Examining the coupled effects of land use and climate change ver 1


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Examining the coupled effects of land use and climate change ver 1

  1. 1. Examining the coupled effects of land use and climate change on watershed functions: experiences from Asia and Africa<br />John M. Gathenya <br />Xing Ma <br />Jianchu Xu <br />Meine van Noordwijk<br />
  2. 2. Flow at watershed outlet is determined by multiple factors<br />Land cover / vegetation<br />Land management<br />Soils and Geology<br />Rainfall <br />Climate / Weather<br />Topography<br />Drainage pattern<br />Watershed shape<br />
  3. 3. <ul><li>Climate change Land use change</li></ul>Less reliable rainfall<br />Longer dry spells<br />More ‘extreme events’<br />Increased drainage<br />Soil compaction<br />Less macropores<br />More demand and less supply of ‘buffer functions’ in our watersheds; increasing buffer capacity will reduce vulnerability and enhance adaptation<br />
  4. 4. Watershedfunctions<br />Site cha- racteristics<br />Relevant<br />for<br />1. Transmit water<br />2. Buffer peak rain events<br />3. Release gradually<br />4. Maintain quality<br />5. Reduce mass wasting<br /><ul><li>Rainfall
  5. 5. Land form
  6. 6. Soil type
  7. 7. Rooting depth (natural vegetation)
  8. 8. Downstream water users,
  9. 9. esp. living in floodplains & river beds,
  10. 10. esp. without storage
  11. 11. or purification
  12. 12. at foot of slope</li></li></ul><li>Definitions<br />Buffering capacity of a watershed is its ability to reduce variation in streamflow relative to rainfall<br />Flow persistence is the fraction of flow on the previous day that can be expected as minimum volume of river flow on a given day<br />
  13. 13.
  14. 14. Role of RHA tools<br />Builds on the concept of PRA but incorporates the use of computer-based hydrological models to:<br />Find how severe problems are and their relationship to land use<br />Find specific land use practices that can reduce the problem <br />Establish the potential for RES to support beneficial land uses<br />Compare LEK and MEK<br />Model scenarios of land use <br />
  15. 15.
  16. 16. GenRiver model<br />Generic river flow model.<br />Distributed process-based model <br />spatial scale: 1-10km2, temporal scale: daily<br />Is a patch level representation of daily water balance.<br />From each patch, the flows are routed to the outlet.<br />Can be used to study the relationship between land use/management and flows.<br />
  17. 17. FlowPer model<br />Models, even simple ones like Genriver are over-parameterized<br />FlowPer can serve two functions: <br />(1) summarize the key parameters that downstream stakeholders can observe on the flow pattern,<br />(2) serve as a parsimonious (parameter-sparse)“null model” <br />Extract as much information about upstream conditions from the flow data <br />
  18. 18. FlowPer model<br />Qt+1 = fp Qt + Qadd<br />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<br />∑Qaddi = (1-fp) ∑Q<br />Ideally buffered: fp=1, Qadd = 0<br />Poorly buffered, erratic: fp=0<br />Can fp be used to indicate watershed quality?<br />
  19. 19. Case Study: Jangkok sub-watershed, Lombok, Indonesia<br />
  20. 20. Gura river<br />4AD01 is 441.9 km2.<br />Rainfall and flow data 6 years 1970-1975 <br />Mean monthly ET values <br />FAO Land cover<br />SOTER Soils database version 1<br />
  21. 21. Genriver / FlowPer results - Gura river <br />Simulated and observed flows at 4AD01<br />Flow hydrographs from GenRiver model<br />Flow persistence from FlowPer model<br />
  22. 22. GuraFlowPer results<br />High quality flow data required for application of FlowPer<br />
  23. 23. GenRiver application in Mara River basin <br />Amala and Nyangores<br />Satellite image analysis showed forest in MRB has declined by almost 60% over the 25 years between 1975 and 1999<br />
  24. 24. Mara river basin<br />Using Genriver, two scenarios were tested in Amala and Nyangores: 1. base case 2. complete forest cover<br />Result: Restoring forest cover may not necessarily increase water yield<br />
