Ancient Groundwater Studies Reveal Climate Vulnerabilities in U.S. Regions

Woods Hole, Mass. (June 17, 2025) — New research from the Woods Hole Oceanographic Institution (WHOI) has unveiled significant climate vulnerabilities in the groundwater systems of the United States, particularly between the Southwestern U.S. and the Pacific Northwest. The study, published in the journal *Science Advances*, highlights how ancient groundwater records from the last ice age reveal distinct responses in groundwater levels to climatic changes that continue to shape these regions today.

During the last ice age, the now-arid Southwestern U.S. experienced intense storms, while the currently rainy Pacific Northwest remained relatively dry. As global temperatures increased and ice sheets receded, these storm patterns shifted northward, resulting in a transformation of climate dynamics. According to Alan Seltzer, an associate scientist at WHOI and lead author of the study, "On average, climate models suggest the Southwestern U.S. may get drier while the Pacific Northwest may get wetter by the end of the century."

The research team, which included seven WHOI-affiliated scientists, analyzed fossil groundwater data from 17 wells across Washington and Idaho, dating back to approximately 20,000 years ago. They employed a novel isotopic method to measure noble gases—specifically xenon and krypton—to assess past water table depths, revealing that groundwater levels in the Pacific Northwest remained stable despite increased precipitation, while the Southwest saw a notable decline in groundwater resources.

"Going back in time to large amplitude changes helps us understand the behavior of a system, like groundwater, which we may struggle to capture with short modern records," Seltzer stated. Modern groundwater records have been complicated by human activity and are limited to recent centuries, making this ancient data invaluable for assessing long-term trends in groundwater dynamics.

The implications of this study extend beyond the U.S., as the researchers also mapped areas globally that may face heightened water insecurity in the future. Kris Karnauskas, an associate professor of Atmospheric and Oceanic Sciences at the University of Colorado Boulder and co-author of the study, noted, "By going beyond just precipitation, these results should help direct research and adaptation efforts to regions with heightened water insecurity in the future."

The findings underscore the critical role of groundwater as Earth's largest source of usable freshwater, essential for drinking, agriculture, and industry. With millions of wells at risk of drying up due to climate change, understanding groundwater responses to long-term climatic shifts is vital for future planning.

The study not only emphasizes the vulnerability of Southwestern aquifers but also exemplifies how integrating paleoclimate data with modern models can enhance water resource planning globally. The research team’s approach to utilizing ancient water table records alongside Earth system models yielded consistent results, validating their findings and suggesting that even simple groundwater models can capture key dynamics effectively.

This research builds on previous studies, including an associated study on fossil groundwater led by Seltzer's lab in collaboration with the University of Manchester, published in *Nature Geoscience*. This earlier work focused on geological insights from ancient groundwater in the Pacific Northwest, analyzing groundwater from the Palouse Basin Aquifer and employing innovative techniques to detect volcanic gas inputs, despite the region’s lack of modern volcanic activity.

As climate change continues to impact regional hydrology, the need for a comprehensive understanding of groundwater systems becomes increasingly urgent. The research findings are timely, as policymakers and resource managers consider strategies for sustainable water management in the face of evolving climate conditions.

In conclusion, understanding the historical context of groundwater dynamics, as illuminated by this recent study, is essential for addressing future challenges related to water security and climate resilience, particularly in vulnerable regions across the globe.