New Report Predicts Climate Change Will Significantly Impact California's Central Valley

Office of the Secretary

Sacramento and San Joaquin River Basins Impact Assessment Important Resource in President's Climate Action Plan

9/22/2014
Last edited 4/26/2016


WASHINGTON, D.C. – A new report released today by the Department of the Interior's Deputy Secretary Michael L. Connor finds that projected changes in temperature and precipitation, combined with a growing population, will have significant impacts on water supplies, water quality, fish and wildlife habitats, ecosystems, hydropower, recreation and flood control, in California's Central Valley this century.


"These projections by Interior's Bureau of Reclamation show the importance of President Obama's Climate Action Plan to address challenges like those California's Central Valley will face to provide a sustainable water supply for its citizens and economy," Connor stated. "As President Obama will emphasize once again at the UN Summit this week, climate change is not a problem we can leave to future generations to solve. The challenges to our water supplies illustrated in this study provide graphic examples of how acting now is an economic imperative as well as an environmental necessity."


The Sacramento and San Joaquin Basins Climate Impact Assessment projects temperatures may increase as the distance grows from the Pacific Ocean. Although most of the Central Valley may warm by 1°C in the early 21st century, a 2°C increase is projected by mid-century. Precipitation patterns indicate that there is a clear north to south decreasing precipitation trend compared to historical trends. In the northern parts of the Sacramento Valley there may be an overall increase to average annual precipitation.


"This assessment is one of several that studies climate risks to water supplies and related resources in river basins in the western United Sates," said Deputy Secretary Connor. “Although it is quite sobering to see the projections, we will follow up these assessments by continuing our work with the State of California and interested stakeholders to implement climate adaptation strategies in the Bay-Delta and other regions of the State. I am confident this ongoing collaboration along with the Climate Action Plan and the state's water action plan will help ensure that California has the necessary water supply to meet its future needs.”


The study released today presents an overview of the current climate and hydrology over the entire Central Valley including the Sacramento, San Joaquin and Tulare Lake basins. It also evaluates how projected climatic and hydrologic changes could impact water availability, management and demands while analyzing impacts of future urban growth and changes in land-use within the Central Valley.


Some findings of the Sacramento-San Joaquin Impact Assessment that show a potential for significant implications for water management, human infrastructure and ecosystems include the following:

  • Due to the warming conditions, the runoff will increase in winter and decrease in spring as more precipitation falls as rain instead of snow. Reservoirs may fill earlier and excess runoff would have to be released earlier to ensure proper flood protection is maintained. This may lead to reduced storage in reservoirs when the summer irrigation season begins.
  • Water demands are projected to increase. Urban water use is expected to increase due to population increases in the Central Valley while agricultural uses are projected to decrease because of a decline in irrigated acreage and to a lesser extent the effects of increasing carbon dioxide.
  • Water quality may decline by the end of the century. Sea levels are predicted to rise up to 1.6 meters in that time frame which will lead to an increase in salinity in the Delta and a decline of habitat for fish and wildlife. River water temperatures may increase because cold water availability from reservoir storage would be reduced.
  • The food web in the Delta is projected to decline. Projected lower flows through the Delta and reduced cold water due to lower reservoir levels will make less water available for species, including endangered species such as migrating salmon.
  • Hydropower generation is projected to decline in Central Valley Project facilities due to decreased reservoir storage. However, net power usage is also expected to decline due to reductions in pumping water and conveyance.



The climate projections utilized the Coupled Model Intercomparison Project Phase 3, CMIP3, climate projections with demographic and land use estimates based on the California Department of Water Resources Water Plan 2009.


This study supports the broader Sacramento and San Joaquin Basins Study, part of the Department of the Interior's WaterSMART Program. The basin study, which is expected to be completed in 2015, will provide additional analysis including the evaluation of adaptation strategies to mitigate impacts of climate change and meet future water demands. It will also update the climate projections using the recently-released Coupled Model Intercomparison Project Phase 5, CMIP5, climate projections and land use - demographic projections based on the recent California State Water Plan 2013 update, which were not available when the analysis was completed for this impact assessment.


"This study confirms that the current status quo for water supply in California is not sustainable," Deputy Secretary Connor said. "Reclamation and its partners in California are already developing solutions to meet the projected imbalances between future supply and demand within the Central Valley."


"The Sacramento and San Joaquin Basins Study will provide a roadmap forward for Reclamation and the State of California to ensure a sustainable water supply well into the future," Acting Reclamation Commissioner Lowell Pimley said.


The WaterSMART Program focuses on improving water conservation, sustainability and helping water resource managers make sound decisions about water use. It identifies strategies to ensure that this and future generations will have sufficient supplies of clean water for drinking, economic activities, recreation and ecosystem health. The program also identifies adaptive measures to address climate change and its impact on future water supply and demand.