farming, and commercial uses. “In some places, it’s unclear how much groundwater exists, and it’s unclear how fast it’s going to run out,” Swenson said. In highly water-stressed areas, 40 to 100 percent of the local water supply is withdrawn by businesses, farmers, residents and other consumers every year. As valuable as GRACE’s groundwater data is, it has a crucial gap: it cannot show the total volume of groundwater available in the aquifers it tracks, only the rate of decline. This project, called the Gravity Recovery and Climate Experiment (GRACE), measures changes in the Earth’s gravity. 2006. Specifically, this project focuses on 1. This model uses data from instruments on a new pair of satellites that measures changes in the Earth’s gravity. These data and analyses are critically important, raising awareness about an underreported issue and looming crisis, and allowing governments, development organizations, companies and researchers around the world to concentrate their groundwater work on the worst-suffering areas. Swenson said, “The GRACE data provide a broad-scale picture of groundwater supplies, which complements local well measurements.”. Hossain and his colleagues in the SASWE group take their education mission seriously. And the businessperson projecting future needs for harvest, delivery and storage of crops. Their plan is to take data from both satellites and use it in sophisticated computer models to help these countries improve hydrological forecasts and better manage their freshwater supply. River Valley’s prosperity trickles away.” If the Earth were a perfectly round sphere, any point on the planet’s surface would have the same average gravity field. The Middle East appears in the Atlas as a quilt of dark red and grey, indicating arid and extremely high water stressed areas where users withdraw 80 percent or more of the available, annually renewable surface water every year. Farmers moved in, drilled wells, and planted new cornfields. Managed sustainably, it can support food production and growing cities and businesses. “We need to understand the impact we’re having on groundwater from pumping and land-use activities and how that is playing out over time,” Alley said. Thirty years later, towns shrivel as farms decline and families leave for greener pastures. As part of their education mission, the group plans to host and train staff members from the Institute of Water Modeling in Bangladesh. Summer 2006: 4–10. Scientists use a pair of new satellites to keep up with groundwater resources. Science 305, doi: 10.1126/science.1099192. Society depends on the balance in distribution of Earth's water. It will be gone.”, Despite the estimated 16 million cubic kilometers (3.8 million cubic miles) of groundwater flowing under the Earth’s surface, wells and springs often fail to provide enough water when and where it is needed. But how do gravitational differences tell scientists about the presence of groundwater? NASA and JAXA are now planning a new satellite mission for 2013 called the Global Precipitation Measurement mission. Scientists can then track differences in the Earth’s gravity field from data retrieved from the GRACE satellites, improving their understanding of how water is moving and cycling around the planet. doi: 10.1029/2006GL026962. This monthly series will introduce you to NASA Earth Explorers, young and old, with a variety of backgrounds and interests. (Courtesy Sean Swenson). orbit. When groundwater dries up, so can the communities In collaboration with Utrecht University in the Netherlands and Deltares, a Dutch water research organization, we are preparing more detailed models of groundwater. "This is where GPM could really make an impact," Hossain said. "If you could know the rainfall in upstream countries ... you could put the data in a (computer) hydrologic model that could predict for the next couple of days what the river level might look like.". At WRI, we are planning a new global groundwater data layer for the Aqueduct Water Risk Atlas as a first step. In 2016, NASA plans to launch another hydrology satellite mission, called Surface Water and Ocean Topography, in partnership with the French space agency. land, computed from four years of GRACE gravity data. A satellite’s orbit above Earth is partly determined by gravity. While you know the water comes from an aquifer somewhere beneath your feet, it's invisible, diffused throughout layers of soil and rock. You don’t have to pay for the water you use or the electricity that powers your pump, so you let the pump run. Irrigation allows farmers to grow water-thirsty corn on the NASA and the German Research Institute for Aviation and Space Flight (Deutsche Forschungsanstalt für Luft und Raumfahrt) launched two new satellites, flying on the same track about 220 kilometers (137 miles) apart and 500 kilometers (310 miles) above the Earth. Draining an aquifer is therefore very different from draining a reservoir, where you can see the water level drop. The country is prone to flooding because it sits on the Ganges delta. groundwater comes and goes, each year, in various regions; red indicates high Swenson said, “The traditional way to measure groundwater is to dig a well and monitor the water-table level in the well, but a well’s water level doesn’t translate exactly to groundwater storage. And they regularly visit middle schools and high schools in rural Tennessee to share their enthusiasm with students about hydrology and management of water resources. It gave rainfall maps of the tropical regions near the equator, which get two-thirds of the world's total rain. In the 1970s, new irrigation technology made it possible to grow corn, which is much more lucrative than dryland wheat, in this sandy region. The Gravity Recovery and Climate Experiment (GRACE) satellites showed that many of the world’s biggest aquifers are being depleted at a much faster rate than