Several natural factors make our region especially prone to sudden flooding.
TEXAS, USA — South Central Texas is considered the most flash flood-prone region in the country. This is why our region is also known as Flash flood alley. Jason Runyen, the warning coordination meteorologist from the National Weather Service, says the reason comes down to a combination of geography and weather.
“This region of the country is prone to flash flooding because there’s a number of different ingredients that we have that are unique to this region,” said Runyen. “The first is our proximity to moisture with our proximity to the Gulf.”
When heavy rain, fueled by moisture from the Gulf, hits the shallow soil and limestone bedrock of the Hill Country, it cannot soak in and instead runs off into creeks and streams almost immediately.
“The water runs off quickly down into the creeks and streams,” Runyen said.
Rainfall rates are often the key driver in flash flooding. When storms produce several inches of rain per hour,, runoff can quickly exceed the capacity of streams and creeks.
“It only takes about two inches per hour to start causing issues with flooding,” said Runyen. “But you start getting three or four inches per hour, and you can quickly get into some Considerable to catastrophic type flash flooding in this region.
While we see the most activity in the spring and fall this is a year-round threat , as Flash floods can occur in any month.
“We’ve seen it in every month of the year, especially as we move into El Nino. We can get flash flooding in the middle of winter,” Runyen said.
Because these ingredients cause water to rise so rapidly, this area of Texas leads the nation in flash flood fatalities. A majority of those deaths are vehicle-related because many people underestimate the power of a relatively small amount of water.
“As little as a foot of water… can sweep a smaller car off the roadway. It’s less water than you think,” said Runyen.
To limit your risk, the National Weather Service recommends keeping your Wireless Emergency Alerts active on your phone and using a NOAA weather radio for accessible warnings. Above all, the advice for drivers remains the same.
“Turn around, don’t drown,” Runyen said. “Don’t attempt to cross that flooded roadway.”