Combining hydroeconomic modelling and bottom-up approaches for climate change adaptation. Application to the Jucar river basin (Spain).

In many regions of the world, such as in the Southern Mediterranean area, water management has been challenging for long; however, climate change could act as an amplification factor and trigger an unprecedented situation. Several approaches have been proposed for the design of adaptation strategies for water resources systems. Although top-down approaches have been traditionally preferred, several authors have pointed out their relative lack of success when it comes to decision making. On the other hand, participative bottom-up approaches have the advantage of involving the stakeholders from the early stages of the strategy development, which could be crucial for the strategy's success. In order to overcome the shortcomings of both approaches and take advantage of their strengths, we propose a mixed bottom-up/top-down approach to define adaptation strategies at basin scale.

First, climate change impact on local water availability (future local inflows) is characterized using a top-down approach. Next, local knowledge is used through a participatory process in a bottom-up approach to foresight future scenarios of evolution of the agricultural sector and define locally relevant adaptation strategies. Each measure is characterized in terms of cost and efficiency. Water demands are characterized using economic demand curves. Finally, we used a hydroeconomic model to integrate the information obtained through top-down and bottom-up approaches to evaluate the net benefit of the different adaptation strategies, and select a socially acceptable and economically efficient program of measures for the climate and socioeconomic scenarios.

This methodology has been applied to the Jucar basin, a highly regulated basin with a fragile equilibrium between available water resources and demands. Climate change is expected to accentuate the current problems. The results show the importance of considering the spatial variability of climate change impacts in the basin. Temperature increase and precipitation decrease would be higher in the basin headwaters than in the coastal area, which conditions future inflows. In relation to adaptation measures, the stakeholders preferred the change from gravity to drip irrigation, the use of non-conventional water resources (wastewater reuse and desalination) and measures related to water governance. Finally, the results obtained from the hydroeconomic model show that, for most of the considered climate scenarios, the selected measures allow a significant reduction of the economic losses in the system.

Acknowledgements: This study has been supported by the ADAPTAMED project (RTI2018-101483-B-I00), funded by the Ministerio de Economia y Competitividad (MINECO) of Spain and with EU FEDER funds.