  25. 25. SWAT and FlowPer application Nyando basin, W Kenya<br />3587 km2<br />Rain: 800-1600<br />30 yrs records<br />Mean ET from Kericho and Kisumu met <br />Flow simulated with SWAT model<br />
  26. 26. 18 Scenarios<br />
  27. 27. Flow persistence, base case<br />For Nyando basin, the inter-annual variability in rainfall causes a lot of variability in flow persistence <br />
  28. 28. Flow persistence for changed rainfall and land use conditions – R. Nyando<br />
  29. 29. Mean flow and Flood frequency River Nyando<br />Climate change, land surface infiltration and mean flow <br />Land use impact on flood frequency<br />+10% rain, land use and flood frequency<br />
  30. 30. Flow persistence under changing rainfall<br />Flow persistence increases with rainfall<br />Flow persistence higher for improved surface infiltration<br />When surface infiltration is low, of flow persistence does not seem to respond to change in rainfall <br />
  31. 31. GenRiver for Kapingazi river catchment<br />On the southern slopes of Mount Kenya, Area 61 km2<br />Is in Upper Tana River Basin<br />Average annual Rainfall ranges between 1200 mm and 1800mm<br />Rainfall data 1976-1994, some limited flow data for the same period, water permit records.<br />Mean monthly ET for Embu KARI station<br />SOTER soil DB, digital DEM, satellite derived land cover<br />
  32. 32. Kapingazi ...in good times<br />Supplies Embu town with a portion of the water consumed and a number of community and individual irrigation and domestic water projects<br />History of drying up 1984, 2000, 2011<br />Decreased flows attributed to decreased rainfall, increased water demand, planting of eucalyptus, poor water allocation, farming on river banks and illegal extractions<br />
  33. 33. Kapingazicacthment<br />
  34. 34. Rainfall at Embu town and Irangi Forest<br />No discernible trend in mean annual rainfall totals 1978-2008<br />
  35. 35. Farmers say that the rainfall patterns are changing<br />1st rain season totals decreasing, 2nd rain season totals increasing, annual means remaining constant<br />
  36. 36. Genriver model results – Kapingazi hydrograph 1976-1994<br />45 flow measurements spread over the period were used to guide the calibration, some points fit, others do not<br />
  37. 37.
  38. 38. In some extreme dry years, e.g. 1984, actual abstractions exceed low flows at outlet. <br />This explains why the flow in Mar/April 2011 also reached zero<br />
  39. 39. Kejie Watershed<br />The Kejie watershed occupies a total area of 1755 km2<br />The watershed provides ES to Baoshan Prefecture in Yunnan and to Myanmar and Thailand downstream<br />Land use classes: forest, grassland, cropland, settlement, barren and water<br />
  40. 40. Kejie watershed<br />
  41. 41. Kejie watershed<br />Elevation oranges from 963 to 3076 m. <br />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<br />
  42. 42. Kejie watershed Scenarios<br />Temperature: T+1, T+2, T+3, T+4<br />Rainfall: P-10, P-5, P+5, P+10<br />Land cover: forest+, grassland+, crop+, urban+<br />
  43. 43. Land use change and water balance<br />
  44. 44. Climate change and Q and ET<br />
  45. 45. Land use change and Water balance<br />
  46. 46. Land use change and climate change<br />
  47. 47. Conclusions<br />GenRiver a good hydrological model for rapid assessment of small watersheds for PES <br />
  48. 48. Conclusions<br />Impacts of climate change on watershed functions interact with those of land use change: They may reinforce or weaken each other.<br />Both should be considered together in order to identify interactions <br /> 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<br />
  49. 49. Reference<br /><ul><li>van Noordwijk M, Widodo RH, Farida A, Suyamto DA, Lusiana B, Tanika L and Khasanah N. 2011. GenRiver and FlowPer: Generic River Flow Persistence Models. User Manual Version 2.0. . Bogor. World Agroforestry Centre - ICRAF, SEA Regional Office. 119 p.
  50. 50. http://www.worldagroforestry.org/sea/publication?do=view_pub_detail&pub_no= MN0048-11</li></li></ul><li>A frog likes water...but not when it is boiling<br />