After summer wildfires, why some areas are at high risk for flash floods
24 August 2022
Published by: https://www.kxan.com
USA – CENTRAL TEXAS (KXAN) — Amid an active summer wildfire season that led to several blazes in and around Central Texas, Monday’s forecasted rainstorm could spell flood risks for recently-burned areas.
Burn scars are areas where recent fires have stripped the vegetation from the region, leaving no buffer between the soil and the elements. That means there’s no trees, bushes or even leaves on the ground to soak up some of the rain, leading to supersaturation within the soil, said Karl Flocke, a woodland ecologist with the Texas A&M Forest Service.
When an area has been recently burned by a fire, that means the rain will hit the soil at a higher speed, washing off the ground into any surface water channels like canyons, creeks and rivers.
“Without that vegetation, a lot more water is going to run off the surface,” he said. “And in a large rain event like we’re potentially about to see, that can lead to increased risk of flash flooding over burned areas.”
For areas that saw wildfires during the spring, some grass has begun to grow in these areas, slowing down the soil’s absorption of the rain. But areas that saw fresher fires this summer — especially those on steep terrains — are particularly vulnerable to flooding.
At risk are areas where fires burned between hundreds and thousands of acres, such as the Big Sky Fire in Gillespie County.
“All of that is really up in the upper reaches of Crabapple Creek,” Flocke said. “So if a lot of water falls on that 1,000-plus acre fire, it’s all going to flow into Crabapple Creek.”
Ahead of Monday’s rainstorm, Flocke stressed the importance of residents following all local weather advisories, especially the National Weather Service’s flash flood watches and warnings. For people who live downstream from a recent fire, he added they need to pay close attention to rainfall and watch for low water crossings.
Along with flash flooding concerns, regions recently burned by wildfires are also at a higher risk for erosion. Flocke said that’s because a high volume of rainfall in a vegetation-less area will take the topsoil with it in a flood, making it more challenging for the landscape to recover in the future.
For any landowners impacted by recent fires — particularly those on higher elevations — Flocke recommended they reach out to the Texas A&M Forest Service and the Natural Resources Conservation Service for assistance with post-fire mitigation practices to prevent soil erosion.
