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)

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 nn

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

The ASB Matrix TP Tomich

ASB Matrix for the Forest Margins of Sumatra

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

Tropical Forest Biomes

River Basins Containing Tropical Forest Biomes

Population density within the pan-tropic basins

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.

Table 1. Measurability of land use impacts by basin size (Kiersch and Tognetti, 2002) x = Measurable impact; – = No measurable impact ___________________________________________________ Impact Type Basin size [km 2 ] _____________________________________________________________________________________ Thermal regimex x ––––– Pathogens xxx–––– Average flow x x x x ––– Peak flowx x x x––– Base flowx 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 xxx x xx 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?

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

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

Precipitation = P Evapotranspiration = E River flow = Q Q quick Q slow E veg E soil E interc E irr infiltration interception E soil + E veg E interc Q slow Q quick Energy- limited E potential Signal modification along river precipitation Looking at the water balance in summary terms: and understanding it from a summation of ‘event’-level processes: We need ‘models’ to keep track of the various interaction terms….

Hydrological null-model

Time Space (km 2 ) HoursDaysWeeksMonths Years ,000 10, ,000 Nested, Overlapping Hydrologic Model Capabilities GENRIVER, DHSVM WANULCAS VIC WBM FALLOW

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

Mae Chaem

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

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

Way Besai Rain and Riverflow exceedance for two types of rain

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

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

B W Progressive land use change 1010 Forest baseline Environmental service functions

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) “Geospatially-explicit process-based models provide fundamental new insight”

Crops (7/9/99) Veg89 (7/9/99) ET SM Veg2000irr N95N96N97N98N99N00 Crop Crop Bad Soil Mae Chaem: SCENARIOS OF HYDROLOGIC RESPONSES

Mun Yanothon Rasi Salai Ubon Ban Chot

Yasothon Rasi Salai Ban Chot Ubon MUN RIVER Scenarios ModelNo Forest All Forest Obs

Mun MEKONG: “Daily/10 km Resolution” Chiang Saen Stung Treng

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

N/A Scenario 1

N/A

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.