Friday, November 30, 2012

Tracing California’s Largest Floods

Is the pattern of flooding in California in recent years an abberation, or was the relative absence of flooding there during most of the 20th century just good luck? Soil studies and other historical evidence is suggesting the latter. A Scientific American story released on the web today, “Megastorms Could Drown Massive Portions of California,” talks about California‘s worst flood:

The intense rainstorms sweeping in from the Pacific Ocean began to pound central California on Christmas Eve in 1861 and continued virtually unabated for 43 days. The deluges quickly transformed rivers running down from the Sierra Nevada mountains along the state’s eastern border into raging torrents that swept away entire communities and mining settlements. The rivers and rains poured into the state’s vast Central Valley, turning it into an inland sea 300 miles long and 20 miles wide. Thousands of people died, and one quarter of the state’s estimated 800,000 cattle drowned. Downtown Sacramento was submerged under 10 feet of brown water filled with debris from countless mudslides on the region’s steep slopes. California’s legislature, unable to function, moved to San Francisco until Sacramento dried out—six months later. By then, the state was bankrupt.

Intense flood events seem to have hit California about 200 years, the story says, and could become more frequent with changes in climate. The weather events involved can’t be anticipated much more than a week in advance (though meteorologists are working on it), and such a flood now would be a disaster the state is in no way prepared for. Even without a flood the state government is in serious financial distress with little flexibility to respond to even routine problems.

Flooding is on people’s minds in the northern half of California this week with minor flooding occurring across a wide area today.