Cities change storms, but the impacts depend on the storm itself
New findings could help reduce urban flood risks and improve planning for extreme weather
Texas A&M University
Cities don’t just change the landscape, they change the weather. According to a new study analyzing tens of thousands of rain events in Texas, whether urban areas make rain worse, lighter or simply different depends strongly on the type of storm.
The research, published in Nature, examines more than 40,000 warm‑season storms that passed over or near Dallas–Fort Worth, Austin, San Antonio and Houston between 1995 and 2017. By sorting storms into distinct categories and tracking their three‑dimensional structure using weather radar, scientists found that the four urban areas strengthen some storms while weakening others.
The findings help explain why previous research on urban rainfall has often produced conflicting results — and why blanket statements about cities being “wetter” or “drier” miss the nuance of how storms actually work.
“Different storms are driven by different physical processes,” said Dr. John Nielsen‑Gammon, a Texas A&M University atmospheric scientist and a co-author of the study. “Once you separate storms by type, the patterns became much clearer.”
Looking at storms one by one
Rather than focusing on long‑term rainfall averages, the researchers took an event‑by‑event approach, tracking individual storms as they formed, moved and dissipated. Using detailed radar data, they grouped storms into five common types:
- single‑cell thunderstorms
- larger isolated storms
- cold frontal storms
- warm frontal storms
- tropical systems, including hurricanes
Cities boost pop‑up storms
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.
The effect was especially noticeable at night, when cities remain warmer than their surroundings.
“Urban areas hold heat after sunset,” said Nielsen‑Gammon, who is also the Texas State Climatologist. “That retained warmth can continue to fuel storms overnight, when similar storms over rural areas are more likely to weaken.”
The researchers found similar urban effects for larger isolated storms, which last longer and cover more area than single‑cell thunderstorms. These storms were also more frequent over cities and showed stronger rainfall signatures, making them a significant contributor to urban flooding risk.
While these storms are usually short‑lived, they can produce intense rainfall over small areas, increasing the risk of flash flooding in cities, where a lot of the rain can't just soak into the ground.
Cold fronts weaken as they cross cities
The study found a different response for cold frontal storms, which are large, organized rain systems 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 roughly 16% to 28% compared with rural surroundings.
The researchers suggest that urban heat and roughness (the disruption buildings and other structures create in wind flow) disrupt the lower part of the storm system as it moves across the city.
“Cold front rainfall is driven by sharp temperature and wind differences,” Nielsen‑Gammon said. “As they move into the warmer and more turbulent urban environment, those contrasts can weaken, reducing rainfall intensity.”
Interestingly, the study found hints that cold fronts sometimes intensify slightly just before reaching a city, likely because the warmer urban air can sharpen the temperature contrast ahead of the front.
Warm fronts and tropical storms respond differently
Warm frontal storms showed modest signs of intensification over cities, though the changes were smaller and less certain than for other storm types.
Tropical systems, including hurricanes, did not show consistent changes in how often they occurred or how intense they were over cities. However, the structure of rainfall shifted slightly, with heavy rain forming lower in the atmosphere over urban areas — a detail that could influence flooding behavior on the ground.
“These larger systems are driven mainly by ocean heat and larger-scale wind patterns,” Nielsen‑Gammon said. “Urban effects don’t disappear, but they’re secondary compared to those factors.”
Why this matters for growing cities
The study’s results suggest that storm type matters for how cities experience extreme weather and for how they should prepare.
Urban planners often rely on averaged rainfall statistics to design drainage systems and flood controls. That approach may miss the fact that the storms most enhanced by cities are short‑duration, high‑intensity events, which are particularly dangerous in urban landscapes.
“If you design only for region-wide averages, you can underestimate the kinds of rainfall that actually cause the most damage,” Nielsen‑Gammon said. “Understanding which storms cities amplify helps planners target the real risks.”
The researchers say storm‑specific insights could improve flood resilience, emergency planning and weather forecasting in urban areas.
“Asking whether cities get more or less rain is the wrong question,” Nielsen‑Gammon said. “The right question is which storms are affected, because that’s what determines the risk people actually face on the ground.”
This research was funded by NASA and the U.S. Department of Energy.
By Lesley Henton, Texas A&M University Division of Marketing and Communications
###
Journal
Nature
Article Title
Divergent Urban Storm Response to Convective, Frontal, and Tropical Systems
Article Publication Date
20-May-2026
