A Newsletter about California Water, Land, and People


Five Facts

While California's water system is complex in its details, some basic facts about the system and its history can guide you through its complexities to attain a basic understanding of California geography.

First, more than 70 percent of California's annual runoff (water entering and flowing in rivers from rain and snowfall) originates north of Sacramento.

Second, about 75 percent of the state's urban and agricultural demand for water occurs south of Sacramento.

Third, on average, 75 percent of California's average rainfall of 23 inches falls between the months of November and March. Half of it falls between December and February.

Delta channels, 1995. Photo courtesy of the
California Department of Water Resources.

Fourth, because a few storms occurring (or not occurring) during the state's rainy season can determine whether there is enough water for everyone in the state, Californians developed their water system to guard against both extreme drought and extreme flooding.

Fifth, most rivers of the Central Valley drain to the Delta formed where the Sacramento and San Joaquin rivers flow together near Stockton. These two rivers then flow through the Carquinez Straits at Vallejo, into San Francisco Bay, and out through the Golden Gate to the Pacific Ocean.

These five facts shape nearly everything that Californians have done, and will continue to do, to control and use water for farming or in cities.

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