Long-term sustainability of large water resource systems under climate change: A cascade modeling approach

The Pyrenees are the main source of water for a large region in Southern Europe. In recent decades, streamflow and snow accumulation in these mountains have decreased, and climate models predict that further reductions in water will threaten the sustainability of downstream regions. This article presents a cascading multi-model and multi-scenario approach to assess how future climate change may affect the hydrology and water management of Pyrenees-dependent systems. In particular, we combined future climate projections and management scenarios and applied them to the Gállego-Cinca River System in the Ebro River Basin of Spain. We developed a hydrologic model for the headwaters of this system (the source of most of the water), and then used a management model to simulate reservoir operation and water allocation among the different agricultural demand units of this system, the largest irrigated region in Spain. We assessed future headwater streamflow for 22 climate models, and translated this climate signal into a management model by using a delta change approach. Finally, we evaluated the performance and sustainability of the system with indicators based on the frequency, duration, and magnitude of the supply deficit. The results show that use of the current planned management scenarios will threaten to the system's future sustainability, especially for irrigated agriculture. These results indicate a need to revise current water resource planning strategies in this region, and to establish long-term, robust, and sustainable measures for adaptation to climate change.