Water resources vulnerability to climate change in the Upper Santa Cruz River, Arizona

In the Upper Santa Cruz River episodic streamflow events recharge a shallow alluvial aquifer, which is an essential water resource for the City of Nogales and surrounding communities. The complex natural variability of the rainfall-driven streamflow events introduces a water resources management challenge for the region. In this study, we assess the climate change projections of precipitation for the Upper Santa Cruz River from eight dynamically downscaled IPCC Global Circulation Models. Two models from the University of Arizona are downscaled simulations of carefully selected high performing Global Circulation Models for the region, and the other six are selected NARCCAP simulations. Our analysis of the eight selected dynamically downscaled climate model projections indicated an increase (decrease) frequency of occurrence of dry (wet) summers. The winter rainfall projections indicated an increase frequency of occurrence of both dry and wet winter seasons, which implies lower chance for a medium winter. The projected drying summers and increased winter inter-annual variability are expected to further complicate the water resources management task.