What causes California droughts?
KR: California droughts are winter droughts, because there’s only one main precipitation season. During drought winters, storms that approach the West Coast often head north to Washington, Oregon, and Canada, or else they split and a piece goes north, another piece goes south. They don’t slam directly into the Sierra Nevada. In drought winters a lot of storms that come in do not reach the Sierra, but rather dive down to the south along the coast, to about the latitude of Los Angeles or so, and then head east—taking an unusual trajectory. The Sierra Nevada Mountain Range helps cause its own precipitation since it’s elevated and air has to go up over it—rising up those long slopes. Like a ramp, it starts at sea level at Sacramento, rising up the entire way, losing its moisture. This provides a more effective process for removing moisture than if the elevation were the same all the way. The presence of the mountains greatly accentuates precipitation, especially over the Sierra and to a le
