Texas Hill Country has a flooding trend, and climate change makes it more common.
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The floods overwhelmed the Guadalupe River in Texas, killing at least 24 people, and spurring desperate, continuing rescue efforts.
Texas Hill Country is no stranger to extreme floods. On the sturdy, gentle terrain that it is known will rapidly gather heavy rain on shallow streams and rivers that can explode into rapids like deadly flood waves swept along the Guadalupe River on July 4th.
According to the US Geological Survey, Guadalupe has been inundated more than 12 times since 1978, but the Independence Day flooding is the worst in history. The Raging River claimed at least 43 lives, officials said on July 5, with rescuers still searching for a missing child.
Alan Gerald, a recently retired storm expert in the National Marine and Atmospheric Administration, created a “terrifying” scenario that reduced rainfall by up to 16 inches on July 3rd and 5th in one of the places where several factors could be one of the worst.
Hill Country, a central and southern Texas region, is also colloquially known as the “Flash Flood Alley.” This is what Gerald, CEO of weather consulting firm Balance Weather, said because there is a trend towards fast and severe flooding when extreme rain falls. Rich, humid air from the Gulf of Mexico, renamed the Gulf of Mexico, moves over steep hills and allows heavy rain to be dumped.
On July 4, rain fell 3-4 inches per hour, with some locations recording up to 7 inches of rain flooding in just three hours, the National Weather Service said. The seven-inch rain is nearly 122 million gallons of water per square mile. More than 7 square miles, enough water to fill AT&T Stadium, home to the Dallas Cowboys.
The Guadalupe River responded quickly, rushing downstream towards Carville, a city of 24,000, and soared over 20 feet in several locations in a few hours.
What causes the heavy rainfall?
Gerald and Victor Murphy, a meteorologist with the National Weather Service, recently retired in Texas, said topography and timing were the biggest drivers of the storm.
The thunderstorm, which began on July 3rd and continued into the morning of July 4th, saw 10.33 inches of rain fall near Ingram, Texas, and spread in more than half a dozen counties in South Central, Texas, ranging from 3 to 7 inches.
Gerald said the area is close to the Gulf Coast, and it gets “very high rainfall rates” especially in the summer months.
“The bay is warmer than usual and the interference that travels through its currents can concentrate thunderstorm activity, especially in the area,” he said. On July 4th, it was all the cases focused on “the very wrong place.”
The top-level atmospheric interference was slammed by deep feathers of tropical moisture remaining from Barry, a tropical storm that landed in Mexico on June 29, Gerald said. It didn’t help that the storm, which formed on Independence Day, moved in the same direction as the Guadalupe River.
Hathim Sharif, a hydrologist and civil engineer at San Antonio, wrote a conversation article in the July 5th article.
The cliffs are lines of cliffs and steep hills created by geological negligence, Sharif said. “As warm air from the bay runs up the cliff, it can condense and throw away much of the moisture. That water quickly flows through the hills from many different directions, burying streams and rivers below.”
A weather balloon fired remotely by the weather service Del Rio in western Texas, Murphy said, exhibited near record moisture in the upper atmosphere. With that enormous amount of moisture serving as fuel, the winds hitting the cliffs in West Texas served as a kind of match that started the storm.
“When there’s a storm, they’re independent,” Murphy said. That’s also why the region continued rain and flooding on July 5th.
What role did climate change play in the floods in Texas?
Warming on the land, particularly on the Gulf Coast, has more frequently trapped extreme rainfall events in arcs across the United States, from Texas to the northeast. The area has always seen extreme rainfall occasionally, but today it is more frequent, according to weather services data.
Air increases by 7% with every 1.8 degrees increase in temperature. Gulf waters are often 3, 4, or 5 degrees warmer than usual. At one point this year, sea surface temperatures in the bays off the coast of Texas and Louisiana were above the usual 8 degrees.
“As shown again and again, post-event events, climate change, leads to wetier, more extreme precipitation events,” Kevin Reid, an associate degree in climate and sustainability programming at Stony Brook University, previously told USA Today.
Of the 140 years of the US weather record, more than half of 24 hours of rainfall has been set over the past 30 years.
Hill Country’s reputation for floods
A guide to Texas State Park reveals that flash floods are common and life-threatening.
“In hills, flash floods can attack little or no advance warning,” advises the guide. “Beware of changes in weather and seek early high altitudes.”
“Don’t camp on the low ground next to streams, canyons, or deep arroyos, because flash floods can catch you while they’re sleeping,” he says.
Overall, Texas is “and leading the nation in the deaths of the flood,” Sharif said. “Many of these flood deaths occur in the Hill Country.” Floods occurred in Hill Country on July 4-5, 2002. The area had been raining for 6 days of 40-45 inches. Guadalupe reached record heights at Canyon Dam. Seven people died in flash floods, with damage estimated at $250 million
USA Today’s national correspondent, Dinah Voyles Pulver, writes about climate change, violent weather and other news. Contact her at dpulver @usatoday.com or @dinahvp.
