Tropical Storm Alberto didn't aid South Texas' drought as expected
AUSTIN (Nexstar) — South Texas has been experiencing a three-year drought, leaving the lower Rio Grande area in a critical state with two of the region's major water reservoirs at record-low levels.
In mid-June, the arrival of a Tropical Storm Alberto near the Texas Coast brought hope for relief, but it failed to deliver enough rainfall to help with drought conditions.
Dr. Mark Wentzel — a hydrologist in the surface water division at the Water Development Board — said there was an expectation for six or more inches of rain over a widespread part of South Texas.
"We saw an immediate impact in the drought monitor map, a 5% decrease in the area of the state impacted by drought in just that one week," Wentzel said. "So we saw a really good impact there that was mostly due to a one-category drought improvement and across the entire south -- the whole area impacted by Alberto."
This impact did not, however, appear in the region's water supply reservoirs.
"It's really because of the soil moisture in the area, that first rainfall that you get after you've been dry for so long," Wentzel said. "The soil just expands, soaks it in, and there's very little runoff that would go into your streams and make its way down to your reservoirs."
Wentzel explains this process as "priming the pump." He said that the initial rainfall after a long dry period will go straight into the ground, allowing the following rainfalls to produce runoff and enter the water supply.
"If they [South Texas] could get some additional moisture in coming weeks, they'd see some better runoff and some better water supply improvement," Wentzel said.
The good news is that the Weather Service has been tracking other storms that are queued up to possibly hit Texas in the coming weeks. The bad news is that storms of this caliber are known to be catastrophic to homes and infrastructure.
"It's tough. I mean, we'd like to have the extra rainfall," Wentzel said. "Particularly in areas where we need it, that we would get with a tropical storm or hurricane. But of course, along with that comes a storm surge on the coast, that comes flooding, and really in, in that aspect, Tropical Storm Alberto was almost ideal for us in that it didn't cause a lot of storm surge, it didn't cause a lot of flooding, although it did cause some."
The low water levels in South Texas' Amistad International and Falcon International reservoirs are partly due to reduced water deliveries from Mexico, which is also facing a drought. The 1944 treaty mandating water exchanges between the U.S. and Mexico is further complicated by these drought conditions.
Just because South Texas is experiencing severe drought does not mean the rest of Texas is. Wentzel said that people in the northeast and on the Brazos River are regularly dealing with flooding.
"Welcome to Texas," Wentzel said. "We're a big enough state that we can have flooding and droughts in the same week."
Wentzel said that it is typical for landscapes to recover more quickly than water supplies. Therefore, it is not unusual to experience storm activity that rapidly improves drought conditions on the landscape but takes longer to affect water reservoirs.