Impacts of Hydrology and Habitat Changes on the Primary Production of the Tonle Sap, Southeast Asia’s Largest Lake.


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Arias, M.E., Cochrane, T.A., Piman, T. and Kummu M. (2012) Impacts of hydrology and habitat changes on the primary production of Southeast Asia's largest lake. IWA (International Water Association) World Congress on Water, Climate and Energy. Dublin, Ireland, 13-18 May 2012.

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  • Graphs plotted from LMB model resultsCC from 1 simulation of A1b. Different simulations have a good range of results, and even more among CC scenarios
  • July is not shown or used in the estimates because the model resets the sedimentation every year on that month. Sediment concentration is assumed to change according to flow, but changes in suspended sediment caused by dam trapping are not considered yet
  • Impacts of Hydrology and Habitat Changes on the Primary Production of the Tonle Sap, Southeast Asia’s Largest Lake.

    1. 1. Impacts of Hydrology and Habitat Changes on the Primary Production of the Tonle Sap, Southeast Asia’s Largest Lake Mauricio E. Arias*, Tom A. Cochrane, Thanapon Piman, and Matti Kummu
    2. 2. The Mekong: context & challenges• River length: 4,800 km• Basin area: 795,000 km2• Relevance – livelihoods/ecosystems adapted to hydrological cycle – biodiversity• Mekong challenges – Hydropower – Irrigation – Climate change
    3. 3. Tonle Sap: the Great Lake of Cambodia• 2,600-15,000 km2• Largest natural flow reversal system in the world• Core of one of the largest inland fisheries in the world• Fish is the main protein source in Cambodia• Important habitat for migratory fish• Tonle Sap flood pulse changing with hydropower and climate in the Mekong
    4. 4. Research Overview• Broader project: My contribution: Community patterns• Goal: Modelling and monitoring impacts from large-scale disruptions to the Mekong’s How do changes Landscape in hydrology Production patterns impact the Tonle hydrology Sap habitats? 1. hydrology/hydropower operation modelling 2. Downstream hydrological Water quality and ecological impacts
    5. 5. Modelling OverviewMain question: how do changes in hydrology impact the Tonle Sap habitats? Landscape patterns Primary production Link aquatic primary production to Link habitat cover to flooding Approach hydrodynamics and habitat cover and and project future changes project future changes Tools GIS modelling Dynamic modelling Hydrological models and Hydrological models, habitat cover, Data sources monitoring, elevation surveys field surveys
    6. 6. Production and landscape modelling procedures
    7. 7. Floodplain HabitatsHabitat code Gallery Forest (GF) Open Water (OW) Rainfed habitats (RF) 0 15 30 60 Seasonally flooded habitats (SF) Kms Transitional habitats (T)
    8. 8. Water level changes : shifting the balance? Average year 10•Large seasonal fluctuation•Large inter-annual range 9•Levels during dry season getting higher 8 Dry year 10•Levels during wet season getting lower 7 observed driest (1998) 9 Development 6 Climate changemasl 8 Climate change + hydropower 5 7 observed average (1997) 4 Hydropower 6 masl 3 Climate change 5 Climate change + hydropower 2 4 1 3 May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr 2 1 May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr
    9. 9. Habitat Cover Changes ClimateClimate change change +Hydropower Hydropower shift2030a1rv SHIFT CODE shift2030a1bHabitat code SHIFT CODE GF to OW SHIFT CODE Habitat code to GF Gallery Forest (GF) SF to OW GF GF to OW Open Water (OW) Gallery Forest (GF) SF to T GF SF to RF to OW Rainfed habitats (RF) Open Water (OW) TS to RF SF to GF SF to T Seasonally flooded habitats (SF) 0 3 6 12 0 2.5 5 0 2.5 5 0 2.5 5 10 10 10 Rainfed habitats (RF) Kms Kms 0 15 30 Kms 60 Kms Transitional habitats (T) T to SF T T to to SF RF Seasonally flooded habitats (SF) Kms Transitional habitats (T) Baseline map Changes from baseline
    10. 10. Changes in sedimentation 1.2 Total annual change Climate change Hydropower Climate change + hydropowerAverage of monthly net sedimentation, 0.8 -13% to -35% -38% - 36% to -51% Baseline (1987-2005) million tons 0.4 Climate change g/m2 % change 900 800 700 600 Hydropower 80 60 500 40 20 400 300 200 Climate change + hydropower 0 -20 0.0 100 0 -40 -60 -80 -100 Baseline average year Changes by hydropower -0.4 AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN
    11. 11. Changes in Aquatic Primary Production Total annual change Climate Hydropower Climate 1.3 change change + hydropowerAverage of monthly primary production, 1.1 -13% to - - 25% to - -27 % 0.9 21% 36% million tonsC/day 0.7 0.5 Baseline (1987-2005) Climate change 0.3 Hydropower Climate change + hydropower 0.1 MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR
    12. 12. Summary of Results Primary Water levels Habitat cover Sedimentation Production Open water (+35%) Dry season (+0.8m)Hydropower Gallery forest (-23%) -38% -27% Wet season (-0.5m) Rainfed (+15%) Open water (+21%) Climate Dry season (≈0m) Gallery forest (-80%) -13 to -35% -13 to -21% change Wet season (-0.2m) Climate Open water (+38%) Dry season (+0.8m) change + Gallery forest (-31) -36 to -51% -25 to -36% Wet season (-0.7m)hydropower Rainfed (+11%)
    13. 13. Implications of Results• Habitat cover and ecosystem function will be impacted by changes in the Mekong hydrology• Ecosystem and livelihoods will have to adapt to new conditions• Strong pressures on natural resources and lack of livelihood diversification are challenges to adaptation.• primary production ≈ food
    14. 14. Acknowledgments