Water storage ‘crucial’ for American River Basin
The U.S. Bureau of Reclamation has released a study on the American River Basin that shows how changing climate could affect future water supplies.
The study projects increases in temperatures of 4-7 degrees Fahrenheit by the end of the 21st century, depending on the season.
Hydrologic impacts show an increase in runoff during fall and winter while spring and summer showed a decrease in runoff.
Warmer temperatures are driving earlier snow melts in winter rather than summer and the lost volume of runoff will affect water operations, said U.S. Bureau of Reclamation Hydrologic Engineer Ian Ferguson during a virtual press conference last week.
Precipitation is projected to be increasingly variable into the future with the timing of the moisture shifting with fall and spring precipitation declining and winter and summer precipitation increasing. In addition, the snowpack will decrease due to warming, moving the peak runoff by more than a month by the mid to late century.
Lower storage levels are expected as snowfall will be replaced with rain, which will make it harder to operate Folsom Lake and manage the American River for drought and flood control.
Water temperatures and ecosystems would be impacted as well. Three scenarios show average water temperatures in August months will increase by 4-10 degrees due to a combination of reduced reservoir storage, less cold water available for water temperature management and rising air temperatures.
Without any adaptation strategies the study projects an increase of 10,000-30,000 acre-feet per year in supply-demand imbalances across all users within the basin.
The study identified five major stressors in the basin — population growth, climate change, ecosystem degradation, regulatory interventions (such as the Sustainable Groundwater Management Act) and social values and preferences.
A number of vulnerabilities throughout the basin related to Folsom Reservoir include its relatively small capacity compared to its average annual inflows and competing priorities for flood control, water supply and ecosystem protection.
In relation to the foothills, limited groundwater, shrinking snowpack, decreasing runoff during fall and summer and increased forest fires are all vulnerabilities the region faces.
Different strategies to reduce current and projected supply-demand imbalances are being implemented, including the possibility of conducting a feasibility study for Alder Creek to evaluate high-elevation, off-stream storage as a potential replacement for lost storage due to reduced snowpack and earlier snowmelt runoff.
Ken Payne, general manager of the El Dorado County Water Agency and advocate for the storage replacement, said alternative plans are needed.
“We have lots of farmers who are going to be fighting for this water,” Payne said, whose agency helped work on the study. “It is crucial we get storage to replace the reliance on the snowpack to sustain the county’s water needs.”
Other mitigation efforts include the use of existing diversion facilities on the Sacramento River and exchanging water supply to reduce reliance on Folsom Lake and the American River, a $300 million water bank in development in the Sacramento area and releasing flood water to recharge groundwater to create additional regional water supply and ecosystem benefits.
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