Rural Water Supply Drought Vulnerability Assessment in the Desert Southwest
University of Arizona, Water Resources Research Center
Groundwater is the sole source of water supply for many rural agricultural communities in Arizona. Groundwater age dating has characterized most regional aquifers as containing waters that had originally recharged the system thousands of years ago, under the colder and wetter climate of the Pleistocene. For aquifer waters thousands of years old, planned depletion of this non-renewable resource appears the norm. Several communities in Arizona, however, are sustained by groundwater of recent age, having fallen as rain or snow within the conditions of our modern climate. These younger aquifer systems are more vulnerable to drought as recharge rates decrease, but this vulnerability could be offset by the opportunity to change future water resource management strategy to increase drought preparedness and community resilience. The isolated aquifer system of the Arivaca (Pima County) groundwater basin supports more than 200 wells, lush riparian habitat, perennial streamflow and a cienega in the midst of the southern Arizona Sonoran Desert. Initial age-dating suggests groundwater is approximately 40 to 50 years old with apparent monsoonal recharge. Sufficient climate, streamflow, and groundwater elevation data exist to allow for the determination of climate-groundwater relationships, allowing us to characterize the relationship between drought and aquifer sustainability over the past 50 years. Armed with this vulnerability characterization and assessment approach, we are assisting in identifying opportunities for the community to initiate management strategies for the future to address climate change. Expanded sampling for isotopic signatures and metering of selected water wells, coupled with time-series analysis of existing climate data, has allowed us to refine our understanding of water supply vulnerability in the arid desert of the southwest. This study has allowed us to expand fundamental knowledge of climate-groundwater relationships in young arid aquifers and proposes an innovative approach to quantifying water supply vulnerability based on groundwater age and recent climate data. As a result of this drought vulnerability assessment, recommendations as to future resource management options are being implemented, and this vulnerability assessment tool is being applied to other rural communities across Arizona.