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 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 Mekong at discharge = 475bn m3 Mukdahan –6th largest in world Mekong at Chiang Saen
Mekong Basin Streamflow 30000 25000 Chi at 20000 Yasothon
15000
10000
Streamflow, m3/s 5000
0 123456789101112 Month Mekong at Pakse, 1981-1990 Mekong at Chiang Sen, 1960-1987 Mekong at Mukdahan, 1924-1987 Chi at Yasothon, 1953-1987 Mun at Mun at Ubon Rachathani, 1955-1987 Ubon Mekong at Pakxe Precipitation
Hydrological model Interception Canopy Storage
Sublimation Snow Storage Snowmelt Irrig- ation Evapo- transpi- Runoff ration Fast Storage Infiltration • SLURP (Semi-distributed Interflow Percolation Transpi- Land-Use Runoff Process) ration Slow Storage
model (Kite, 1995) Groundwater- flow
– Semi-distributed, physically Withdrawals based • Previously applied to the Mekong – Kite, G. (2001) Journal of Hydrology, 253 pp1-13. – Model period 1994-1998 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 Lancang degree gridded monthly data set
• Change of calibration period Namou from 1994-1998 to QUEST 1961-90 baseline period Nam- ngum Mekong1 – With 1991-1998 used for model validation Chi
• Modelled to Pakxe only Mun – 570,000km3, ~70% of basin Mekong2 Chi-mun Re-calibration (2) ) -1
s 35000 -3 • Substitution of CRU TS 3 30000 precipitation data with University of 25000 obs Delaware data set 20000 obs-15% 15000 obs+15% 10000 model • Change of PET algorithm 5000 – From Penman-Monteith to Linacre 0 mean daily discharge (m discharge mean daily method 123456789101112 • Data reliability issues
• Manual parameter adjustment 50000 40000 ) -1 30000 obs • Final calibration s -3 20000 model – Nash-Sutcliffe = 0.94 (m – Spearman coefficient = 0.95 10000
mean daily discharge 0 • 1991-1998 validation 0 20406080100 % exceedence – Consistent with calibration period 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
Annual runoff anomaly from baseline
• Near-linear trend in annual 5 runoff with increased mean
global temperature 0 1deg 2deg 3deg 4deg 5deg 6deg • Decreased peak season runoff anomaly (%)
• Increased early season runoff -5
) 30000
25000 baseline 20000 1deg 2deg 15000 3deg 4deg 10000 5deg 5000 6deg
mean daily discharge (cumecs 0 jfmamjjasond Prescribed warming on HadCM3: temperature vs precipitation
Temperature climate change signal -
30000 baseline 25000 • Temperature: decreasing 1deg 20000 ) 2deg -1
peak season flow s 15000 3 3deg 10000 4deg • Precipitation: increasing flow 5000 5deg 0 from May-December 6deg mean daily discharge (m discharge mean daily j fmamj j asond
Precipitation climate change signal -
35000 baseline 30000 25000 1deg ) 2deg -1 20000 s 3 15000 3deg 10000 4deg 5000 5deg 0 6deg mean daily discharge (m discharge mean daily j fmamj j asond 2deg prescribed warming on all GCMs
Annual runoff anomaly from baseline • No consistent signal 10 5
• Either on an annual or 0 hadcm3 cccma csiro ipsl mpi ncar hadgem seasonal basis -5 anomaly (%) -10
• No outlier GCM -15
) 35000 -1 s
-3 30000 baseline hadcm3 25000 cccma 20000 csiro 15000 ipsl mpi 10000 ncar 5000 hadgem1
mean daily discharge (m 0 j fmamj j asond 2 degree prescribed warming: temperature vs precipitation
Temperature climate change signal
e 30000 baseline • Temperature climate change 25000 hadcm3 20000 cccma signal very similar between 15000 csiro
GCMs (m-3s-1) 10000 ipsl 5000 mpi
• Little consistency in mean dailydischarg 0 ncar jfmamjjasond hadgem precipitation climate change signal between GCMs Precipitation climate change signal
35000 baseline 30000 hadcm3 25000 cccma 20000 csiro 15000
(m-3s-1) 10000 ipsl 5000 mpi 0 ncar mean daily discharge discharge mean daily hadgem jfmamjjasond SRES scenarios on HadCM3 (2040-69)
Annual runoff anomaly from baseline
• Little difference between A1b, 5
A2, B1 and B2 3
• All show very small (<1%) 1
changes in mean annual runoff -1 a1b a2 b1 b2 anomaly (%) anomaly • Decreased peak season flow; -3 slight increase in early season -5 flow
) 30000 -1 s -3 25000
20000 baseline a1b 15000 a2 b1 10000 b2 5000
mean daily discharge (m 0 jfmamjjasond SRES A1b on all 7 GCMs (2040-69)
• Follows pattern at 2 °C annual runoff anomaly from baseline prescribed warming: 10 5
• No consistent signal 0 hadcm3 cccma csiro ipsl mpi ncar hadgem -5
• Either on an annual or % anomaly -10 seasonal basis -15 • No outlier GCM
) 30000 -1 s -3 25000 baseline hadcm3 20000 cccma csiro 15000 ipsl 10000 mpi ncar 5000 hadgem
mean daily discharge (m discharge daily mean 0 123456789101112 Summary: Uncertainty envelopes
1-6 °C prescribed warming on HadCM3 2 °C prescribed warming across all 7 GCMs
30000 35000 25000 30000
) 20000 ) 25000 -1 -1
s s 20000
-3 15000 -3 15000 (m 10000 (m 10000 5000 5000 0 0 mean daily discharge discharge mean daily discharge mean daily jfmamjjasond jfmamjjasond
HadCM3 SRES scenarios (2040-2069) SRES A1b across all 7 GCMs (2040-69)
30000 30000 25000 25000
) 20000 ) 20000 -1 -1 s s
-3 15000 -3 15000
(m 10000 (m 10000 5000 5000 0 0 mean daily discharge discharge mean daily discharge mean daily jfmamjjasond jfmamjjasond 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
SRES A1b (2040-2069)
GLOBAL MODEL
200 baseline • Model uncertainty 150 cccma ipsl 100 – Parameterisation mpi
runoff (mm) 50 ncar – Model structure hadcm3 0 • (comparison with JFMAMJJASOND global model) • Land use change CATCHMENT MODEL 200 • Abstractions baseline 150 cccma ipsl –? 100 mpi
runoff (mm) 50 ncar hadcm3 0 JFMAMJJASOND