The University of Montana Western Environmental Science Department is proud to host Matthew Swarr as part of the “On the Rocks” lecture series. Swarr will present “Exploring the Evolution of Water Resources in the Western U.S. Using Space Geodesy” on Wednesday, March 26, from 4:00-5:00 p.m. in UMW’s Lucy Carson Library.
Matthew Swarr is currently a Ph.D. candidate at the University of Montana studying water resources using geophysics. His research uses high-precision GPS (the same technology your phone uses!) to measure changes in the Earth’s shape produced by gains and losses of water storage near the Earth’s surface. His research has taken him all over the western U.S., from the deeply wooded Bitterroot Mountains of Idaho to the high peaks of the Sierra Nevada.
Presentation Abstract:
Mountainous regions act as natural “water towers” by capturing freshwater during winter months and delivering it to low-elevation communities through streamflow generation and subsurface groundwater flow. However, the western U.S., coming out of the driest 20-year period of the last 1,200 years, faces challenges in that persistent declines in mountain water storage have been observed across the region over the past two decades, driven by warming air temperatures and variable winter conditions.
Initial forecasts indicate that climate change could further exacerbate mountain water loss, threatening the sustainability of ecosystems and impacting resources relied upon by our society. However, shifts in precipitation as a result of climate change are predicted to become increasingly variable in the coming years, potentially supporting water storage in mountainous regions through extreme precipitation events such as atmospheric rivers. These events can channel significant quantities of water vapor through the atmosphere before being deposited in mountainous regions.
Using high-precision Global Positioning System (GPS) surface displacements that reflect the solid Earth’s deformation response to loading and unloading, we quantify changes in water storage within the western U.S. over the past two decades, identifying significant periods of drought and recovery. Using our GPS estimates of water storage, we infer changes in groundwater storage within the Sierra Nevada of California and the Cascade Range of California, Oregon, and Washington, finding diminishing groundwater to be the dominant source of long-term water storage loss within both regions.
Despite these findings, we find that periods of extreme precipitation, such as the winter of 2023, can significantly restore water lost during severe droughts. The gains associated with these wet periods are durable, persisting over several subsequent years despite modest winters following an extremely wet year. This indicates that brief but extreme precipitation events can provide refuge for adjacent lowland regions dependent upon mountain groundwater for several years post-event.
In a future with increasingly variable precipitation, the strong influence of these extreme events may act to maintain mountain groundwater, sustain ecosystem health, and buffer adjacent areas against drought conditions during dry periods.
For more information on UMW’s “On the Rocks” series, please contact UMW Associate Professor of Environmental Sustainability, Dr. Arica Crootof, at arica.crootof@umwestern.edu.
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