Targeting and valuing conservation investments in support of a water fund: linking upstream land management with downstream services in the Upper Tana catchment, Kenya

We apply an integrated modeling framework to both target and value watershed management interventions in the Upper Tana watershed, which provides municipal water, irrigation water, and hydropower services to Nairobi and surrounding areas. The analysis begins by applying an index model approach that incorporates existing land use and land surface characteristics to prioritize the type and location of conservation investments in different subbasins, subject to budget constraints and stakeholder concerns (Resource Investment Optimization System -- RIOS). We then run the Soil and Water Assessment Tool (SWAT) using the RIOS-identified investment scenarios to produce spatially explicit scenarios that simulate changes in water yield and suspended sediment. Finally, we link those biophysical outputs to monetary and non-monetary human well-being metrics for multiple benefit streams, including: Reduced water treatment costs, increased hydropower production, and crop yield benefits for upstream farmers in the conservation area. The viability of a payment for watershed services scheme is discussed, with attention to the various components of value assessed and to dependencies on water management approaches. While other studies have examined links between land use and the provision of hydrologic services, this study is novel in that it presents an integrated analysis that targets interventions in a decision context and then relies on calibrated, process-based, biophysical models to demonstrate the return on those investments considering multiple (and sometimes competing) hydrological services, doing so at a sub-annual time-scale.