routing GenRiver 1.0 Distributed process-based model spatial scale: ha,temporal scale: daily Can be used as a tool to explore our understanding of historical changes in river flow due to land use change

stem-flow through-fall rainfall cloud interception lateral outflow percolation recharge infiltration surface evaporation transpiration canopy water evaporation uptake base flow { surface run-on sub- surface lateral inflow surface run-off Quick flow Trees Soil Hydrological functions of forest: Landscape drainage ?

PES Regulation Spatial planning ‘Permanent’ site characteristics Upland land use Watershed functions Downstream water users & stakeholders Riverbed engineering povert y

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, esp. without storage or purification at foot of slope

GenRiver 1.0 a simple model that translates a plot-level water balance to landscape level river flow Land cover influences: * evapotranspiration -> water yield (immediate) * infiltration (medium term ~ soil type)

3. Subsurface flow into streams: ‘interflow’ or ‘soilquickflow’ 1. Interception & evaporation from wet surfaces 5. Gradual release to streams through deep soil pathways 2. Overland flow into streams: quickflow 4. Uptake by plants for transpiration (+ soil evaporation) Unit hydrograph – what happens to an ‘average’ drop of rainfall?

The core of the model : Patch level represent daily water balance, driven by local rain rainfall and modified by land cover and soil properties of the patch

The patch can contribute to three types of stream flow : 1.Surface quick flow – on the day of rain event 2.Soil quick flow – on the next day after rain event 3.Base flow – via gradual release of groundwater

3. Subsurface flow into streams: ‘interflow’ or ‘soilquickflow’ 1. Interception & evaporation from wet surfaces 5. Gradual release to streams through deep soil pathways 2. Overland flow into streams: quickflow 4. Uptake by plants for transpiration (+ soil evaporation) Unit hydrograph – what happens to an ‘average’ drop of rainfall?

1. Interception & evaporation from wet surfaces 1 Step 1 – canopy interception Rainfall per event, mm Water storage on leaf sur- faces, mm Capacity limited Throughfall probability 1:1 Current LAI Waterfilm thickness Will evaporate within a day =Cap*(1-EXP(-Rain/Cap)) Calder (2004) HYLUC

1. Interception & evaporation from wet surfaces 2. Overland flow into streams: quickflow 1 2 Step 2 – Lack of Infiltration => overland flow Two conditions lead to overland flow: Surface infiltrability less than required during storm (‘Hortonian’ overland flow, ‘sealing’ of the surface’); slope, surface roughness and rainfall intensity determine the time available for infiltration Saturation-limited: surface soil layers are saturated and rate of outflow determines possible rate of inflow Rain duration, Can.Interc.Delay Surface staorage, Slope SoilSat - Actual PotInfRate

3. Subsurface flow into streams: ‘interflow’ or ‘soilquickflow’ 1. Interception & evaporation from wet surfaces 2. Overland flow into streams: quickflow Step 3 – Soil quickflow: drain towards ‘field capacity’ SoilQuickFlow: Max(0,Soil- FieldCap) Saturation GW store Percolation Fraction GW release Fraction Baseflow FC ‘Two-tank model’ RootZone store

3. Subsurface flow into streams: ‘interflow’ or ‘soilquickflow’ 1. Interception & evaporation from wet surfaces 2. Overland flow into streams: quickflow 4. Uptake by plants for transpiration (+ soil evaporation) Step 4 – Plant uptake and transpitation (E pot – IntercEff * E interc ) * W_avail Soil water content FC*DroughtFactor (VegType) PWP Energy driven, e.g.Penman Evaporation of intercepted water reduces transp. demand

3. Subsurface flow into streams: ‘interflow’ or ‘soilquickflow’ 1. Interception & evaporation from wet surfaces 5. Gradual release to streams through deep soil pathways 2. Overland flow into streams: quickflow 4. Uptake by plants for trans- piration (+ soil evaporation) Step 5 – Percolation to streams as ‘slow flow’ Saturation Percolation Fraction GW release Fraction Baseflow GW store RootZone store

3. Subsurface flow into streams: ‘interflow’ or ‘soilquickflow’ 1. Interception & evaporation from wet surfaces 5. Gradual release to streams through deep soil pathways 2. Overland flow into streams: quickflow 4. Uptake by plants for transpiration (+ soil evaporation) Unit hydrograph – what happens to an ‘average’ drop of rainfall?

Topology of stream network: distances to array of observation points Obs point SubA SubB SubC SubD ….. F G D C E B A

Array dimensions in the model

Model implementation in Excel GenRiver.xls : 1.Rain & Debit data (daily) 2.Land cover 3.Subcatchment info

Model implementation in Stella GenRiver.stm Model sector

Model implementation in Stella GenRiver.stm Input section

Model implementation in Stella GenRiver.stm Patch level water balance

Model implementation in Stella GenRiver.stm River flow

Default run of GenRiver 1.0 measuredpredicted

measuredpredicted When seen over a long time series, both under- and over-estimates occur in dry periods, but the model tends to exaggerate peaks

The model is in the ‘right range’ but underestimates flows in dry periods and exaggerates peaks measuredpredicted

Model implementation in Stella GenRiver.stm Output sector

GenRiver application in Sumberjaya - Indonesia Using 2 time series of land cover fractions : Year 3(%) Year 20(%) Forest Cropland Coffee Explore the effect of land cover & spatial pattern for rainfall on river flow

Cumulative water balance

River flow using Pathcy & Homogenous rain Patchy year 3 Patchy year 20 Hm year 3 Hm year 20

SpatRain.xls SpatRain.exe WShedInd.xls GenRiver.stm What we offer Input data Output - hydrographs Criteria & indicators of watershed functions Participants Expectations? Climate, soil, scale, land use

Simulation results: current ‘MixedLU’ situation not much different from ‘forest’, but for a ‘Degraded soil’ buffering would be much less Homogenous rainPatchy rain current Degraded soil current Degraded soil