California's Water: Facts on Climate Change

Climate Change Facts

• There is growing evidence that climate change is occurring, and a likely impact on California will be a shift in our rain and snowfall patterns over the next few decades.

• The shift could lead to a significant reduction in the Sierra snow pack – California’s largest and most important reservoir.

• Some scenarios suggest that as patterns shift, more precipitation will fall as rain instead of snow, resulting in earlier runoff and potentially producing floods far greater than what California has experienced in modern times.

• Climate change already appears to causing sea level to rise in some areas. In California, sea level rise could affect sensitive ecosystems and put additional pressure on aging Delta levees.

Snow Pack Issues

• California relies on the snow pack for a major part of its water storage. Annual runoff from the Sierra during April-July averages 14 million acre-feet a year – mostly from snowmelt.

• Some climate change models show that climate change could significantly reduce the snow pack in the future, thereby diminishing the state’s total water storage capacity. One scenario showed a 2-degree rise in average temperatures could reduce annual runoff by 52%. A 2-degree rise is well within the 1.4-degree to 5-degree increase predicted by some models.

• Since our existing reservoirs and flood control facilities were built to accommodate gradual runoff of melting snow, these changes could have a major impact on our water supply system and our flood management capability.

Sea Level Issues

• Sea level as measured at the Golden Gate has risen more than six inches since the early 20 th century. Models predict a median rise of another 1.6 feet over the 21 st century due to climate change.

• In the Delta, some researchers believe sea level could rise as much as 12-16 inches over the coming decades.

• Sea level rise would have a serious effect on the Delta. It could disrupt ecosystems, undermine wetlands restoration efforts, and put even more pressure on the Delta’s fragile levee system, putting at risk the water supply for about 22 million Californians and millions of acres of irrigated farmland.

• Some models show that a single-foot rise in sea level rise in the Delta would increase the frequency of extremely high tides in the Western Delta and increase salinity intrusion from the ocean, degrading freshwater supplies exported from the Delta unless more fresh water is released from upstream reservoirs.

• Coastal aquifers also could be threatened.