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This picture shows how much California is sinking

This picture from NASA's Earth Observatory shows how much land in California's Central Valley is sinking, due primarily to the drawing of groundwater during periods of drought.

Heavy rains have fallen on many parts of the state this winter, but the image above is a reminder of the lingering effects of drought, even in wetter times.

As the legend at the bottom of the picture suggests, the yellowest areas are those with the greatest degree of subsidence (the term for sinking land) and the bluest areas are those with the least.

As might be expected, the largest degree of subsidence occurred in southern California where the drought struck the hardest. In some places, the land sunk by nearly 30 feet.

California's Department of Water Resources commissioned NASA's Jet Propulsion Laboratory to collect and analyze satellite data during the state's most recent drought, resulting in an initial report in 2015, and subsequent updates. The most recent shows land continued to sink since 2015, at a rate of as much as 2 feet per year in the worst spots.

"The rates of San Joaquin Valley subsidence documented since 2014 by NASA are troubling and unsustainable," DWR Director William Croyle is quoted saying in a recent post from NASA Earth Observatory. "Subsidence has long plagued certain regions of California. But the current rates jeopardize infrastructure serving millions of people. Groundwater pumping now puts at risk the very system that brings water to the San Joaquin Valley. The situation is untenable."

One of the problems that stems from the sinking land is that it fills in the underground gaps where groundwater collects when rain occurs, reducing storage capacity.

NASA also notes that state and federal water agencies have spent an estimated $100 million on related repairs since the 1960s.

The state passed its first-ever regulations around the pumping of groundwater in 2014.