Climate Change
Overview
Secretary of the Interior Ken Salazar released a report that assesses climate changes during the 21st century and how these might impact water operations, hydropower, flood control, and fish and wildlife in the western United States. The report to Congress, prepared by the Bureau of Reclamation, represents the first consistent and coordinated assessment of risks to future water supplies across Reclamation river basins, including those in the Mid-Pacific Region.
(For actions underway in the Region in reaction to this report, please see the next page: Climate Change Activities in 2012.)
Reclamation’s SECURE Water Act Report, released in 2011, identified the following likely climate changes, on average annually, in the Region:
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| Sacramento and San Joaquin River Basin |
Sacramento and San Joaquin River Basins
- Mean annual temperatures are projected to steadily increase by up to 5 degrees to 6 degrees Fahrenheit by the end of the 21st century throughout California’s Central Valley. These projections suggest that mean annual precipitation in the Sacramento and San Joaquin River basins will slightly increase by about 1 percent over the Sacramento River Basin and decrease by about 4 percent over the San Joaquin River Basin by 2050. By the end of the 21st century, the projections indicate a precipitation decline of about 3 percent to 5 percent in the northern and about 8 percent to 10 percent in the southern portions of the Central Valley.
- Runoff is projected to increase slightly during the first half of the 21st century and decline slightly in the latter half of the century.
- As the climate warms, more precipitation falling as rain instead of snow at lower elevations will increase winter runoff and decrease summer runoff. The increase in temperature also will result in significantly decreased snowpack at higher elevations.
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| Klamath River Basin |
Klamath River Basin
- Mean annual temperatures in the Klamath River Basin in southern Oregon and northern California is projected to increase by about 5 degrees to 6 degrees Fahrenheit during the 21st century, with a projected increase of about 2 percent in precipitation by 2050 and a slight decline of about 1 percent by the end of the century.
- Runoff is projected to increase anywhere from 3 percent to 10 percent by 2050 and by the end of the century, range from a 1 percent decrease to about a 4 percent increase.
- Increased warming is expected to reduce snowpack and snowmelt, resulting in less runoff during the late spring through early autumn. Snowpack decreases are projected to be more substantial in the warmer parts of the basin.
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| Truckee River Basin |
Truckee River Basin
- Mean annual temperatures in the Truckee River Basin in the Sierra Nevada range of California and Nevada are projected to increase by about 3 degrees to 5 degrees Fahrenheit during the 21st century, with a decrease in precipitation of about 1 percent by 2050 and 3 percent to 5 percent by the end of the century.
- Runoff is projected to decrease by about 3 percent to 5 percent by 2050 and 3 percent to 6 percent by the end of the century.
- Warmer conditions will likely turn snow into rain, increasing December–March runoff and significantly decreasing April–July runoff.
Climate Change Activities in 2012
The following actions are underway in the Mid Pacific Region:
- During Fiscal Year 2012, three basin studies were underway to address climate impact assessments and develop adaptation strategies for each of the major Mid-Pacific Region river basins identified in the Secure Water Act of 2009.
- The West-wide Climate Risk Assessment is continuing to establish a better foundation for developing more in-depth analyses of climate impacts and adaptation strategy options for the basin studies, operations planning and other activities. In FY 2012, new information and improved methods to evaluate the climate change impacts on agricultural water demands during the 21st century have been developed for use in the Sacramento-San Joaquin Basins Study.
- The Region is also conducting other planning studies that include assessments of the effects of climate changes. These include the Bay Delta Conservation Plan, CALFED Bay-Delta Program, storage program investigations, and the Central Valley Project Integrated Resource Plan.
February 22, 2013