Green Water Credits – exploring its potential to enhance ecosystem services by reducing soil erosion in the Upper Tana basin, Kenya

摘要

Food production, water availability and energy production are important ecosystem services of the Upper Tana basin (Kenya) and they decline due to upstream erosion affecting downstream water users. The effect of 11 soil conservation measures on soil erosion and the three ecosystem services was estimated by a modelling approach to assess agro-ecological processes and benefit/cost relations. Soil water available for evaporation and transpiration (‘green water’) functioned as a unifying concept to express the effects of erosion and the impacts of soil and water conservation measures that result in: (1) increased water availability for crops; (2) increased fluxes towards aquifers, thereby increasing water supply and regulating streamflow, and (3) a reduction of erosion and siltation of reservoirs used for hydroelectricity. Modelling indicated that the three ecosystem services could be improved, as compared with the base level, by up to 20% by introducing appropriate conservation measures with benefit/cost relations of around 7. However, farmers were unable to make the necessary investments and much effort and many institutional studies were needed to achieve progress towards implementation by initiating the Green Water Credits (GWC) programme intended to arrange payments by downstream businesses to upstream farmers. A timeline analysis is presented to illustrate the slow, but persistent, development of transdisciplinary activities as a function of time using connected value development as a guiding principle.