The record-breaking drought in Texas that has fueled wildfires, decimated crops and forced cattle sales has also reduced levels of ground water 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.
ground water map, released on Nov. 29, shows large patches of maroon over
indicating severely depressed ground water levels. The maps, generated weekly
by NASA's Goddard Space Flight
Center in Greenbelt, Md.,
are publicly available on the drought center's website.
"Texas ground water will
take months or longer to recharge," says 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."
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 apart and record small changes in the
distance separating them as they encounter variations in Earth's gravitational
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 ground water 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.
color-coded maps show how much water is stored now as a probability of
occurrence in the 63-year record. The maroon shading over eastern Texas, for example,
shows that the level of dryness over the last week occurred less than two
percent of the time between 1948 and the present.
The ground water
maps are not the only maps based on GRACE data that the drought center publishes
each week. The drought center also distributes soil moisture maps that show
moisture changes in the root zone down to about 3 feet below the surface, as
well as surface soil moisture maps that show changes within the top inch of the
of these maps offer policymakers new information into subsurface water
fluctuations at regional to national scales that has not been available in the
past," says the drought center's Brian Wardlow. The maps provide finer
resolution or are more consistently available than other similar sources of
information, and having the maps for the three different levels should help
decision makers distinguish between short-term and long-term droughts.
maps would be impossible to generate using only ground-based
observations," said Rodell. "There are ground water wells all around
the United States and the U.S. Geological Survey does keep records from some of
those wells, but it's not spatially continuous and there are some big
also offer farmers, ranchers, water resource managers and even individual
homeowners a new tool to monitor the health of critical ground water resources.
"People rely on ground water for irrigation, for domestic water supply,
and for industrial uses, but there's little information available on regional
to national scales on ground water storage variability and how that has
responded to a drought," Rodell says. "Over a long-term dry period,
there will be an effect on ground water storage and ground water levels. It's
going to drop quite a bit, people's wells could dry out, and it takes time to
are the result of a NASA-funded project at the drought center and NASA Goddard
to make it easier for the weekly U.S. drought monitor to incorporate
data from the GRACE satellites. NASA's Jet Propulsion Laboratory, Pasadena, Calif.,
developed GRACE and manages the mission for NASA. The ground water and soil
moisture maps are updated each Tuesday.
Texas Drought Visible in New National Ground Water Maps
December 6, 2011