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A new study on rain events in Texas could help reduce urban flood risks and improve planning for extreme weather.
The Texas A&M Urban Flood Study found that cities can actually change the weather, depending on the type of weather event.
Researchers looked at over 40,000 warm‑season individual storm events in Dallas-Ft. Worth, Austin, Houston and San Antonio between 1995 and 2017.
The study looked at individual storms instead of long-term rainfall totals and sorted storms into distinct categories, tracking their three‑dimensional structure using weather radar.
Researchers found that cityscapes and urban areas strengthen some storms while weakening others.
Dr. John Nielsen‑Gammon is a Texas A&M University atmospheric scientist and a co-author of the study. Nielsen-Gammon is also the Texas State Climatologist.
He said the most dangerous types of urban storms are ones that are similar to the June 2025 San Antonio flood which killed 13 people.
"That sort of rainfall runs off quickly and can potentially overwhelm sewer systems and urban creeks and streams and culverts."
According to an overview of the study, the strongest and most consistent urban effect appeared in small‑scale thunderstorms, the kind that can pop up quickly on hot summer days.
Across all four cities, these local storms occurred 7% to 31% more often over urban areas than over nearby rural land. Radar data also showed that these storms tended to grow taller and more intense over cities, a sign of stronger upward motion in the atmosphere.
Cities can create what are referred to as “urban heat islands” which can cause storms to be more intense.
Nielsen-Gammon said many people incorrectly think that cities “repel” storms, or make storms go around them.
“People tend to perceive that cities inhibit rainfall, and actually that's true of people just about everywhere. They often ask me why do storms seem to go around them rather than hitting them,” he said.
“And of course that can't happen everywhere. So when we look at average rainfall totals, we don't see that sort of effect in cities or in the surrounding countryside," he said. "So that seems to be people's impression because they're expecting a storm that exists to hit them as it's moving toward them. But storm lifetimes, particularly thunderstorms, are often just a half hour to an hour long. So if you see it coming, it may actually be likely not to hit you.”
The study also found that urban areas can actually lessen the intensity of cold fronts as they pass through. Cold frontal storms are driven by temperature differences between air masses.
Cities did not change how often cold fronts occurred, but they did change their strength. When cold frontal storms passed directly over urban areas, their rainfall intensity declined by as much as 28% compared with rural surroundings.
The researchers said storm‑specific insights could improve flood resilience, emergency planning and weather forecasting in urban areas.
The Texas A&M study was funded by NASA and the U.S. Department of Energy and published in Nature
