California faces the prospect of significant water management challenges from climate change. The most certain changes are accelerated sea level rise and increased temperatures, which will reduce the Sierra Nevada snowpack and shift more runoff to winter months. These changes will likely cause major problems for flood control, for water supply reservoir operations, and for the maintenance of the present system of water exports through the fragile levee system of the Sacramento-San Joaquin Delta. Rising water temperatures also are likely to compromise habitat for some native aquatic species and pose challenges for reservoir operations, which must release cool water to support fish downstream. Although there is as yet little scientific consensus on the effects of climate change on overall precipitation levels, many expect precipitation variability to increase, with more extreme drought and flood events posing additional challenges to water managers.
Fortunately, California also possesses numerous assets – including adaptation tools and institutional capabilities – which can limit vulnerability of the state’s residents to changing conditions. Water supply managers have already begun using underground storage, water transfers, conservation, recycling, and desalination to expand their capacity to meet changing demands, and these same tools present cost-effective options for responding to a wide range of climate change scenarios. Many staples of flood management – including reservoir operations, levees, bypasses, insurance, and land-use regulation – are appropriate for the challenges posed by increasing flood flows.
Yet actions are also needed to improve response capacity in some areas. For water supply, a central issue is the management of the Delta, where new conveyance and habitat investments and new regulations are needed to sustain water supply reliability and ecosystem conditions. For flood management, studies to anticipate required changes have only begun, and institutional constraints limit the ability to change reservoir operations, raise funds for flood works, prevent development in flood-prone areas, and encourage use of flood insurance. Needed reforms include forward-looking reservoir operation planning and floodplain mapping, less restrictive rules for raising local flood assessments, and improved public information on flood risks. For water quality, an urgent priority is better science. Climate change is likely to have far-reaching implications for water regulations and management, but we remain at an embryonic state of knowledge about these future changes. We will have to make policy, planning, and operational decisions without perfect knowledge of how much the climate is changing.
Although local agencies are central players in all aspects of water management, adaptation will require strong-willed state leadership to shape institutions, incentives, and regulations capable of responding to change. Cooperation of federal agencies will be essential, given the important roles they play in flood management, environmental regulation, and water supply, particularly in the Delta.