they can be replenished, from the Middle East, India, North Africa and Central Asia to California’s Central Valley. In rural areas, that rises to 90 percent.” Whether for personal or commercial use, humans heavily depend upon the availability of groundwater. You and your neighbors, and other farms, companies and cities around the world, keep withdrawing water from these underground sources with little regard for how much water they use and how much is left. Despite the challenges, Alley believes that regional officials and scientific researchers remain tuned in to the need to measure the essential resource that groundwater provides. relatively arid plains of the western and midwestern United States. However, mountains, deep oceanic trenches, and other features cause minute changes in Earth’s gravity. By combining ground and space observations, the USGS and other national agencies can obtain a more comprehensive picture of groundwater availability across the United States. Right now, an IWM staff member is pursuing a master's degree focusing on understanding how to use satellites for real-time flood forecasting. “Basically, different aquifers store different amounts of water,” he said. Wheat needs more water than rains provide, especially during the dry season. A "We want to inspire the future generation of Earth scientists to pursue a career in one of the science, technology, engineering and math fields," Hossain said. Still another challenge for Alley exists in the very nature of groundwater. Rivers such as the Ganges and the Mekong originate in one country but cross several boundaries. People have an incentive – and no disincentive – to tap as much groundwater as they can. In southwestern Nebraska, a boom fueled by groundwater is going bust. That motivates WRI’s Water Team to focus on other key contextual elements: the combined effect of competition for surface water, groundwater depletion, and sharpening our comprehensive understanding of groundwater resources themselves, from current water table levels to sustainable withdrawal rates and more. For instance, five different countries share the Niger River basin in Africa. “Around the world, the availability of groundwater has actually affected the economic success or failure of a region,” said Sean Swenson, a researcher in the Advanced Study Program at the National Center for Atmospheric Research (NCAR). We're looking for students, teachers, scientists and others who are working with NASA Earth science data and imagery to better understand our home planet. mass variability in the Earth system. In the midst of California’s current epic drought, with no natural replenishment of aquifers and over-pumping, groundwater tables are declining alarmingly. Without knowing when the aquifers will go dry, or when water tables will sink so low that they are effectively inaccessible, users and water managers are blind to the scope and severity of their problems. On a national level, the USGS assesses the nation’s water supply, but determining if the regional water supply matches the regional need challenges local, state, and national agencies. Send your nominations to Dan Stillman: dan_stillman@strategies.org. So you drill a well. But truly understanding the nature of this critical resource, how much groundwater there is, how long it may last in different places at current rates of extraction, and what sustainable recharge rates are, is essential for many countries’ future economic development. Swenson S., P. J.-F. Yeh, J. Wahr, J. Famiglietti. Tapley, Byron D., et al. The Tropical Rainfall Measurement Mission run by NASA and the Japanese Aerospace Exploration Agency was the first satellite dedicated to rainfall measurement. People have long depended on groundwater for drinking water, Too little, and life can come to a halt. Hossain uses NASA satellite data to help Bangladeshi authorities monitor their water resources and prepare for water-related disasters. Many developing nations in Asia, Africa and South America have strong wet and dry seasons. But overuse California’s Central Valley is another exceptionally productive agricultural region that raised red flags for groundwater depletion in the GRACE analysis. Faisal Hossain, a civil and environmental engineering professor at Tennessee Technological University, understands this all too well. Bangladeshi authorities today can predict flooding only up to three days ahead of time, and often with low accuracy. However, he has found a number of obstacles in the way of a national program. Melting glaciers due to changing climate are also a threat -- half the country would be submerged if sea levels rose by one meter. During the last two years, Swenson has repeatedly confirmed that satellites can provide a method to measure groundwater over entire regions. You need to know the properties of the soil subsurface and the aquifer composition to actually determine that.” These aspects of the groundwater system help determine the amount of groundwater that an area will typically store. trailing satellite, scientists can determine changes in the Earth’s gravity. 2004. In December 2009, Hossain used satellite data to show that dams in arid and semi-arid regions of the world have created heavier storms with more rainfall, which have increased the possibility of flooding. ", http://www.nasa.gov/audience/foreducators/using-satellites-track-water.html. NASA’s twin Gravity Recovery and Climate Experiment (GRACE) satellites can detect groundwater by measuring subtle variations in Earth’s gravity. With this larger picture, the USGS, state, and local decision makers could work together to conserve shrinking groundwater. Yet groundwater resources sprawl across huge sections of land, crossing community and political boundaries and making it hard to understand how much water actually flows under any given tract of land.

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