California & Climate Change

Today, millions of Californians rely on an engineered delivery system that is being pushed beyond its limits. How we respond and adapt to those changes could be the greatest economic and environmental challenge of this century.

Global climate change has affected California's natural systems. Warmer conditions have significant hydrologic, water use, and ecological implications. Precipitation and runoff patterns are changing, increasing the uncertainties for water supply and quality, flood management, and ecosystem functions. Loss of mountain snowpack is significant, and peak river flows occur earlier in the spring. Sea level rise has begun to disrupt ecosystems and communities in coastal areas. Some of the biggest impacts are felt in the Sacramento-San Joaquin Delta where levees protect low-lying islands. New water management approaches and methods are needed to deal with these changes.

California has a history of naturally and widely varying hydrologic conditions, including recurring and extended droughts. Climate change and variability are having impacts not yet fully understood, making historic hydrologic patterns unreliable in forecasting the state's water future. At the same time, an array of complicated issues confronts water managers, who must deal with competing interests to provide water to farms, businesses, and homes, while complying with legal and regulatory requirements:

• The hub of the state's water supply and delivery system, the Sacramento–San Joaquin Delta, faces serious ecosystem problems that threaten supply reliability and quality.
• The snow-water equivalent in California’s Water Year 2014 (October 1, 2013 through September 30, 2014) was a record low at slightly less than 25 percent of normal. In the current year, the snow pack was less than half of where it was in 2014 (~9 percent). 
• Groundwater supplies are falling with drought and increasing demand, as surface water from snowpack runoff is less available because of less precipitation and more water is taken from wells.
• Warming temperatures and changes in rainfall and runoff patterns will exacerbate the frequency and intensity of droughts.
• Delta levees are aging, impacting flood risk.
• Rising snowlines caused by climate variability and change will allow more of the Sierra Nevada watersheds to contribute to peak storm runoff, with a potential increase in flood events.