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    • By NASA
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      Despite some years with significant snowfalls, long-term drought conditions in the Great Basin region of Nevada, California, Arizona, and Utah, along with increasing water demands, have strained water reserves in the western U.S. As a result, inland bodies of water, including the Great Salt Lake pictured here, have shrunk dramatically, exposing lakebeds that may release toxic dust when dried.Dorothy Hall/University of Maryland Record snowfall in recent years has not been enough to offset long-term drying conditions and increasing groundwater demands in the U.S. Southwest, according to a new analysis of NASA satellite data.
      Declining water levels in the Great Salt Lake and Lake Mead have been testaments to a megadrought afflicting western North America since 2000. But surface water only accounts for a fraction of the Great Basin watershed that covers most of Nevada and large portions of California, Utah, and Oregon. Far more of the region’s water is underground. That has historically made it difficult to track the impact of droughts on the overall water content of the Great Basin.
      A new look at 20 years of data from the Gravity Recovery and Climate Experiment (GRACE) series of satellites shows that the decline in groundwater in the Great Basin far exceeds stark surface water losses. Over about the past two decades, the underground water supply in the basin has fallen by 16.5 cubic miles (68.7 cubic kilometers). That’s roughly two-thirds as much water as the entire state of California uses in a year and about six times the total volume of water that was left in Lake Mead, the nation’s largest reservoir, at the end of 2023.
      While new maps show a seasonal rise in water each spring due to melting snow from higher elevations, University of Maryland earth scientist Dorothy Hall said occasional snowy winters are unlikely to stop the dramatic water level decline that’s been underway in the U.S. Southwest.
      The finding came about as Hall and colleagues studied the contribution of annual snowmelt to Great Basin water levels. “In years like the 2022-23 winter, I expected that the record amount of snowfall would really help to replenish the groundwater supply,” Hall said. “But overall, the decline continued.” The research was published in March 2024 in the journal Geophysical Research Letters.
      “A major reason for the decline is the upstream water diversion for agriculture and households,” Hall said. Populations in the states that rely on Great Basin water supplies have grown by 6% to 18% since 2010, according to the U.S. Census Bureau. “As the population increases, so does water use.”
      Runoff, increased evaporation, and water needs of plants suffering hot, dry conditions in the region are amplifying the problem. “With the ongoing threat of drought,” Hall said, “farmers downstream often can’t get enough water.”
      Gravity measurements from the GRACE series of satellites show that the decline in water levels in the Great Basin region from April 2002 to September 2023 has most severely affected portions of southern California (indicated in red).D.K. Hall et al./Geophysical Research Letters 2024 While measurements of the water table in the Great Basin — including the depths required to connect wells to depleted aquifers — have hinted at declining groundwater, data from the joint German DLR-NASA GRACE missions provide a clearer picture of the total loss of water supply in the region. The original GRACE satellites, which flew from March 2002 to October 2017, and the successor GRACE–Follow On (GRACE–FO) satellites, which launched in May 2018 and are still active, track changes in Earth’s gravity due primarily to shifting water mass.
      GRACE-based maps of fluctuating water levels have improved recently as the team has learned to parse more and finer details from the dataset. “Improved spatial resolution helped in this study to distinguish the location of the mass trends in the Western U.S. roughly ten times better than prior analyses,” said Bryant Loomis, who leads GRACE data analysis at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
      The diminishing water supplies of the U.S. Southwest could have consequences for both humans and wildlife, Hall said. In addition to affecting municipal water supplies and limiting agricultural irrigation, “It exposes the lake beds, which often harbor toxic minerals from agricultural runoff, waste, and anything else that ends up in the lakes.”
      In Utah, a century of industrial chemicals accumulated in the Great Salt Lake, along with airborne pollutants from present-day mining and oil refinement, have settled in the water. The result is a hazardous muck that is uncovered and dried as the lake shrinks. Dust blown from dry lake beds, in turn, exacerbates air pollution in the region. Meanwhile, shrinking lakes are putting a strain on bird populations that rely on the lakes as stopovers during migration.
      According to the new findings, Hall said, “The ultimate solution will have to include wiser water management.”
      By James R. Riordon
      NASA’s Goddard Space Flight Center, Greenbelt, Md.
      Facebook logo @NASAEarth @NASAEarth Instagram logo @NASAEarth Share
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      Last Updated Jun 17, 2024 EditorRob GarnerContactJames R. Riordonjames.r.riordon@nasa.govLocationGoddard Space Flight Center Related Terms
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      Earth’s polar regions radiates much of the heat initially absorbed at the tropics out to space, mostly in the form of far-infrared radiation. Clouds in the Arctic — like these seen over a Greenland glacier — and Antarctic can trap far-infrared radiation on Earth, increasing global temperatures.NASA/GSFC/Michael Studinger Information from the PREFIRE mission will illuminate how clouds and water vapor in the Arctic and Antarctic influence the amount of heat the poles radiate into space.
