From local knowledge to decision making in climate change adaptation at basin scale. Application to the Jucar River Basin, Spain

Climate change is challenging the conventional approaches for water systems planning. Two main approaches are commonly implemented in the design of climate change adaptation plans: impact-oriented top-down approaches and vulnerability-oriented bottom-up approaches. In order to overcome the shortcomings of both approaches and take advantage of their strengths, we propose an integrative methodology to define adaptation strategies at basin scale, identifying and combining potential changes in water demand and water supply infrastructure along with climate variability and change. The impact of climate change on future local water availability is assessed applying a top-down approach. Local knowledge is used through a participatory bottom-up approach to foresee future scenarios of evolution of the agricultural sector and agricultural water demand, and to identify locally relevant adaptation strategies. A hydroeconomic model integrates the information from both approaches to identify a socially acceptable and cost-effective program of measures for each climate scenario. This method was applied to the Jucar basin, a highly regulated basin with a tight equilibrium between water resources and demands. The results show an important variability of climate change impacts across the basin, with main inflow reductions in the headwaters. The stakeholders prioritized the adaptation options of change to drip irrigation, use of non-conventional resources, and changes in water governance. The results obtained from the hydroeconomic model show that the portfolio of selected adaptation measures could significantly reduce the system’s average annual deficit and cost.