A historic drought has depleted Texas aquifers to lows rarely seen since 1948, and it could take months — or even years — for the groundwater supplies to fully recharge, scientists who study NASA satellite data said Wednesday.
Climatologists, hydrologists and even local residents had suspected the drought that has parched Texas for 14 months was significantly hurting the precious aquifers that course beneath the Lone Star State. Data compiled by NASA satellites combined with information from the University of Nebraska's National Drought Mitigation Center confirm those fears.
"We can say with more confidence that yes, the groundwater storage is being reduced," said drought center climatologist Brian Fuchs.
Texas has received a little more than 12 inches of rain this year, which is 15.5 inches below normal, said Texas State Climatologist John Nielsen-Gammon. He noted that despite some recent rain, the deficit has actually grown since last month by about an inch.
NASA's Gravity Recovery and Climate Experiment, or GRACE, satellites are unique because rather than measuring light on wavelengths, they measure gravity based on mass variations, making them sensitive to changes in water on or below the Earth's surface, no matter how deep, explained NASA hydrologist Matthew Rodell. Scientists took that data and combined it with other information to create a numerical model that simulates the water redistribution after it rains. They were then able to conclude that the aquifers are at lows seen only 2 percent of the time since 1948, when mapping began.
"People rely on groundwater, especially in times like this when it's dry, because groundwater provides a reserve of water when it doesn't rain," Rodell said. "But we're in a deficit now. We're drawing down our bank account."
It doesn't look like those supplies will be replenished by rain in the coming months, Fuchs said. The La Nina weather pattern currently cooling the Pacific Ocean typically causes warmer, drier weather in Texas and other parts of the South. The best hope for rain, he believes, will be in the spring.
"The likelihood of recovery or any substantial improvements is probably not going to be there," Fuchs said.
The longer the drought persists, the more the groundwater is depleted — not only because rain is not recharging the aquifers, but also because more people are using that water. As the aquifers are depleted, some people may have to drill deeper wells, Rodell said. Others may not have that luxury; the wells may already be as deep as possible.
Some recent rains appear to have improved the soil quality in parts of Texas, Rodell said, but it will take much more to recharge the aquifers. A few days of constant rain could help, he added, but typically most of that rain runs off. Really, Texas needs a few rainy months — or a wet year — to replenish its groundwater supply.
"Typically, it's going to take months to years of above average rainfalls to bring aquifers back up," he said.
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