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No one loves a scold or a doomsayer, especially when the news is good. Still, some words of caution are in order. First, it’s important to remember that “drought” is defined not merely by whether the rain falls but by how much water is available for human needs and for keeping the natural environment healthy. The entire state is still suffering at least “moderate drought,” as calculated by the U.S. Drought Monitor, and in more than 90% of California the drought remains “extreme.” Much of the land is desiccated, and groundwater supplies are dangerously overtapped. Many more storms will be needed to make up for years with little rain or snow. Will we get those storms? We can hope. A wet December does not guarantee a wet January or February. It generally takes a season of powerful storms, known as atmospheric rivers, lining up as if on a conveyor belt, blasting ribbons of moisture over the region, to constitute a “drought buster.” Nor does a full Sierra snowpack now guarantee steadily melting spring and summer snow, as it once did. A warmer climate means snow often melts earlier in the year, and more rapidly, than it did during most years in the 20th century. California water experts predict that wet winters are as likely to cause flooding as they are to fill reservoirs at a manageable pace. This isn’t entirely new. California has long been a place of weather extremes. Flooding in 1861 (following, in California fashion, 20 years of drought) submerged the Capitol in Sacramento and lawmakers had to flee. Much of the San Joaquin Valley was inundated and became a 300-mile-long inland sea. Other years have seen regional flooding, as when a pair of storms in March 1938 caused the Los Angeles River to overflow its banks and flooding across the basin resulted in more than 100 deaths.
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