California Flooding Revealed in NASA Before and After Satellite Images

The scale of flooding across California in the wake of several intense atmospheric river storms has been captured by NASA satellites.

The images show California on January 15 before the major storms arrived, then again on February 4, after the first set of storms battered the state.

These early February storms hit one after the other in quick succession, bringing with them intensely strong winds and record-breaking rains. The storms were atmospheric rivers, which are long, thin weather systems containing immense volumes of water vapor that form over the tropics, releasing the water as rain and snow as they move over land.

Parts of Los Angeles County saw over 13 inches of rain across the four days before February 6, according to National Weather Service data, with over 7 inches on February 5 and 6 alone, saturating the ground and leading to flash flooding across the city. Usually, there is only about 3.64 inches of rain in LA across the entire month of February, with the city seeing only 14.25 inches yearly.

The satellite images show the degree of flooding across Mendocino County in Northern California, about 100 miles north of San Francisco. Higher water heights relative to sea level are shown as lighter shades in the images, revealing the extent of the flooding. Each pixel in the image represents an area of 330 feet by 330 feet.

The images were captured by the Surface Water and Ocean Topography (SWOT) mission, which is a collaboration between NASA and the French space agency, CNES (Centre National d'Études Spatiales).

SWOT has been measuring the levels of water across the entire globe since late 2022, allowing researchers to create an extremely detailed view of how the levels of the rivers and lakes around the world are changing. It measures these water levels using an instrument called the Ka-band Radar Interferometer, which uses two antennae 33 feet apart to bounce radar off water surfaces and measure their height.

"SWOT gives us information about flooding that we've never had before," Ben Hamlington, lead researcher for NASA's sea level change team at the agency's Jet Propulsion Laboratory in Southern California, said in a statement. "Data from the SWOT satellite, combined with other information, is filling in this picture."

In the weeks since the February 4 picture was taken, several more powerful atmospheric rivers have inundated California with wind and rain, causing widespread flooding and mudslides. This has led to San Diego, Los Angeles, and Riverside all exceeding a year's worth of rainfall since October, with Los Angeles seeing 18.2 inches, San Diego seeing 9.82 inches, and Riverside seeing 9.68 inches. These cities usually see 14 inches, 9.79 inches, and 9.37 inches of rainfall in a whole year on average, respectively.

"Ever wonder how much rain falls in your area each year? San Diego and Riverside have seen their annual average rainfall since the start of the water year on October 1st," the National Weather Service (NWS) office in San Diego posted on X, formerly Twitter, on Sunday.

Another storm is on its way to California later this week.

"Ready for more rain? Maybe not but precipitation is expected with a new Pacific storm Wednesday afternoon through Thursday," NWS San Diego said on X on Monday.

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