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http://www.nasa.gov/topics/earth/features/tx-drought.htmlTexas Drought Visible in New National Groundwater Maps
11.30.11
The record-breaking drought in Texas that has fueled wildfires, decimated crops and forced cattle sales has also reduced levels of groundwater in much of the state to the lowest levels seen in more than 60 years, according to new national maps produced by NASA and distributed by the National Drought Mitigation Center at the University of Nebraska-Lincoln.
The latest groundwater map, released on Nov. 29, shows large patches of maroon over eastern Texas, indicating severely depressed groundwater levels. The maps, generated weekly by NASA's Goddard Space Flight Center in Greenbelt, Md., are publicly available on the Drought Center's website.
New groundwater and soil moisture drought indicator maps produced by NASA are available on the National Drought Mitigation Center's website. They currently show unusually low groundwater storage levels in Texas. The maps use an 11-division scale, with blues showing wetter-than-normal conditions and a yellow-to-red spectrum showing drier-than-normal conditions. (Credit: NASA/National Drought Mitigation Center)
"Texas groundwater will take months or longer to recharge," said Matt Rodell, a hydrologist based at Goddard. "Even if we have a major rainfall event, most of the water runs off. It takes a longer period of sustained greater-than-average precipitation to recharge aquifers significantly."
The maps are based on data from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites, which detect small changes in Earth's gravity field caused primarily by the redistribution of water on and beneath the land surface. The paired satellites travel about 137 miles (220 km) apart and record small changes in the distance separating them as they encounter variations in Earth's gravitational field.
To make the maps, scientists used a sophisticated computer model that combines measurements of water storage from GRACE with a long-term meteorological dataset to generate a continuous record of soil moisture and groundwater that stretches back to 1948. GRACE data goes back to 2002. The meteorological data include precipitation, temperature, solar radiation and other ground- and space-based measurements.
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