Farmers are facing a serious groundwater crisis in India as aquifers are dry.
Steve Elfers, Ian James

PALM SPRINGS, California – People are dramatically changing the water supply in many places around the world, say NASA scientists who have tracked regional changes via satellites.

The researchers analyzed 14 years of data from NASA's satellite Gravity Recovery and Climate Experiment Space Agency has christened GRACE. They studied areas of large increases or decreases in freshwater – including water stored in aquifers, ice, lakes, rivers, snow, and soil – to determine the most likely causes of these changes.

Changes in two-thirds of the 34 California-China hotspots could be related to climate change or human activity, such as excessive groundwater pumping for agriculture, according to their new study.

"The human fingerprint is the ever-changing abundance of fresh water, and we see it as a major overuse of groundwater, and we see it as a driver of climate change," said Jay Famiglietti, a co-author of research, the lead water scientist at Jet Propulsion NASA's Laboratory in Pasadena, California. "The study shows that humans have drastically changed the global waterscape in a very profound way."

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In 14 areas – more than 40% of the hotspots – the scientists associated the water in part or largely with human activity. These included groundwater shortages and drought in southern California, the southern Great Plains from Kansas to the Texas Panhandle, the northern Middle East, North Africa, southern Russia, Ukraine and Kazakhstan.

In eight of the regions, the trends reflected the suspected effects of climate change, according to the researchers:

• Loss of ice sheets in Greenland and the Antarctic
• Precipitation rises in the north -Eurasia and North America
• Retreat of Alaska Glaciers
• Melting Ice Fields in Patagonia at the southern tip of South America

They attributed changes in 12 regions to natural variability, including a progression from dry to dry wet in the northern Great Plains, a drought in eastern Brazil and wetter periods in the Amazon and tropical West Africa.

Many areas where researchers saw direct human impacts are agricultural regions that rely heavily on groundwater pumps, including North India, the North China Plain, and parts of Saudi Arabia.

In Africa, the Moroccan government has drilled deep wells to help a small group of farmers in the Souss-Massa region. The water flows from three wells into a tank and the farmers buy the water of a cooperative to irrigate their fields. (Photo: Steve Elfers / USA TODAY)

Other diversions have led to a decline in sea level for the Caspian Sea. The construction of the world's largest hydroelectric power station, the Three Gorges Dam on the Yangtze River in China and other reservoirs in China also has environmental implications.

"This is the first time GRACE's global trend map has been thoroughly analyzed this way," said Matthew Rodell, lead author and head of the Hydrological Sciences Laboratory at NASA's Goddard Space Flight Center in Greenbelt, Maryland get a global picture of how water storage is changing and what the different causes are. "19659008] Previous studies have used satellite data to study regional water changes, or they have used hydrological models to estimate global trends.

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The researchers said their study, which was published Wednesday in the journal Nature is the first that combines direct satellite measurements and other data sets to detect changes in freshwater all over the country Evaluate planets and analyze the causes. Research has enabled them to produce what they call the first satellite-based map of changes in the availability of freshwater worldwide.

Yoshihide Wada, a water scientist at the International Institute for Applied Systems Analysis in Laxenburg, Austria, was not The scientists involved in the study praised the research for the detailed presentation of the probable drivers of water trends.

"Water scarcity is becoming increasingly severe and we need to consider better water management practices in many intensively irrigated regions," Wada said. "In these regions, human impacts are expected to put much more pressure on freshwater resources than climate change."

This map shows changes in total freshwater from 2002 to 2016 as measured by NASA's Satellite Gravity Recovery and Climate Experiment. These include changes in aquifers, ice, lakes, rivers, snow and soils. (Photo: NASA, based on a study by Matthew Rodell et al., 2018)

The decline in freshwater was evident in many of the world's major food-producing regions from California and the American Southwest to India North China Plain, parts of the Middle East and South Russia.

"These are critical food-producing regions that rely on a resource that is dwindling," Rodell said. "And either they have to be more efficient in their water consumption, or eventually the food has to be." grown elsewhere. "

The scientists estimated the water losses and profits in gigatonnes per year, each gigaton of water being one billion tons, enough to fill 400,000 Olympic swimming pools.

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For the Sense of Scale Das the largest reservoir in the United States, Lake Mead, holds about 32 gigatonnes when it is full, and in the 14 years of satellite measurements, almost all regions lost or gained so much that eleven of the regions lost or gained 10 times or so more.

"The numbers are huge. "In the Greenland region, where the ice is melting rapidly as the planet warms, researchers estimate water losses at a rate of 279 gigatonnes per year – a figure that equals eight full-blown meadows, oceans, and sea-level rise In the Antarctic, they estimated losses of 128 gigatons of ice per year.

A NASA photo from November 2016 shows one Cleavage in the Larsen C Ice Shelf of the Antarctic Peninsula. [Photo: John Sonntag, AP]

The results show that Southern California, including the farmlands in the San Joaquin Valley, has more than 4 gigatons of water per year between 2002 and 2016 lost – a time in which breeders relied heavily on groundwater pumps during the most severe drought in modern state history.

The pressure from d Agriculture also led to a decline in groundwater in Saudi Arabia, which lost 6.1 gigatons of water per year at a time when irrigated farmland in the desert was expanding.

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The two GRACE satellites were launched in 2002 as a joint mission of NASA and the German Space Agency. The satellites monitored changes in Earth's gravity field, serving as a "scale in the sky" and measuring shifts in total water levels both above and below ground.

The satellites generated data until last year. Then both spacecraft reentered the atmosphere and burned over the oceans, one in December and the other in March.

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► March 2017: Environmental hopes cloud a year after Florida's Fish Apocalypse [19659008] The next generation of twin satellites named GRACE Follow-On is scheduled to enter California orbit on Tuesday.

"This map quantifies the pace of change – we can see and quantify the pace of change – it happens quickly," said Famiglietti, recently named director of the University of Saskatchewan's Global Institute for Water Security. "So there are no excuses when it comes to planning water resources."

Follow Ian James on Twitter: @TDSIanJames

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