Tracking California’s water supplies

The American Southwest recently experienced its driest period in 1,200 years. Storms in the winter of 2023 eased some of California’s extreme drought conditions, but officials stress that conservation should remain a way of life.

This page tracks hydrological conditions, precipitation, the Sierra snowpack and the largest reservoirs serving the state.

California’s worsening droughts

California naturally cycles between wet periods and droughts. But scientists have found that globally climate change is intensifying the water cycle and bringing more extreme droughts, as well as more extreme bouts of wet weather.

The graphic below shows the intensity and duration of droughts and wet periods since the 1980s. Over the last decade, the state has endured more frequent and severe dry periods punctuated by fewer wet years.

How much rain and snow has fallen in California?

Precipitation is tracked the across the “water year,” beginning Oct. 1 and ending Sept. 30.

As of May 2, the state has received 22.5 inches of precipitation, or 105% of the average for this date.

California typically sees most of its rain and snow during the first half of the water year, which is followed by the warmer and drier spring and summer. The graphic below shows daily precipitation totals since 2000 for the state and its major drainage basins, or hydrologic regions.

What role does the snowpack play in California’s water supply?

The Sierra Nevada snowpack serves as the state’s natural water storage system. In “normal” years, the snowpack accumulates in the winter months then melts gradually through the spring, feeding rivers and refilling reservoirs throughout the state.

The historic snowpack of 2023 eased drought conditions in most of the state.

How much water does California have stored in reservoirs?

California has the ability to store nearly 40 million acre feet of water behind dams around the state. The state Department of Water Resources reports a regular accounting of the water levels at 154 reservoirs representing the vast majority of the state’s water storage capacity.

As of May 1, state reservoirs stand at about 86% capacity. That’s above the 30-year average of 76% for the month of May.

Large Northern California reservoirs supply Southern California with much of its water. Below are the current levels for some of the major reservoirs, in order of total capacity.

Lake Mead and Lake Powell, the country’s largest reservoirs, lie beyond state borders but hold a significant amount of Colorado River water that is used by Southern California. Here’s where these reservoirs stand as of May 1.

How dry is California?

The drought in California and the American West has been worsened by rising temperatures caused by climate change. Scientists in 2022 found that the region as a whole, from Montana to California to northern Mexico, experienced the driest 22-year period in more than 1,200 years.

Since 2000, the U.S West. has grown warmer and drier. Data from the U.S. Drought Monitor shows that the region has plunged deeper into extreme drought over the past several years. Scientists have increasingly said the West is experiencing “aridification” driven by human-caused climate change, and they have called for the region to prepare for drier conditions in the long term as temperatures continue to rise.

Compared with 2022, conditions in the U.S. have improved. About 37% of the country is at least abnormally dry, according to the drought monitor.