Tropical forests and water flows: from small watersheds to the pantropics

1. Tropical forests and water flows: from small watersheds to the pantropics “Functional Value of Biodiversity” Project with support from World Bank Netherlands Partnership Program “FVOB” is a component of ASB’s crosscutting assessment “Forest and Agroecosystem Tradeoffs in the Humid Tropics” a sub-global component of the Millennium Ecosystem Assessment (MA)

2. Team members • Jeffrey Richey, UW • Ellen Douglas & Charles Vörösmarty, UNH • Kate Sebastian & Stanley Wood, IFPRI • Kenneth Chomitz, DECRG • Meine van Noordwijk & Thomas Tomich, ICRAF • plus other team members not here today • plus contributions of others not directly involved in this project n n

3. Overview • Introduction • Integrated assessment of real concerns • Framework • Micro scale • Meso scale • Pantropic scale • Conclusions

4. The ASB Matrix TP Tomich

5. ASB Matrix for the Forest Margins of Sumatra TP Tomich

6. Strong coincidence of watershed functions, biodiversity and poverty alleviation agendas Biodiversity Biodiversity Or Peo-ple Peo-ple Watershed functions Watershed functions Little overlap, separate attention for watershed_functions*poverty and biodiversity* poverty

7. Tropical Forest Biomes

8. River Basins Containing Tropical Forest Biomes

9. Population density within the pan-tropic basins

10. Share of pre-industrial land cover converted by 1992/93 (Contemporary) Conversion is the sum of agricultural (cropland and pasture – rainfed & irrigated) and urban land cover contained in the contemporary land cover.

11. Table 1. Measurability of land use impacts by basin size (Kiersch and Tognetti, 2002) x = Measurable impact; – = No measurable impact • ___________________________________________________ • Impact Type Basin size [km2] • 0.1 1 10 102 103 104 105 • _____________________________________________________________________________________ • Thermal regime x x – – – – – • Pathogens x x x – – – – • Average flow x x x x – – – • Peak flow x x x x – – – • Base flow x x x x – – – • Groundwater • recharge x x x x – – – • Organic matter x x x x – – – • Sediment load x x x x – – – • Nutrients x x x x x – – • Salinity x x x x x x x • Pesticides x x x x x x x • Heavy metals x x x x x x x 1.Is there simply a lack of data here? 2. Are LU impacts on this group of functions really restricted to ‘small’ areas? 3. Do we understand why this could be so? 4. What does it mean for upland-lowland interactions?

12. Watershedfunctions Site cha- racteristics Relevant for • Rainfall • Land form • Soil type • Rooting depth (natural vegetation) 1. Transmit water 2. Buffer peak rain events 3. Release gradually 4. Maintain quality 5. Reduce mass wasting • Downstream water users, • esp. living in floodplains & river beds, • w.o. storage • or purification

13. What matters most in a ‘forest’: cloud interception surface run-on Stream: surface run-off sub-surfacelateral inflow rainfall canopy water evaporation Forest transpiration surface evaporation the trees through-fall the landscape stem-flow { infiltration the soil quick- flow recharge ? lateral outflow uptake base flow percolation

14. Looking at the water balance in summary terms: Precipitation = P River flow = Q Evapotranspiration = E Eveg Esoil Eirr Einterc Qquick Qslow precipitation Signal modification along river Einterc Energy-limited Epotential interception Qquick Esoil + Eveg infiltration Qslow and understanding it from a summation of ‘event’-level processes: We need ‘models’ to keep track of the various interaction terms….

15. Hydrological null-model

16. Nested, Overlapping Hydrologic Model Capabilities Space (km2) 100,000 WBM 10,000 VIC 1,000 FALLOW GENRIVER, DHSVM WANULCAS 100 10 1 Time Years Hours Days Weeks Months

17. River flow Rainfall Way Besai (Indonesia), 2.5 m rainfall, 100 persons km-2 Mae Chaem (Thailand), 1.5 m rainfall, 10 persons km-2

18. Mae Chaem

19. Basic properties: transforming rainfall signal to stream and riverflow signals Exceedance probability Area under the curve: Rainfall = ET + River + +storage 0 rainfall stream river Importance declines with time of consideration 1 mm day-1

20. Points indicating ‘breakdown’ of nor-mal buffering at extreme events Sorted river flow, mm/day Slope ~ 1 – buffering indicator River flow on rainless days Sorted rainfall, mm/day

21. Way Besai Rain and Riverflow exceedance for two types of rain

22. Period 1 2 3 Measurement point Plot-level buffering gets lost…. But the internal floodplain replaces its role Tentative interpretation…..

23. Macropore distribution 1.5 m Coffee 1 yr Forest Coffee 3 yr Coffee 10 yr Coffee 7 yr

24. Forest baseline 1 0 W 1 2 Environmental service functions B 4 3 Progressive land use change

25. “Geospatially-explicit process-based models provide fundamental new insight” MEKONG VIC (Variable Infiltration Capacity) Meso/Macroscale Landscape/Hydrologic Model (Daily, 1-10 km) MAE CHAEM DHSVM (Distributed Hydrology Soil Vegetation Model) Micro/Mesoscale Landscape/Hydrologic Model (4h, 150m)

26. Crop Crop Bad Soil Mae Chaem: SCENARIOS OF HYDROLOGIC RESPONSES Veg89 (7/9/99) Crops (7/9/99) 1500 Veg2000irr ET 1000 500 SM 0 N95 N96 N97 N98 N99 N00

27. Ban Chot Yanothon Rasi Salai Ubon Mun

28. 90 90 90 90 95 95 95 95 00 00 00 00 80 80 80 80 85 85 85 85 MUN RIVER Scenarios All Forest Obs Model No Forest 1500 5000 Ban Chot Yasothon 4000 1200 900 3000 2000 600 300 1000 0 0 5000 10000 Ubon Rasi Salai 4000 8000 3000 6000 2000 4000 1000 2000 0 0

29. 15000 Chiang Saen 12000 9000 6000 3000 0 60000 Stung Treng 45000 30000 15000 Mun 0 90 90 95 95 00 00 80 80 85 85 MEKONG: “Daily/10 km Resolution”

30. Lateral Transport Precipitation Discharge Hydrographs Evapo- transpiration Channel Topology WBM/WTM Runoff

32. Scenario 1 N/A

33. N/A

35. Tropical forests and water flows • Deforestation increases total water supply. • Reforestation does not cause dry rivers to flow again. • Upland deforestation increases risks of lowland flooding (1-20 year return period). • Upland deforestation is a small factor in the most devastating floods. • Forest degradation produces many possible trajectories of change in biodiversity and watershed function – these policy objectives are not tightly linked and there are a wide range of options.