly from baseline
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hadcm3 cccma csiro ipsl mpi ncar hadgem
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Summary:Uncertainty envelopes
1-6 °C prescribed warming on HadCM3
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-3s-1
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2 °C prescribed warming across all 7 GCMs
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(m
-3s-1
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HadCM3 SRES scenarios (2040-2069)
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mea
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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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baselinecccmaipslmpincarhadcm3
CATCHMENT MODEL
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baselinecccmaipslmpincarhadcm3
SRES A1b (2040-2069)