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Communities and agricultural operations across the Western United States depend heavily on snowmelt from mountain ranges to sustain water supplies each spring. Traditional models have assumed that only a small portion of this snowmelt infiltrates into the ground, with the majority quickly flowing into rivers and creeks. However, new research from University of Utah hydrologists paints a far more complex picture of how mountain water moves.
According to a recent study led by geologist Paul Brooks, most of the streamflow that fills reservoirs each spring actually consists of water that has been stored underground for several years. The team found that, on average, a snowflake falling in the mountains takes more than five years to emerge as streamflow—sometimes as long as 15 years. This discovery challenges long-standing assumptions and reveals a significant, previously underappreciated underground water reserve.
"Our current models tend to underestimate just how much water is stored beneath the surface," said Brooks. "Most of the snowmelt infiltrates into the ground and lingers there before making its way into streams or being absorbed by vegetation."
To trace the age of the water, Brooks and his colleagues collected runoff samples from 42 sites across the western U.S. and used tritium isotope analysis to determine how long the water had been underground. Their findings, published in Communications Earth & Environment, were co-authored by University of Utah professors Sara Warix and Kip Solomon, along with collaborators from across the region.
The data revealed that mountain groundwater storage plays a far greater role in supplying streamflow than previously recognized, highlighting the importance of reevaluating how water resources are managed—especially as climate patterns shift.
"We're entering an era when old assumptions no longer hold," said Warix. "If most of our streamflow is years-old groundwater, then any changes in climate or land use won't show up immediately. There will be delayed responses, which must be taken into account for effective water planning."
Brooks carried out the sampling in 2022 during a sabbatical, collecting water during both midwinter base flow conditions and spring runoff. The sites stretched from the Colorado Front Range to the Sierra Nevada’s eastern slopes, covering parts of Idaho, Wyoming, Utah, Colorado, California, and New Mexico—regions that feed five major river systems.
Utah, in particular, provided valuable long-term data, with streamflow records going back more than a century. This unique dataset has allowed scientists to track long-term trends and cycles that would otherwise be obscured. Ultimately, the study underscores the need to revise hydrological models to account for substantial groundwater storage in mountainous regions, which could be crucial for managing future water resources amid accelerating climate change.
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Post time 2025-05-06 17:39:08