If you've ever shopped around for securities or mutual funds, you've heard the caveat that past results are no guarantee of future performance. The same warning apparently applies to California's water system.

A report released by the White House this week makes clear that climate change is very likely to alter precipitation patterns. Essentially, the mountains will get more rain and less snow, and arid areas will experience longer droughts. Much of California's water system — the federal Central Valley Project, the State Water Project and the Colorado River system — is predicated on capturing and redirecting snowmelt during the dry months of late spring, summer and early fall. We need to rethink this system, according to "The Scientific Assessment of the Effects of Global Change on the United States."

"Although U.S. water management practices are generally quite advanced, particularly in the West, the reliance on past conditions as the foundation for current and future planning and practices will no longer be tenable as climate change and variability increasingly create conditions that are well outside of historical parameters, eroding predictability," the report states.

The report continues: "Across North America, vulnerability to extended drought is increasing as population growth and economic development create more demands from agricultural, municipal and industrial uses, resulting in frequent over-allocation of water resources. Examples of vulnerable U.S. regions include: the heavily used water systems of the West that rely on capturing snowmelt runoff, such as the Colombia and Colorado River systems; portions of California …"

The 271-page report — which the Bush Administration released only under court order — does not present new science. Rather, it is a comprehensive summary of federal and independent research concerning human-caused global climate change.

Give credit to the California Department of Water Resources, which — as we reported in 2003 — has been grappling with the implications of climate change for years. A climate change technical advisory committee is assisting with an ongoing update of the California Water Plan.

The White House report says that predicting climate change's impact on particular cities or regions is difficult because of climate variability. Still, the report is packed with findings of particular relevance to California. Among those findings are these:

• Sea level is expected to rise between 7 and 23 inches by the end of the this century — and could rise even more depending on ice melt in Greenland and Antarctica. This higher sea level combined with expected larger storm surges will increase coastal erosion and cause damage farther inland.

• During the last three decades, fire season in the West has lengthened, and burn duration has increased, partly because of climate change-caused insect outbreaks and tree mortality. "These trends are very likely to continue."

• "Many plants and animals in arid ecosystems are near their physiological limits for tolerating temperature and water stress, and even slight changes in stress will have significant consequences." Riparian ecosystems in arid areas are particularly vulnerable, as are "iconic megaflora, such as saguaro cacti and Joshua trees" that are not adapted to cycles of fire. This finding makes one wonder about the long-range habitat conservation plans prepared for San Diego County, western Riverside County, the Coachella Valley and the Mojave Desert.

• Coldwater fisheries will suffer in the southern portions of ranges, a finding that raises questions about the survival of salmon and steelhead in California.  

• Water quality will diminish because of higher surface water temperatures, intrusion of saltwater into groundwater aquifers, and the introduction of more sediment, nutrients, pathogens and toxics caused by increased intense rainstorms. "These water quality changes could impose enormous costs on water treatment infrastructure."

• Population growth is shifting toward coastal regions most vulnerable to the effects of climate change. Hello L.A. and San Diego.

• Flooding and landslides are "very likely" to interrupt road, rail and sea transportation systems. "The crucial connectivity of the transportation system means that the services of the network can be threatened even if small segments are wiped out."

The good news? Agricultural growing seasons should continue to lengthen, demand for wintertime heating will decrease, and wintertime road maintenance should be less of a concern. But those limited advantages or overwhelmed by the negatives.

- Paul Shigley