Design and impact assessment of watershed investments: An approach based on ecosystem services and boundary work

Watershed investments, whose main aim is to secure water for cities, represent a promising opportunity for large-scale sustainability transitions in the near future. If properly designed, they promote activities in thewater- shed that enhance ecosystem serviceswhile protecting nature and biodiversity, aswell as achieving other soci- etal goals. In this paper,we build on the concepts of ecosystemservices and boundarywork, to develop and test an operative approach for designing and assessing the impact of watershed investments. The approach is struc- tured to facilitate negotiationsamong stakeholders. Its strategic component includes setting the agenda; defining investment scenarios; and assessing the performance ofwatershed investments as well as planning for a follow- up. Its technical component concerns data processing; tailoring spatially explicit ecosystem service models; hence their application to design a set of “investment portfolios”, generate future land use scenarios, and model impacts on selected ecosystem services. A case study illustrates howthe technical component can be de- veloped in a data scarce context in sub-Saharan Africa in a way that is functional to support the steps of the stra- tegic component. The case study addresses soil erosion andwater scarcity-related challenges affecting Asmara, a medium-sized city in Eritrea, and considers urbanwater security and rural poverty alleviation as two illustrative objectives, within a ten-year planning horizon. The case study results consist in spatially explicit data (invest- ment portfolio, land use scenario, impact on ecosystemservices),whichwere aggregated to quantitatively assess the performance of differentwatershed investments scenarios, in terms of changes in soil erosion control. By ad- dressing stakeholders' concerns of credibility, saliency, and legitimacy, the approach is expected to facilitate ne- gotiation of objectives, definition of scenarios, and assessment of alternativewatershed investments, ultimately, to contribute to implementing an adaptivewatershed management.