RAPID: Quantifying timescales of groundwater recharge and discharge in seasonally snow-covered headwater catchments

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One of the largest challenges in efficient and equitable water resource management in the western US is the high spatial and temporal variability in streamflow. Although total winter snowfall is the primary driver of streamflow, the relationship between winter snow and river discharge is becoming ever more variable as temperatures warm and precipitation patterns change. This variability is highlighted by Spring runoff in the upper Colorado River Basin during 2020 and 2021, where annual snowfall was close to average, but annual streamflow was much lower than expected. Recent work has demonstrated that a major cause of this variability is groundwater storage that responds to climate over multiple years. This project will provide baseline data to determine how and why regional groundwater storage varies, ultimately allowing resource managers and water users to anticipate and plan for annual water supply months to years in advance, eliminating surprises due to having either too much, or more often too little water to meet demands.This project will directly address the implicit assumptions of water balance closure on an annual time scale. The work builds on decades of hydrochemical research that demonstrates snowmelt-derived streamflow consists primarily of “old” water and that variability in this old water is significantly related to variability in runoff efficiency. Sample collection and analyses using state of the art age tracers (e.g. 3H, 3H/3He, SF6), water isotopes, and major ion chemistry during this project will begin to elucidate the mechanisms underlying these relationships and how they vary with landscape structure, underlying geology, and climate. The work focuses on extensively studied catchments in Utah as well as research catchments (CZCN, CZO, USFS, USDA ARS, USGS) throughout the western US. Ongoing partnerships with resources managers in Utah, Arizona, Colorado, and New Mexico will facilitate translation of knowledge gained into application.This award is co-funded by the Hydrologic Sciences and Critical Zone programs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.