Austin is repelling rain; other cities attracting it — UT study discovers

AUSTIN (KXAN) — If you've ever seen rain on radar moving toward a city suddenly split in two, as if something was blocking it from reaching the city, you may have joked about a forcefield being responsible. That joke may actually be the truth. A recent study done by researchers with the University of Texas found cities are capable of repelling rain.

"We have known that cities can change temperatures," said Dev Niyogi, a professor of geological sciences and environmental engineering at the University of Texas. "We have also started to know that cities can change rainfall."

Niyogi and a team of researchers from around the world wanted to know more about how cities are influencing rain.

They found different factors play a roll:

• Tall buildings, which can deflect wind.
• Roads, parking lots and concrete which make the city warmer.
• Green spaces, which cool parts of the city.
• Pollution, which influences heat and ozone levels.

For a city to influence the weather, it must have a diameter of 25-kilometers, about 15 miles across. Niyogi and his team found another factor that impacts the weather: its shape.

How a city's shape influences the rain

"Whether they are square, whether they are round, whether they elongate it does have an impact in the manner in which thunderstorms get formed, where they form, whether they come over the city," Niyogi said.

According to the team, there are four types of city shape:

• Starship/circular shape with a center spoke that stretches out in a circle: Think Paris or Indianapolis.
• Square shaped, with blocks of buildings spreading out by roads: Niyogi used Beijing and Houston as examples.
• Triangle shaped: Niyogi referenced coastal cities where most people live along the coast and then the cities tapers off behind it.
• Rectangular cites that follow a road or river: Austin is this shape, both following the local water features but stretching north along I-35.

Niyogi's team found circular cities actually attract rain. "The circular one clearly has the largest impact, because that's where the storms can come in, they can have an interaction."

Rectangular cities, like Austin, actually repel rain.

Designing a city to effect the weather

Niyogi said understanding the impact cities have on weather can help us direct the weather where we want it.

"Maybe there is a way that we can design Austin or any city we live in in a way that it can make it possible that there is a slightly more chance that it rains where we want it to rain."

This could be an aquifer or lake. Niyogi said in areas like the southwest, where water is becoming more scarce, this method could be essential.

Niyogi pointed out we now have enough knowledge to do this. His team works with city planners to do this around the world.