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Texas weather has once again shifted between extremes, with the state swinging from a fairly wet spring into conditions that some are calling a flash drought.
After a relatively cool, wet spring, hot and dry temperatures throughout July and August have led much of the state to shift into drought conditions, according to the latest U.S. Drought Monitor. Bexar County is now considered “abnormally dry.”
“Texas has a lot of variability in its weather and the extremes are fairly large,” said John Nielsen-Gammon, Texas State Climatologist and a professor at Texas A&M University.
San Antonio also sweated through 12 consecutive days of triple-digit heat, from Aug. 8 through Aug. 19, according to National Weather Service data. That’s the third-longest streak of 100-degree-plus days on record for San Antonio, said Nick Hampshire, NWS meteorologist.
“We’ve had a persistent high-pressure system that’s kind of stayed over the southern plains,” Hampshire said. “Everything’s been dry and hot.”
One important regional measuring stick of drought conditions is the level of the Edwards Aquifer, the vast underground rock layer that holds the San Antonio area’s largest supply of drinking water.
Since May, the aquifer’s level has dropped from a high of 685 feet to just above 666 feet above mean sea level as of Wednesday. That’s according to data from the J-17 well located at Fort Sam Houston that measures the aquifer’s level below San Antonio.
The drop in the aquifer level has caused the Blue Hole spring at the headwaters of the San Antonio River to run dry, with nearby San Pedro Springs flowing less vigorously than it did earlier this year.
Statewide, Texas only has experienced two years in which July and August have been drier than in 2019, Nielsen-Gammon said. Those ultra-dry years were 2000 and 2011, he said. In 2011, the state’s water supplies began to suffer as Texas slipped deeper into its most severe recent drought; 2000 was a comparably parched year, though the dry spell didn’t last as long as the roughly 2010 to 2015 drought.
“There are still 10 days left in the month, so we could even still see rain,” Nielsen-Gammon said, but “that might still leave us in top 10.”
It takes more than heat and lack of rainfall to make a flash drought, Nielsen-Gammon explained. The warm season needs to have been rainy enough for plants to grow rapidly before moisture stops dropping from above.
“The plants start rapidly depleting the moisture in the soil, so things dry out really rapidly, not just because the air is dry but because the plants are sucking up all the moisture,” he said. “That’s the sort of thing we’re seeing in much of the state.”
Dry grasses and brush are fueling wildfires in drier parts of the state. The Texas A&M Forest Service, the state’s leading wildfire response agency, logged 54 fires that consumed more than 28,000 acres between Aug. 12 and Aug. 19. The largest of these fires have been in North Texas, Central Texas, and West Texas.
The risk of tree canopy fire in juniper and live oak forests, the type of vegetation that blankets the Hill Country surrounding San Antonio, is increasing as moisture levels drop, according to the Forest Service’s latest fire potential update. San Antonio is among the large urban areas in the U.S. most at risk for wildfire, even though the city has not yet seen a California-level blaze.
Some relief soon could be in sight with forecasters predicting isolated thunderstorms and temperatures in the low 90s in the coming days. That’s because of low-pressure systems moving into the area and a weakening of the strong high-pressure ridge that’s been sitting over Texas, Hampshire said. Still, that’s probably not enough to bring sustained, days-long rainfall.
For that, he said, it would probably take a tropical storm.