California's Trouble: Rising Seas, Floods and Drought in Forecast

California has a big water problem -- and global warming will only make that problem bigger. Three-quarters of our precipitation falls in the winter, almost all in the northern half of the state, although most of the population and a great deal of the agriculture are in the south. The current system of capturing and transferring water through the Sacramento-San Joaquin Delta to the areas of greatest demand is unsustainable, and climate change will only exacerbate the crisis.

According to the state's Climate Action Team, global warming is likely to play out in California's water system in two major ways: a smaller snowpack will reduce our ready water supply, and wilder weather will heighten the risk of floods.

The Sierra snowpack has historically served as a natural reservoir, storing precipitation that falls as snow during the winter and releasing it slowly as it melts in the spring. With rising temperatures, more precipitation will instead fall as rain. The climate team predicts that the snowpack will be reduced by ten to forty percent by mid-century and from seventy to ninety percent by 2100, greatly reducing natural water storage.

An overlapping challenge will take place in the Delta, where even though overall flow in the Sacramento River is expected to decrease by about twenty percent by the 2050s, changing rainfall patterns will increase the risk of flooding. Severe storms are likely to damage already-compromised Delta levees and infrastructure.

Similarly, sea level is predicted to rise by 22 to 55 inches -- or even more -- by the year 2100. Rising sea levels will erode Delta levees and increase saltwater intrusion from San Francisco Bay, threatening the quality of water exports as well as of the Delta's water itself.

Yet as the human population continues to grow, especially in the drier southern region, where is the water going to come from to serve not only California's people but its agriculture, fish, and wildlife? And how can the state maintain control over its water supply in an era of climate change? While this gloomy conundrum has received attention lately, there is no agreement on what to do about it -- not strange, considering the state's always-fractious history of water management.

The solution proposed by California's Department of Water Resources, and supported by Governor Arnold Schwarzenegger, is to build more surface storage -- management-speak for more dams and reservoirs. During high winter flows, reservoirs store water that would otherwise be "lost" to the hungry sea. But water storage has always been a juggling act; managers need to keep reservoirs relatively empty during the wet season so that they have enough capacity to store water and reduce downstream flooding, while still keeping enough water available during the dry summer and fall. Managers are pretty good at guessing when to switch from releasing to storing water, but as the climate changes huge storms will become more frequent, leading to more flooding.

One of the three reservoirs the department has proposed building would be fifteen miles west of the Sacramento River, at a location called Sites in the Antelope Valley. Sites was part of the governor's nine-billion-dollar water bond proposal, which was rejected by the legislature last year. But building Sites, as well as its sister reservoirs, could still be put before voters as a ballot initiative.

The state is pitching the Sites reservoir as a tool to save fish and wildlife from global warming and to restore the Delta's delicate ecosystem. Migratory fish need higher flows, and maintaining a heavy water flow counteracts saltwater intrusion. According to Steve Roberts, manager of the department's surface storage investigations, the existing system is ill-equipped to address environmental needs. Sites would provide water managers with flexibility and "more knobs to turn" to meet both water supply and environmental obligations.