1. Trade-offs among Ecosystem Services and Food Security in the Lake Victoria Basin B. Swallow, J. Sang, M. Nyabenge, T. Yatich World Agroforestry Centre (ICRAF), Nairobi, Kenya D. Bundotich, Kenya Ministry of Agriculture, A. Duraiappah, and M. Yashiro, United Nations Environment Programme (UNEP), Nairobi, Kenya

2. Lake Victoria’s Degrading Ecosystems  Sediment and nutrient loading of the lake  Water hyacinth & elephant grass in lake  Declining lake level  A ‘hotspot’ of hunger and poverty

3. The Nyando and Yala basins of Kenya  Both about 3500 km 2  High poverty rates  Dense populations  Flooding in lower areas  Deforestation in upper areas  High rates of HIV / AIDS  Declining agriculture through 1990s  Both contrasting land tenure / settlement types

4. Assessing Trends, Spatial Patterns and Tradeoffs in Ecosystem Services  Using the Millenium Ecosystem Assessment approach, particularly the southern Africa sub-global assessment  Water yield and sediment yield as key regulatory services  Food and non-food agricultural production as key production services  1996, 2000 and 2005  Spatial disaggregation to the smallest possible unit

5. Combining Methods and Data Methods: GIS and Remote sensing Visits to agricultural offices and product buying centres Hydrological modelling using Soil and Water Assessment Tool (SWAT) Data: Secondary GIS data layers Field data on erosion associated with different land uses Aster imagery Wall to wall aerial photos taken in 1996, 2002 and 2005 Daily rainfall and streamflow since 1960s Digital elevation model Agricultural prices, yields and production

6. Value of agricultural production: Nyando

7. Value of agricultural production: Yala

8. Water and sediment yield: Nyando

9. Water and sediment yield: Yala

10. Value / Sediment Yield Tradeoffs: Nyando

11. Value / Sediment Yield Tradeoffs: Yala

12. Conclusions  After general decline in the 1990s, there has been a rebound in agricultural production, largely due to changes in irrigation and agricultural policy.  Food crops – esp maize and sorghum – are generating higher and more dispersed revenue than the ‘cash crops’, esp sugar cane  Tradeoffs between value and sediment yield are highly variable in space and time – implying vulnerability to climate change.  Areas with highest value of production are also areas most affected by inter-ethnic conflict over land.  Sediment yield is highly sensitive to inter-annual variation in rainfall.