Satellites reveal gains in California water
Satellites reveal gains in California water
Credit: NASA

Data from the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellite mission, a joint effort between NASA and the German Research Centre for Geosciences (GFZ), shows that California has recently experienced its largest year-over-year water gains in twenty years. The water deficit that the state experienced throughout dry spells over the last decade, including the three driest years on record in California, was partially alleviated by the abundance of climatic rivers that flowed this past winter.

Central Valley (yellow) is a vast pool that represents much of the state. All surface and subsurface water sources, including as lakes, rivers, soil, snowpack, and aquifers, are accounted for in GRACE-FO observations. The amount of water in the “swimming pool” was increased by around 20 inches (about 500 millimetres) due to rainfall between October 2022 and March 2023. Since the first GRACE goal began measuring water storage via satellite in 2002, this is roughly twice as much water as is typically gained over the winter.

The above maps show the increase of water from October 2022 to March 2023. Where precipitation was above average (compared to 2004–2010), the map will be blue, and where it was below average, the map will be red. The monthly fluctuations in water storage for the area highlighted in yellow on the maps are programmed by the yellow line in the table below.

It may take years for aquifers, underground reservoirs of fresh water used for irrigation and other purposes, to fully recharge while surface water basins are filling. According to Felix Landerer, GRACE-FO task researcher at NASA’s Jet Propulsion Laboratory, “one excellent winter season of rain and snow will not offset years of severe dry spell and substantial groundwater usage.” After the snowfall melts and water levels in the state’s lakes, rivers, and tanks begin to decline due to the dry weather, the GRACE-FO group will continue to monitor the progress of California’s water storage throughout the summer.

Satellites reveal gains in California water
2002 – 2023. Credit: NASA

October 2002 – March 2023MPEG. Credit: NASA

The unique method of observation employed by both GRACE missions made the observations possible. The mass of the Earth’s near-surface region is constantly changing as a result of the motion of water in the form of ocean currents, pouring rain, flowing groundwater, ice, and so on. Without GRACE-FO, scientists would only be able to make rough estimates of how much water has changed in a given region.

The GRACE-FO mission, like its forerunner, consists of two identical satellites in a tailed formation. The distance between the satellites grows as the lead satellite flies over a region with greater mass, such as an area with more water than another region. The spacecraft’s microwave and laser instruments precisely measure the slight differences in separation between them, revealing data on the water’s overall density.

Gains in water availability in California as seen by satellites (2023, June 18) retrieved 2019-06-19 from

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