Impact of California’s Rainy Season on Water Supply

California’s winter rainy season has finally kicked into high gear after a dry start, with a series of deluges bringing much-needed precipitation to the state. The downpours began in December, leading to flash floods in various regions, including coastal Ventura County, Santa Barbara, San Diego, and Northern California. The recent storms have not only prevented a return to the drought that has plagued California for the past decade but have also resulted in an abundance of rainfall, with some areas even experiencing rare occurrences such as a sizable lake in Death Valley National Park.

Despite the historic levels of rainfall in Southern California, the state as a whole is still uncertain if it will be considered a very wet year. Northern California, in particular, is slowly approaching its annual average, with about a month and a half left in the wet season. While the Sierra Nevada snowpack, a crucial water source for California, has shown improvement from its initial slow start, it is still below normal levels for this time of year.

The Department of Water Resources reported that the snowpack’s water content is currently at 86% of normal levels to date and 69% of the April 1 average, which is when it typically reaches its peak. Last year, the snowpack was at an impressive 200% of its average content due to repeated atmospheric rivers that ended California’s driest three-year period on record.

Despite the delayed start to the rainy season, major reservoirs in California have maintained above-average water levels, thanks to runoff from last year’s record snowpack. Some reservoirs have been releasing water to accommodate incoming storm runoff and maintain flood control measures. The State Water Project is forecasting a 15% allocation of requested supplies for public water agencies, up from the initial 10% allocation in December, with the possibility of further revisions in mid-March.

Lake Oroville, the largest reservoir in the State Water Project, is currently at 134% of its average level to date. However, the Northern California headwaters of the State Water Project have experienced below-average precipitation in recent months. Federal authorities also announced a 15% allocation of requested water supplies for contractors of the Central Valley Project, a federally managed system that serves major farming districts. This allocation is subject to change with the arrival of more storms in the coming weeks.

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