Water investment needing to include flood preparation

The next huge natural catastrophe to strike California might not be an earthquake. New research suggests that a major flood could inundate large swaths of California in the next few decades. The last “200-year flood” was more than 150 years ago, and climate change is jacking up the odds of a repeat sooner rather than later. In order to prepare, state water officials must rethink whether big, costly dams really are the best investment of limited resources.

The peer-reviewed research, which appeared in the journal Nature Climate Change, predicts that California’s average annual rainfall will remain fairly stable in a warming world. The problem is in the annual fluctuations and potential for shorter more-intense wet seasons.

Right now, average annual precipitation in Sonoma County is about 31 inches. We could average that with 30 inches some years and 32 inches in others.

The models predict much greater variation. We could dip into prolonged droughts followed by a year of extreme rain such as the one that hit in the winter of 1861-62. That winter it rained for more than 40 days, with more than 100 inches falling on the western slopes of the Sierra Nevada. The Central Valley became a 300-mile long, 25-mile wide inland sea. Some of the valley’s farmlands and natural areas were under 20 feet of water.

It was catastrophic. People drowned and disappeared. Homes were destroyed. More than a million sheep, lambs and cattle died, ruining people’s livelihoods. In one of the more surreal moments, Gov. Leland Stanford arrived at his inauguration by rowboat on the streets of Sacramento. Shortly afterward, lawmakers moved the Capitol to San Francisco temporarily while the water slowly receded.

Now researchers warn that transitions between dangerously dry spells to dangerously wet could become more common. “Precipitation whiplash,” as they call it, isn’t a far-off thing that only our grandchildren need worry about. The new study predicts better than a 50 percent chance that an 1862like rainfall could hit in the next 40 years. And today there are far more people, buildings and investment in flood-prone areas.

California is not ready, but at least we’ve been warned. With luck, we have time to act.

In 2014, drought-stricken voters approved $2.6 billion in bond funds to improve the state’s water infrastructure. The California Water Commission, tasked with spending that money, is being lobbied hard to go with big-ticket projects. Two of them — a 10th dam on the San Joaquin River and the Sites Reservoir in the Sacramento Valley — could suck up most of the money. Big dams aren’t cheap.

Meanwhile, smaller, less-expensive proposals that deliver much greater bang for the buck languish. The water commission is supporting a handful of them, including groundwater recharging and recycling, but they are afterthoughts when these and other projects that spread flood resilience should be priorities.

The water commission will meet next week, beginning on Tuesday, to discuss appropriations of the bond money. It should consider how to prepare the state not just to fight drought with huge dams but also how it can begin to protect California from the next 1862 flood. That’s won’t please the big Central Valley growers who have been driving the conversation so far, but it’s the responsible forethought the state needs.