ANALYSIS OF LARGE INFREQUENT (QUASI-DECADAL) GROUNDWATER RECHARGE EVENTS: A CASE STUDY FOR NORTHERN UTAH, UNITED STATES (Invited Presentation)

There has been a considerable amount of research linking climatic variability to hydrologic responses in arid and semi-arid regions such as the western United States. Although much effort has been spent to assess and predict changes in surface-water resources, little has been done to understand how climatic events and changes affect groundwater resources. This study focuses on characterizing and quantifying the effects of large quasi-decadal groundwater recharge events in the northern Utah portion of the Great Basin for the period 1960 to 2013. Annual groundwater-level monitoring data were analyzed with climatic data to characterize climatic conditions and frequency of these large recharge events. Using observed water-level changes and multivariate analysis, five large groundwater recharge events were identified within the study area and period, with a frequency of about 11 to 13 years. These events were generally characterized as having above-average annual precipitation and snow water equivalent and below-average seasonal temperatures, especially during the spring (April through June). Existing groundwater flow models for several basins within the study area were used to quantify changes in groundwater storage from these events. Simulated groundwater storage increases per basin from a single event ranged from about 115 Mm³ to 205 Mm³. Extrapolating these amounts over the entire northern Great Basin indicates that even a single large quasi-decadal recharge event could result in an increase of billions of cubic meters in groundwater storage. Understanding the role of these large quasi-decadal recharge events in replenishing aquifers and sustaining water supplies is crucial for long-term groundwater management.