Disasters More Likely
Ironically, atmospheric rivers that set up over California are not all bad. The smaller ones that arise annually are important sources of water. By analyzing the amount of rain and snow that atmospheric rivers brought to the U.S. West Coast in recent decades, along with records about long-term precipitation, snowpack and stream flow, researchers have found that between 1950 and 2010, atmospheric rivers supplied 30 to 50 percent of California’s water—in the span of only 10 days each year. They are finding similar proportions along the rest of the West Coast. In the same time period, however, the storms also caused more than 80 percent of flooding in California rivers and 81 percent of the 128 most well-documented levee breaks in California’s Central Valley.