Impacts of Surface Water Access, Legislation, and Drought on Groundwater in the Southwestern U.S. at Multiple Scales

Abstract

Groundwater is a critical resource for ecosystems and human societies, especially in arid and semi-arid regions. Yet, as climate change intensifies and human water demands grow, groundwater systems are under increasing stress. This dissertation explores groundwater trends across Arizona, with a particular focus on the intersection of hydrology, drought, policy, and human decision-making. Through an interdisciplinary lens that integrates satellite data, groundwater well observations, geospatial analysis, and water governance frameworks, this work provides a holistic assessment of shallow and deep groundwater patterns and the human systems that shape them.Chapter 1 examines long-term trends in groundwater depth and well drilling using a statewide well database and satellite-derived total water storage data. Results show that while groundwater declines are widespread, recovery is localized and primarily driven by managed aquifer recharge using imported surface water from the Colorado River rather than regulatory limits on pumping alone. Chapter 2 shifts focus to shallow groundwater, a vital component for streamflow and groundwater-dependent ecosystems. Despite Arizona's aridity, shallow groundwater was historically widespread. However, it has declined significantly since the 2000s. In nine of the thirteen major watersheds, shallow groundwater loss coincides with increasing stream intermittency, suggesting growing risks to surface water systems. Chapter 3 explores how drought compounds groundwater declines. Using well data from 2000–2022 and multiple case studies, this chapter shows that while drought can accelerate depletion, the severity of impact varies. Regions with groundwater regulation, access to surface water, or robust conservation efforts experienced more muted responses or even temporary recovery during drought periods. Collectively, this research reveals that human decisions particularly related to surface water imports, managed recharge, and local policy play a critical role in shaping groundwater outcomes, sometimes more so than climate or geology. Protecting shallow groundwater and diversifying water portfolios are key strategies for resilience. These findings offer valuable insights not only for Arizona, but for arid and water-stressed regions worldwide navigating an uncertain hydrologic future.