Cities appear to attract extra rainfall, a recent study from researchers at the University of Texas found. But Austin does not appear to be among them.
The study looked at rainfall data for 1,056 cities around the world and found that about 60% of urban areas tend to report more rainfall than their surrounding areas.
Study author Dev Niyogi, a professor at the Jackson School of Geosciences, says there are several reasons why.
For one, the built environment of cities warms the air. Warm air holds more moisture. Niyogi says it also drops the air pressure and can cause winds to converge toward a city, bringing more clouds.
Cities also have taller buildings. Those may slow or channel air flow in such a way that weather systems last longer. Finally, cities create more air pollution particles that act as little nuclei around which raindrops can form.
“Those pollutants can actually get into the clouds and do something like cloud seeding,” Niyogi said, referring to the practice of intentionally introducing fine particles into the air to encourage rainfall.
Houston topped the list among U.S. cities with the largest so-called “rainfall anomaly," reporting almost 5 inches more rain than surrounding areas on average.
“Houston is where we found one of those top cities where as the city grows, we are increasing the rains over the city,” Niyogi said.
The research might appear to debunk the much-debated idea that Austin gets less rain than surrounding areas. But, Niyogi said, there are still scientific arguments in support of the so-called “Austin rain dome.”
In fact, according to the study, 30% of cities get less rain than surrounding areas.
Niyogi said this can happen when nearby microclimates, regional topography or local development encourage clouds to “veer away” from urban centers.
In the case of Austin, the nearby Balcones Fault may play such a role.
“Austin is not unusual,” Niyogi said. "In the D.C. area, people have often referred to these storms as the 'beltway storms.' They seem to come toward the city, and then they seem to follow that beltway and go around the city.”
