Aquifer Vulnerability to Climate Variability: Groundwater Age Dating to Identify Resource Sustainability

Climate directly influences the amount of water recharged into aquifers by controlling the amount and seasonality of precipitation and evapotranspiration. In the arid southwestern United States, groundwater resources are being consumed at a rate that exceeds recharge. Carbon-14 based age-dates of central Arizona basin fill aquifers indicate that recharge likely occurred at the end of the Pleistocene when the climate was colder and wetting than the current era. The cities of Phoenix and Tucson are pumping groundwater thousands of years old, while aquifers tapped by some remote rural communities in Arizona, however, exhibit recent aquifer recharge.  These younger aquifer systems are more responsive to climate variability and change and therefore are more vulnerable to drought. This vulnerability can be offset, however, by a change in water resource management strategy.  Municipalities with abundant economic and knowledge resources can fund detailed research studies quantifying water budgets, but such studies are often unavailable to small, rural communities. Rapid assessments of groundwater character and its connection to climate can provide valuable information to local water managers and citizen groups.  These assessments, built on relatively inexpensive isotope geochemistry analyses of samples from volunteered domestic well have the additional advantage of encouraging a water management ethic in the citizens participants. Investigators performed the first rapid assessment of groundwater vulnerability to climate variability using this inexpensive, interactive method in Arivaca, Arizona, where the community responded to the surprising results with increased interest in managing their water for sustainability in the face of climate variability and change. To further the role of science-based decisions in development planning, communities along the Agua Fria River north of Phoenix also participated in our rapid assessment of groundwater age and aquifer vulnerability, demanding recognition of their water resource vulnerability from their political leaders.