This week, San Antonio experienced one of the worst flooding events in nearly a decade, serving as a reminder of how quickly water can become dangerous.
Flash flooding is often underestimated, but it’s the second deadliest weather hazard in the United States, behind only heat.
Understanding the causes of flash flooding, its dangers — especially in urban areas — and how to stay safe when the skies open up is essential.
Regular vs. flash flooding
This week, storms “trained” over the same areas, pouring several inches of rain in a short period.
Creeks, rivers, and drainage systems couldn’t keep up, resulting in dangerous and devastating results.
It is important to remember how quickly water can move. It only takes 6 inches of water to move a human and less than 2 feet to move a vehicle.
Regular flooding occurs due to steady rainfall, snowmelt, or the release of water from upstream sources. This kind of flooding develops more gradually, often over hours or days, giving people more time to evacuate or protect property. While regular floods tend to be less sudden than flash floods, they can last much longer and cover wider areas.
A flash flood happens when heavy rainfall overwhelms the ability to absorb water in a very short amount of time. Unlike regular flooding, which develops gradually over hours or days, flash floods can occur within minutes.
Urban impacts of flooding
Cities are especially prone to flash flooding because they’re covered in concrete and asphalts that don’t absorb rain. When the water has nowhere to go, it rushes over land, gathering in areas such as underpasses, intersections, and drainage channels. When there is too much water, it can cause concrete to buckle, destroying roadways.
Even well-designed stormwater systems can become overwhelmed in extreme events like the one we just experienced. Urban areas also face high economic costs due to dense infrastructure and high population concentrations. Cleanup and repairs can take weeks or even months.
Rural impacts of flooding
Many areas across Bexar sit along normally quiet creeks and streams. When those waterways overflow, floodwaters can wash away soil, destroy fences and livestock, cut off roads and flood homes with little to no warning. In some cases, emergency response may be delayed simply because access is limited.
In some rural areas, flooding can also disrupt entire ecosystems and affect wildlife habitats.
Preparing for future floods
With climate change leading to more extreme weather events, both flash and regular flooding are becoming more frequent and intense.
If a flash flood warning is issued, move to higher ground immediately. Avoid low-lying roads, underpasses, and creeks, especially at night when it’s harder to see rising water. By understanding how different floods behave and where their impacts are most severe, communities can take steps to reduce the damage and keep people safe.
It is crucial to be prepared and know if you live in a flood-prone area. Monitor flood watches and warnings, listen to all emergency alerts and never walk or drive through floodwaters, even if they appear shallow. Turn around, don’t drown.
- Read more from the meteorologists on the Whatever the Weather page
- Download KSAT’s weather app for customized, accurate forecasts in San Antonio, South Texas or wherever you are
- Find the latest forecasts, radar and alerts on the KSAT Weather Authority page
