UTSA - The University of Texas at San Antonio
06/07/2022 | News release | Distributed by Public on 06/07/2022 03:49
UTSA researchers examine urban effects on thunderstorms in Southeastern cities
To accomplish this feat, the team developed a methodology to create an Urban Convection Ratio (UCR) for each city. The UCR compared the frequency of weakly-forced thunderstorms-which are storms driven largely by instability and moisture rather than the synoptic-scale lifting of air and wind shear-to the frequency of storms anticipated as a result of geophysical factors alone, allowing the researchers to isolate urban influences on thunderstorm activity.
Of the 32 cities in the study, these 10 had the largest UCRs:
- New Orleans, La.
- Memphis, Tenn.
- Tampa, Fla.
- Raleigh, N.C.
- Knoxville, Tenn.
- Atlanta, Ga.
- Sarasota, Fla.
- Miami, Fla.
- Norfolk, Va.
- Birmingham, Ala.
Although coastal metros such as New Orleans have historically made it more challenging to precisely identify urban effects on rainfall-due to their increased interaction with sea breezes and tropical disturbances-Debbage said the cities at the top of the list absolutely warrant additional investigation.
"I think this study sets the stage for future modeling work to more fully understand the specific physical mechanisms that explain the large UCRs in New Orleans, Memphis and Tampa," he explained.
While New Orleans, Memphis and Tampa could prove to be informative study sites for the urban rainfall effect, two other top 10 entrants offered even more striking insights.
"One of the more notable findings was that several relatively smaller cities like Knoxville and Norfolk exhibited significant thunderstorm enhancements," Debbage said. "This suggests that the urban rainfall effect is potentially widespread throughout the Southeast."
The researchers were also surprised to find that two urban areas they examined actually suppressed thunderstorm activity: Winston-Salem, N.C., and Hickory, N.C., which ranked third-to-last and last, respectively, in UCR size among the cities studied. In Hickory's case, the group surmises that the city's interactions with the mountainous topography of the Appalachians to the west could reduce thunderstorms. In addition to cities with large UCRs, these two areas certainly merit further analysis.
Moving forward, Debbage hopes to apply the UCR approach to additional urban environments beyond the Southeast. One of the driving forces behind his research is urban flood resiliency. A better understanding of the urban rainfall effect will inform city leaders and first responders on how to prepare for potentially hazardous weather events.
"To fully prepare for flooding, urban planners and emergency managers likely need to account for urban amplification of precipitation," Debbage explained. "It is, in many respects, a double whammy, where urban environments can increase the initial rainfall and increase runoff once the precipitation reaches the ground."