1. Examining the coupled effects of land use and climate change on watershed functions: experiences from Asia and Africa John M. Gathenya Xing Ma Jianchu Xu Meine van Noordwijk

2. Flow at watershed outlet is determined by multiple factors Land cover / vegetation Land management Soils and Geology Rainfall Climate / Weather Topography Drainage pattern Watershed shape

5. Land form

6. Soil type

7. Rooting depth (natural vegetation)

8. Downstream water users,

9. esp. living in floodplains & river beds,

10. esp. without storage

11. or purification

14. Role of RHA tools Builds on the concept of PRA but incorporates the use of computer-based hydrological models to: Find how severe problems are and their relationship to land use Find specific land use practices that can reduce the problem Establish the potential for RES to support beneficial land uses Compare LEK and MEK Model scenarios of land use

16. GenRiver model Generic river flow model. Distributed process-based model spatial scale: 1-10km2, temporal scale: daily Is a patch level representation of daily water balance. From each patch, the flows are routed to the outlet. Can be used to study the relationship between land use/management and flows.

17. FlowPer model Models, even simple ones like Genriver are over-parameterized FlowPer can serve two functions: (1) summarize the key parameters that downstream stakeholders can observe on the flow pattern, (2) serve as a parsimonious (parameter-sparse)“null model” Extract as much information about upstream conditions from the flow data

18. FlowPer model Qt+1 = fp Qt + Qadd Where Qt and Qt+1 are river flows on subsequent days, fp is flow persistence factor (0<fp<1) and Qadd is a random variate reflecting input from recent rainfall ∑Qaddi = (1-fp) ∑Q Ideally buffered: fp=1, Qadd = 0 Poorly buffered, erratic: fp=0 Can fp be used to indicate watershed quality?

19. Case Study: Jangkok sub-watershed, Lombok, Indonesia

20. Gura river 4AD01 is 441.9 km2. Rainfall and flow data 6 years 1970-1975 Mean monthly ET values FAO Land cover SOTER Soils database version 1

21. Genriver / FlowPer results - Gura river Simulated and observed flows at 4AD01 Flow hydrographs from GenRiver model Flow persistence from FlowPer model

22. GuraFlowPer results High quality flow data required for application of FlowPer

23. GenRiver application in Mara River basin Amala and Nyangores Satellite image analysis showed forest in MRB has declined by almost 60% over the 25 years between 1975 and 1999

24. Mara river basin Using Genriver, two scenarios were tested in Amala and Nyangores: 1. base case 2. complete forest cover Result: Restoring forest cover may not necessarily increase water yield

25. SWAT and FlowPer application Nyando basin, W Kenya 3587 km2 Rain: 800-1600 30 yrs records Mean ET from Kericho and Kisumu met Flow simulated with SWAT model

26. 18 Scenarios

27. Flow persistence, base case For Nyando basin, the inter-annual variability in rainfall causes a lot of variability in flow persistence

28. Flow persistence for changed rainfall and land use conditions – R. Nyando

29. Mean flow and Flood frequency River Nyando Climate change, land surface infiltration and mean flow Land use impact on flood frequency +10% rain, land use and flood frequency

30. Flow persistence under changing rainfall Flow persistence increases with rainfall Flow persistence higher for improved surface infiltration When surface infiltration is low, of flow persistence does not seem to respond to change in rainfall

31. GenRiver for Kapingazi river catchment On the southern slopes of Mount Kenya, Area 61 km2 Is in Upper Tana River Basin Average annual Rainfall ranges between 1200 mm and 1800mm Rainfall data 1976-1994, some limited flow data for the same period, water permit records. Mean monthly ET for Embu KARI station SOTER soil DB, digital DEM, satellite derived land cover

32. Kapingazi ...in good times Supplies Embu town with a portion of the water consumed and a number of community and individual irrigation and domestic water projects History of drying up 1984, 2000, 2011 Decreased flows attributed to decreased rainfall, increased water demand, planting of eucalyptus, poor water allocation, farming on river banks and illegal extractions

33. Kapingazicacthment

34. Rainfall at Embu town and Irangi Forest No discernible trend in mean annual rainfall totals 1978-2008

35. Farmers say that the rainfall patterns are changing 1st rain season totals decreasing, 2nd rain season totals increasing, annual means remaining constant

36. Genriver model results – Kapingazi hydrograph 1976-1994 45 flow measurements spread over the period were used to guide the calibration, some points fit, others do not

38. In some extreme dry years, e.g. 1984, actual abstractions exceed low flows at outlet. This explains why the flow in Mar/April 2011 also reached zero

39. Kejie Watershed The Kejie watershed occupies a total area of 1755 km2 The watershed provides ES to Baoshan Prefecture in Yunnan and to Myanmar and Thailand downstream Land use classes: forest, grassland, cropland, settlement, barren and water

40. Kejie watershed

41. Kejie watershed Elevation oranges from 963 to 3076 m. In the 40 years, dramatic change in land cover, gradual increase in temperature, no trend in mean annual rainfall, change in rainfall for some months

42. Kejie watershed Scenarios Temperature: T+1, T+2, T+3, T+4 Rainfall: P-10, P-5, P+5, P+10 Land cover: forest+, grassland+, crop+, urban+

43. Land use change and water balance

44. Climate change and Q and ET

45. Land use change and Water balance

46. Land use change and climate change

47. Conclusions GenRiver a good hydrological model for rapid assessment of small watersheds for PES

48. Conclusions Impacts of climate change on watershed functions interact with those of land use change: They may reinforce or weaken each other. Both should be considered together in order to identify interactions Single effects of land cover change tend to be greater than single effects of climate change...in some cases, effect of inter-annual variability of rainfall is even greater