Study: NASA satellites show areas growing drier, wetter

Luke Skywalker · Feb 17, 2016

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Fields of grain sorghum, also known as milo, surround grain silos in southwestern Kansas. The southern High Plains is one of the regions where NASA satellite measurements have shown losses of water during the past decade.(Photo: Ian James/The Desert Sun)

PALM SPRINGS, Calif. —*By studying more than a decade of measurements recorded by NASA satellites, scientists have documented a striking pattern in places around the world: many wet regions have grown wetter, while a number of dry regions have grown drier.
Researchers examined data*from NASA satellites between 2002 and 2014 and found areas that have become wetter included the upper Missouri River basin, the northern Amazon and parts of Africa, as well as other parts of the tropics. Areas throughout the mid-latitudes became drier: in the Middle East and North Africa, parts of India and China, and across*much of the southern and western United States, where drought-plagued California and the southern High Plains stood out for especially large losses of water.
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Those findings were part of a study that for the first time quantified how years of wet weather in parts of the world have left more water in lakes, soils and aquifers —*enough to have an effect on the rate of global sea-level rise. The research, published last week in the journal*Science, will likely lead to adjustments in calculations of contributions to sea-level rise in upcoming reports of the Intergovernmental Panel on Climate Change (IPCC).

This map shows trends in total land water storage, as measured by NASA's GRACE satellites, between April 2002 to November 2014. The map, which was published in the journal Science, shows regions that grew wetter in blue and regions that grew drier in red. The map excludes glaciers and ice sheets.*(Photo: Source: J.T. Reager and Jay Famiglietti, NASA Jet Propulsion Laboratory)

The study, led by researchers at NASA's Jet Propulsion Laboratory and University of California, Irvine,*also describes the trend of some areas growing wetter and others growing drier, illustrating those changes in patches of red and blue on a global map.
The data come from the twin satellites of the GRACE mission, which stands for Gravity Recovery and Climate Experiment. Since 2002, the satellites have been measuring shifts in the total amounts of water aboveground and underground, enabling scientists to track large-scale shifts.
“This concept of wet-get-wetter, dry-get-drier —*they call it the rich-get-richer mechanism —*has already been proposed as something that might happen under human-driven climate change. And we’re seeing something that’s consistent with that,” said*lead author J.T. Reager, a hydrologist at the Jet Propulsion Laboratory*in Pasadena. He stressed that the researchers can’t say whether or to what extent the shifts may be related to global warming —*versus natural variations in climate —*in part because 12 years is too short of a period to draw such conclusions.
The study’s findings add to previous research showing that many of the world’s large aquifers, including those in major food-producing regions, have been rapidly declining.
“The implications of our study for the redistribution of water availability are staggering and point to an emerging class of 'haves' and 'have nots,'” said co-author Jay Famiglietti, senior water scientist at the Jet Propulsion Laboratory and a professor at the University of California, Irvine. “When combined with our previous work on groundwater depletion, we are*revealing a global disaster in the making, yet we are seeing very little coordinated response."
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Famiglietti has called for better monitoring and exploration of groundwater and efforts to make more efficient use of water in agriculture. He has also suggested creating a coordinated global discussion through a body that would parallel the IPCC and focus on water issues.
Arid regions tend to depend more on groundwater, and aquifers have been severely depleted in some of the same regions that the satellite data show have become drier.

In this 2014 photo, the Coachella branch of the All-American Canal passes through the desert in Mecca, California.*(Photo: Richard Lui/The Desert Sun)

“It’s difficult to separate what’s happening naturally, what’s climate-driven and what’s human-driven,” Famiglietti said. But where it’s grown drier, in many cases people have been relying more on groundwater. “It’s raining even less, so the groundwater will get replenished even less. So that’s what we call a positive feedback.”
Famiglietti pointed out that the changes measured since 2002 are in line with projections of shifts in rainfall in IPCC climate models.
The research provides a new and useful global-scale view of changes in water supplies, said Michael Campana, a professor of hydrogeology at Oregon State University who was not involved in the study.
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“I think it can help people look at areas that didn’t have a lot of data,” Campana said. “Someone can look at that and say, ‘Hey, we better watch out for this area.’”
That could involve focusing more resources on a certain area, he said, or pointing to potential “hot spots” where conflicts over water might erupt. The research drawn from satellite data, Campana said, “really shows some of the challenges that we have facing us and gives us some tools that we can use to deal with them.”
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In another study published this month, scientists at the National Center for Atmospheric Research examined data for the southwestern U.S. and found the types of weather patterns that bring rainfall to the region have become rarer.
The researchers analyzed 35 years of weather data for the*study, which was published in the journal*Geophysical Research Letters. They noted that some climate model simulations have projected that as the climate grows warmer, it will make the Southwest drier. The scientists cautioned, however, that linking those projections to changes over the past 35 years is difficult, and they are continuing to study that potential connection.
The scientists said*their results*show that an average year in the Southwest has grown drier than in the past, and that has made droughts more intense.
Famiglietti said the findings about the Southwest fit with the global changes shown in the GRACE satellite data. Overall, he said, “it’s a pretty dire picture.”
In their global study, the team led by Reager and Famiglietti —*which also included scientists from the University of Bonn in Germany and National Taiwan University —*found that many dry areas throughout the mid-latitudes have largely become drier since 2002. There were some areas that don’t fit cleanly into the larger wetter/drier pattern, including in parts of Africa and Asia. But in many places, the tropics grew wetter, as did northern latitudes across North America, Europe and Asia.
The scientists call it “a distinct pattern of mid-latitude drying, which is more pronounced in the northern hemisphere, and of high- and low-latitude wetting.”

Floodwaters cover Interstate 44 in Valley Park, Missouri, on Dec. 30, 2015. The upper Missouri River basin is among the regions that NASA satellites have shown growing wetter since 2002.*(Photo: Jeff Roberson, AP)

They also spotted variations including La Niña-driven storms that brought heavy rains to parts of northern Australia after years of drought.
The researchers found that during years of wet weather, storms sweeping in from the ocean can dump such vast quantities of water on land that the phenomenon can alter the rate at which the world’s oceans are rising. Their findings show that while glaciers and ice sheets continue to melt around the world due to human-caused climate change, those periods of wet weather also have an effect. That is likely to lead to changes in how scientists break down their “budgeting” of contributions to global sea-level rise.
Looking at the global average of the world’s continents as whole, Reager said, there has been an increase in rainfall over land during the past 12 years.

A farmer rides his water buffalo in floodwaters on Oct. 19, 2015, after Typhoon Koppu unleashed heavy rains in Barangay Camanutan in the Philippines.*(Photo: AFP/Getty Images)

He and his colleagues calculated that the increase in the quantities of water stored on land —*in lakes, soil and aquifers*—*has slowed the apparent pace of sea level rise by more than 20%*from 2002 to 2014. That has occurred while the melting of ice sheets and glaciers has accelerated, and while groundwater pumping has contributed to the problem by sending more water flowing to the oceans.
The researchers found that if it weren’t for the years of wetter weather in parts of the world during the 12-year period, sea*level would have risen faster —*and the rise could accelerate in the future when weather fluctuates in a drier direction on the global scale.
“That just tells you how powerful these kinds of weather fluctuations can be in terms of moving water from the ocean to the land,” Reager said. “It kind of demonstrates the power of that natural variability in the water cycle.”
Follow*Ian James on Twitter: @TDSIanJames

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Study: NASA satellites show areas growing drier, wetter

Luke Skywalker

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