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Overpumping groundwater, worsening droughts and more rapid evaporation due to higher temperatures have caused a drastic decline in the amount of available freshwater, according to a new study.
“Continental drying” has redirected the planet’s total water to the oceans to such degree that it has now surpassed melting ice sheets as the biggest contributor to global sea level rise, the research found.
Losses of land-based water could have profound implications for access to safe drinking water and the ability to grow food in some of the world’s richest agricultural regions.
“We use a lot of water to grow food,” said Jay Famiglietti, a professor at Arizona State University’s School of Sustainability and one of the authors of the study. “If things don’t change, we’ll see impacts on our food security and just our general water availability.”
The findings “should be of paramount concern to the general public, to resource managers, and to decision-makers around the world,” the researchers wrote in the study, adding that the identified trends “send perhaps the direst message on the impact of climate change to date.”
“The continents are drying, freshwater availability is shrinking, and sea level rise is accelerating,” they wrote.
The study, published Friday in the journal Science Advances, assessed changes in terrestrial water sources, such as lakes, underground aquifers and moisture in soil, over the past two decades. The researchers found that several factors, including climate change, are disrupting Earth’s natural water cycle, upsetting how moisture circulates between the ground, oceans and atmosphere.
The researchers used data from a suite of four NASA satellites to analyze changes in terrestrial water storage over the past 22 years. The satellites were designed to track the movement of Earth’s water, including changes to the planet’s ice sheets, glaciers and underground reservoirs.
The researchers found, for instance, that parts of the world that are already dry have been rapidly getting drier since 2014. These drought-ridden regions increased by an area twice the size of California each year, Famiglietti said.
In several cases, drought-ridden hotspots expanded to create giant, interconnected “mega-drying” regions, according to the study. One such area covers parts of Central America, Mexico, California, the southwestern United States, the lower Colorado River basin and the southern High Plains.
“The key message here is that water is really a key driver of the changes we see both on land and in the ocean,” said Benjamin Hamlington, a research scientist in the Earth Sciences Section at NASA’s Jet Propulsion Laboratory who served on the science team for the NASA missions that produced the decades of data used in the new study.
The study found that every large land mass, except for Greenland and Antarctica, has experienced unprecedented drying since 2002.
Widespread continental drying is expected to have major consequences for people. Three quarters of the world’s population lives in countries where freshwater resources are being depleted, according to the researchers.
Meanwhile, rising seas threaten to creep up on coastal regions around the globe, making them less habitable and adding to the mounting pressures caused by extreme storms and floods. In the U.S., severe weather has helped trigger an insurance crisis in coastal cities that are prone to extreme weather events.
The link between sea-level rise and the loss of water locked up in the ground is a consequence of throwing the planet’s water cycle into chaos. Many of these changes, such as overpumping groundwater, are thought to be permanent — or, at the very least, irreversible for thousands or tens of thousands of years, said Alexander Simms, a professor in the Department of Earth Science at the University of California, Santa Barbara, who was not involved with the study.
“If you pull water off the continents, the only place it has to go is in the ocean,” he said. “Water goes in the atmosphere, then 88% of that water rains down on Earth and ends up in the ocean.”
Simms said the study was fascinating in its ability to estimate the global scale of these water losses, but he was skeptical of the claim that water loss from the continents has now surpassed ice sheet melt as the biggest contributor to sea level rise.
Still, Hamlington said the study shows how the movement of water around the planet has enormous ripple effects. It also suggests that the consequences could intensify in the future, if groundwater is further depleted, freshwater resources shrink and drought conditions worsen.
“This kind of tracking of terrestrial water storage is a critical piece of the puzzle,” he said. “If we can track that water, if we know where it’s going, we can improve our understanding of future drought, flooding and water resource availability over land.”
This article was originally published on NBCNews.com
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