Re-framing the decision context over trade-offs among ecosystem services and wellbeing in a major river basin where water resources are highly contested

Water resources and water-related ecosystem services are vital to social-ecological systems, yet in many parts of the world water as a finite resource is revealed by its unsustainable and inequitable use. Increased threats to water security and supply of ecosystem services arise due to increasing and contested demand and declining supply due to climate change and other stressors. Trade-off decisions need to be made between competing sectors of food production, hydropower generation and environmental needs: the water-food-energy-environment nexus. New approaches are needed to address how water resources and ecosystem service benefits are shared among competing interests. One approach involves changes to decision contexts, shaped by the values, rules and knowledge which decision makers draw upon when considering options. By changing decision contexts, new opportunities become available. Here, we describe Nexus Webs; a knowledge framework designed to promote collaborative exploration of synergies and trade-offs and enable changes in decision contexts for water use. As part of the process of shifting this framework from concept to operation, we apply Nexus Webs to contrasting water use scenarios in the Pangani Basin (Tanzania and Kenya), where water is over-allocated and highly contested. Under each scenario, we detail linkages between different water uses and their effects on assets (ecosystems, biodiversity and built infrastructure), the effects on assets for the supply of ecosystem services and how these affect livelihoods and wellbeing. We outline how Nexus Webs can be developed and used to change the decision context to consider options for more socially inclusive and equitable use of water resources.