Historic drought of unprecedented proportions has fueled wildfires, decimated crops, and forced ranchers to sell their cattle in Texas. It also has reduced levels of groundwater in much of the state to the lowest levels seen in more than 60 years. That's made quite evident by new national maps produced weekly by NASA and distributed by the National Drought Mitigation Center at the University of Nebraska-Lincoln.
A NASA groundwater map made Nov. 28 shows intense maroon over East Texas, indicating severely depressed groundwater levels. Produced weekly by NASA's Goddard Space Flight Center in Greenbelt, Maryland, maps are available on the Drought Center website, at the University of Nebraska-Lincoln.
"Texas groundwater will take months or longer to recharge," says NASA hydrologist Matt Rodell, 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 the Earth's gravity field caused 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 use a computer model that combines measurements of water storage from GRACE with a long-term meteorological dataset, for continuous record of soil moisture and groundwater that stretches back to 1948. Meteorological data includes precipitation, temperature, solar radiation, and other ground- and space-based measurements.
The 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 recent dryness over the final week of November occurred less than 2% of the time between 1948 and present.
GRACE data also distributes soil moisture maps, updated each Tuesday as well.