The American River Basin in central California is expected to experience rising temperatures and a declining snowpack through the end of the 21st century, according to a study released by the Bureau of Reclamation.
The American River Basin Study also found an increased variability of fall and winter precipitation that will amplify the severity of droughts and flooding in the basin.
The American River Basin and the area covered by this study consists of 3,600 square miles in central California from the valley through the foothills to the top of the Sierra Nevada. It includes the city of Sacramento and the surrounding area. Folsom Dam and Lake – which straddles Sacramento, Placer and El Dorado counties – is one of the facilities affected, with its 198.72 MW hydroelectric powerhouse.
The study found that maximum temperatures are projected to increase, with the most significant increase of 7.3 degrees Fahrenheit during the summer months by the end of the 21st century. Projections of average annual precipitation are uncertain, but climate projections indicate a change in precipitation timing and variability. 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.
Adaptation strategies are under way to increase agricultural and urban water use efficiency, among other strategies. New adaptation strategy portfolios were also developed for further evaluation by Reclamation and its collaborators to maintain a balance between supply and demand.
For example, one adaptation portfolio highlights the importance of long-term Central Valley Project contracts for regional reliability. Other adaptation portfolios included evaluating:
- Use of high elevation, off-stream storage to replace lost storage from reduced snowpack and earlier snowmelt.
- Use of existing diversion facilities on the Sacramento River and exchange water supply to reduce reliance on Folsom Reservoir and the American River.
- Raising Folsom Dam to increase flood control space.
- Releasing flood water earlier to recharge groundwater and create additional regional water supply.
- The effectiveness of the flow management standard for the Lower American River in the 2015 update of the Sacramento Water Forum Agreement to reduce the effects on the river’s ecosystem and fisheries from climate change.
“Water management in the basin is expected to be more challenging in the future due to climate pressures that include warming temperatures, shrinking snowpack, shorter and more intense wet seasons and rising sea levels,” said California-Great Basin Regional Director Ernest Conant. Reclamation will work with its partners “on the identified adaptation portfolios to address the vulnerabilities and maintain a balance between supply and demand in the basin,” he said.
The basin study was selected in 2017 and built upon the Sacramento and San Joaquin Rivers Basin Study completed in 2016.
Reclamation developed the study in collaboration with the Placer County Water Agency, City of Roseville, City of Sacramento, El Dorado County Water Agency, city of Folsom and Regional Water Authority. The non-federal partners also coordinated with the Sacramento Area Flood Control Agency to address flood risks.
Other contributors to the report included the California Department of Water Resources, University of California-Davis, The Water Forum, Sacramento Municipal Utility District and El Dorado Irrigation District.
