Continents have lost so much water since 2002 that they have surpassed ice sheets as the biggest contributor to global sea level rise, a new study reveals.
Almost 70% of this loss is due to unchecked groundwater extraction, which removes water from deep aquifers and eventually transfers it to the ocean, researchers found. Together with rising rates of evaporation due to climate change, this has caused rapidly drying “hotspots” to merge into four “mega-drying” regions, the scientists said.
“There’s very few places now that are not drying,” study co-author Jay Famiglietti, a professor in the School of Sustainability at Arizona State University, told Live Science. “I’ve been watching it for 20 years, and it’s just gotten worse, and worse, and worse.”
To measure continental drying, the researchers used data from satellites that respond to small mass changes on Earth. Gravitational pull drags the satellites down when an area gains water weight and releases them back to their initial orbit when water is lost. The resolution on the ground is about 15 miles (25 kilometers), which is enough to detect small changes on regional scales, Famiglietti said.
Drying hotspots are typically regions with big aquifers that humans have heavily exploited for decades, meaning they have high rates of water loss, Famiglietti said. These hotspots include places like the North China Plain, northwest India and California’s Central Valley, which have lost enormous amounts of water through human activities and evaporation. This water either enters rivers, which end up in the ocean, or rains out of the atmosphere over the ocean — ultimately making sea levels rise.
The new findings, published July 25 in the journal Science Advances, show that drying hotspots are rapidly expanding, and many of these areas are joining up. “South Asia is a great example,” Famiglietti said. “Around the Himalayas, there used to be four or five hotspots. Now it’s just all the way across.”
The study’s authors called these continent-size areas mega-drying regions. They identified three other such regions worldwide, all of which are in the Northern Hemisphere: one combining Alaska, northern Canada and northern Russia, another spanning Western Europe, and a third straddling southwestern North…
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