      A pair of new shoebox-size NASA satellites will help unravel an atmospheric mystery that’s bedeviled scientists for years: how the behavior of clouds and water vapor at Earth’s polar regions affects our planet’s climate.
      The first CubeSat in NASA’s Polar Radiant Energy in the Far-InfraRed Experiment (PREFIRE) mission launched from New Zealand on Saturday, May 25. The second PREFIRE CubeSat is targeted to lift off on Saturday, June 1, with a launch window opening at 3 p.m. NZST (11 p.m. EDT, Friday, May 31).
      The mission will measure the amount of heat Earth emits into space from the two coldest, most remote regions on the planet. Data from PREFIRE will improve computer models that researchers use to predict how Earth’s ice, seas, and weather will change in a warming world.
      This video gives an overview of the PREFIRE mission, which aims to improve global climate change predictions by expanding scientists’ understanding of heat radiated from Earth at the polar regions. NASA/JPL-Caltech Earth absorbs a lot of the Sun’s energy in the tropics, and weather and ocean currents transport that heat toward the poles (which receive much less sunlight). Ice, snow, and clouds, among other parts of the polar environment, emit some of that heat into space, much of it in the form of far-infrared radiation. The difference between the amount of heat Earth absorbs at the tropics and that radiated out from the Arctic and Antarctic is a key influence on the planet’s temperature, helping to drive dynamic systems of climate and weather.
      But far-infrared emissions at the poles have never been systematically measured. This is where PREFIRE comes in. The mission will help researchers gain a clearer understanding of when and where Earth’s polar regions emit far-infrared radiation to space, as well as how atmospheric water vapor and clouds influence the amount that escapes.
      One of the two shoebox-size CubeSats that make up NASA’s PREFIRE mission sits on a table at Blue Canyon Technologies. The company built the satellite bus and integrated the JPL-provided thermal infrared spectrometer instrument.NASA/JPL-Caltech Clouds and water vapor can trap far-infrared radiation on Earth, thereby increasing global temperatures — part of the greenhouse effect.
      “It’s critical that we get the effects of clouds right if we want to accurately model Earth’s climate,” said Tristan L’Ecuyer, a professor at the University of Wisconsin-Madison and PREFIRE’s principal investigator.
      Clouds in Climate Modeling
      Clouds and water vapor at Earth’s poles act like windows on a summer day: A clear, relatively dry day in the Arctic is like opening a window to let heat out of a stuffy room. A cloudy, relatively humid day traps heat like a closed window.
      The types of clouds — and the altitude at which they form — influence how much heat the polar atmosphere retains. Like a tinted window, low-altitude clouds, composed mainly of water droplets, tend to have a cooling effect. High-altitude clouds, made mainly of ice particles, more readily absorb heat, generating a warming effect. Because clouds at mid-altitudes can have varying water-droplet and ice-particle contents, they can have either a warming or cooling effect.
      But clouds are notoriously difficult to study: They’re made up of microscopic particles that can move and change in a matter of seconds to hours. When it rains or snows, there’s a great reshuffling of water and energy that can alter the character of clouds entirely. These ever-changing factors complicate the task of realistically capturing cloud behavior in climate models, which try to project global climate scenarios.
      Inconsistencies in how various climate models represent clouds can mean the difference between predicting 5 or 10 degrees Fahrenheit (3 or 6 degrees Celsius) of warming. The PREFIRE mission aims to reduce that uncertainty.
      The thermal infrared spectrometer on each spacecraft will make crucial measurements of wavelengths of light in the far-infrared range. The instruments will be able to detect clouds largely invisible to other types of optical instruments. And PREFIRE’s instruments will be sensitive enough to detect the approximate size of particles to distinguish between liquid droplets and ice particles.
      “PREFIRE will give us a new set of eyes on clouds,” said Brian Kahn, an atmospheric scientist at NASA’s Jet Propulsion Laboratory and a member of the PREFIRE science team. “We’re not quite sure what we’re going to see, and that’s really exciting.”
      More About the Mission
      PREFIRE was jointly developed by NASA and the University of Wisconsin-Madison. A division of Caltech in Pasadena, California, JPL manages the mission for NASA’s Science Mission Directorate and provided the spectrometers. Blue Canyon Technologies built the CubeSats, and the University of Wisconsin-Madison will process and analyze the data the instruments collect.
      NASA’s Launch Services Program selected Rocket Lab to launch both spacecraft as part of the agency’s Venture-class Acquisition of Dedicated and Rideshare (VADR) contract. CubeSats like PREFIRE serve as an ideal platform for technical and architecture innovation, contributing to NASA’s science research and technology development.
      To learn more about PREFIRE, visit:
      https://science.nasa.gov/mission/prefire/
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      Jet Propulsion Laboratory, Pasadena, Calif.
      818-354-0307 / 626-379-6874
      jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov
      2024-076
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      Last Updated May 30, 2024 Related Terms
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