Warming and Snow Loss Increase Reliance on Old Groundwater in a Colorado River Headwater

Warming temperatures and decreasing snowfall are changing the way water moves through the headwaters of the Colorado River. While previously restricted due to a lack of data in mountain systems, this study uses a combination of new field observations, modeling, and data analysis to investigate stream water source. Results show that in low-snow years, the region relies more on older groundwater, and that this reliance increases as temperatures rise. This shift can affect the long-term sustainability of the water supply in the western United States.

Effective management of mountain streamflow is crucial to ensure the long-term sustainability of water resources in the western US. The increased reliance on old groundwater due to warming and snow loss has significant implications for the Colorado River headwater’s water sustainability. Older groundwater may not be replenished as quickly as newer sources, potentially leading to deeper water tables, altered ecosystems, and impacts to water quality. The findings can inform policy decisions and help water managers develop effective strategies to mitigate the effects on groundwater resources.

This study found that old (>3 y) groundwater buffers mountainous streamflow, which is exacerbated in low-snow years and with warmer air temperatures. for every 1°C increase in temperature, the stream’s reliance on old groundwater increases by 15%. As streamflow declines with warming, the age of groundwater supporting it gets older, in part due to intermediate-aged (1-3 year) groundwater declining twice as fast. Notably, groundwater losses are most pronounced at the highest elevations with warming. These changes indicate a significant shift in the region’s water sources, potentially threatening the long-term sustainability of the water supply.