This project aims to support farmers and upstream users to curb soil erosion that leads to less water and high cleaning costs.
The Tana-Nairobi Water Fund is a public-private scheme uniting big business, utilities, conservation groups, government, researchers, and farmers. It aims to increase farm productivity upstream while improving the water supply and cutting the costs of hydropower and clean water for users downstream, and is designed to generate US$21.5 million in long-term benefits to Kenyan citizens, including farmers and businesses.
The overall aim of the project is to use readily available datasets coupled with targeted field studies to assemble evidence for key indicators of ecosystem services (ESS) sustainability and livelihood strategies in two sub-basins of the Tana Basin: Nyeri and Thika. Three specific research objectives are to
Evaluate past and present landscape land cover/land-use changes and how human activity has contributed to water and land degradation (specifically sedimentation) and thus a decline in ESS.
Quantify and map the flow of ESS through modeling tools best suited to analyzing multiple services and objectives in landscapes.
Identify and assess resource investment trajectories and how they relate to water and land degradation under current and future climate landscape and climate conditions.
The key study findings follow:
Change detection in the two watershed evaluations showed that most of the land cover classes experienced both gains and losses during the 2001-2013 period. The net change generated showed that tea and cereals were the biggest gainers, while forest and grassland were the biggest losers in terms of area occupied. However, spatially, the two watersheds are very dynamic with agricultural categories transitioning back and forth in the lowlands and conversion from natural areas mostly occurring on the boundaries of protected areas.
Climate suitability maps revealed that more areas will become suitable for both maize and beans, in particular to the west of the two watersheds under consideration, which is an area currently under tea production. This has implications as conversion from tea cover may increase overall runoff and reduce sediment retention in these areas. Areas currently covered by coffee, vegetables, and cereals will become more suitable for tea. Conversion of food crops to tea, an important cash crop in the region, may have a negative impact on food security.
Hydrological assessments revealed that consideration of point sources outside of agriculture is critical to assessing the overall landscape contribution of sediment in streams.
Hydrological modeling and land-use scenario generation also revealed that conversion of tea lands to agriculture and coffee will generate higher sediment loads into streams. Land cover classes covered by tea in both watersheds had the lowest sediment yields while land use under agricultural crops generated much higher sediment yields.
Without an adequate emphasis on maintenance and implementation of sustainable land management practices in the landscape, land-use changes will likely exacerbate the impact of sediment deposition in rivers and streams, which might further be accelerated by the projected 5% increment in future rainfall.
Scenario generation revealed that trade-off analysis between environmental integrity and population food security needs to be conducted in order to provide sustainable intervention options for both on-site and off-site beneficiaries under these changing landscapes.
The project contributes to the following CGIAR research programs: