Austin rain dome: Do cities really deflect rain?

AUSTIN (KXAN) – Research conducted by several Jackson School of Geosciences members provides global evidence of noticeable urban precipitation anomalies, especially in hot and humid climates.

Professor Dev Niyogi and his colleagues including Ph.D. candidate Xinxin Sui examined over one thousands cities worldwide. They found that more than 60% of cities across the globe and their downward regions are receiving a surplus in precipitation than the surrounding rural areas.

They found that urbanization is evidenced to affect the formation, movement, and enhancement of precipitation by modifying the regional atmospheric boundary layer.

Niyogi and Sui are optimistic that their findings will continue to foster the development of more resilient cities in the future.

Meteorologist Tommy House spoke with the scientists about their research.

Meteorologist Tommy House: Walk me through what your objectives were in conducting this research.

Professor Dev Niyogi: So when we think about urban areas, we know that we already have this phenomenon called ‘Urban Heat Island,’ meaning cities are generally warmer than the surrounding area, but we don’t necessarily think of cities changing rainfall. And we had done some work before in Austin, where we had shown that cities can actually repel rainfall, that instead of coming, they were going away from it. And so the question was, was this something which was when it’s Austin-centric? Was it something only a few cities have, or is this something you can see as a global signature? And so that was the motivation in trying to understand that is the effect of the city on rainfall, a local thing or a global thing?

House: What are some ways urbanization influences the climate?

Niyogi: So the way cities affect our temperature is well known. You have infrastructure. You also have all the human metabolism, so to say, people living here and we emit energy, and so cities are warmer than the surrounding area, so that’s the first aspect. But what happens in the state city doesn’t just stay in the city, Vegas or otherwise, and it also has something an impact in the atmosphere above it. And so you have the region over the city, and much larger area over the city, where the atmosphere is very different as compared to a rural or a Peri urban region. And so when you have a storm coming in, it encounters this new atmosphere. And by virtue of that, it can either get more intensified, and then you can create more storms over the city, or it can get deflected and move away from the city. And so it is issues like, what is the height of the buildings? How much green infrastructure do you have? What kind of shape you have in the city. Do you have cities in topography like in Austin, or do you have it in a relatively flat regions, like in Houston? Other places, all of those things and the general climate, whether it’s a monsoon system or a typical mid latitude system, all of those things would matter.

Xinxin Sui: Yes, as Professor Niyogi mentioned, the urban heat Island is one of the most important factors that can influence the regional rainfall change, and another factors, like the tall buildings in the cities, is also increased the roughness. So some people find when there’s a storms is approaching the cities. They may change their structures and other factors, like aerosols, especially in cities, the anthropogenic aerosols coming from our cars and also industries. So this aerosols can be important cloud condensation nuclei. It helps to initiate a storm event.

Niyogi: So the particles, or the aerosols, if you have seen your salt, sometimes might have moisture in it, and when you’re trying to shake that salt, it that salt shaker, the salt doesn’t fall through. So it is the same way, when you have these particles in the atmosphere, they can attract the moisture, and when you have millions of such particles or aerosols, they can have lot of moisture available. And so when the conditions are right in terms of the temperature or the instability, all that moisture can get concentrated and get into your rain. That’s one of the mechanism by which the city, the pollution, the rains, all can be linked.

House: In your research findings, you wrote, this advancement holds promise for projecting extreme precipitation and fostering the development of more resilient cities in the future. You mentioned the Austin city council recently formalized the UT City-Climate CoLab, which is the framework for taking advantage to help build cities. Can you elaborate on that?

Niyogi: There’s one thing when we are doing research and you write a paper about it, and there’s another thing that you take that research and actually apply it where, in a way, it can help improve communities, the living experience we have in the city. This is not a simple process. It is sort of like you could have a drug discovery, but the actual medicine requires a pharma industry to work with you in the same way you have the setup required that when you want to improve cities, you need to partner with the city. And Austin recognizes that. So this is the first place where. Where Austin as a city, and the academia and the community has come together and created the UT-City Climate CoLab. This was recently passed as infrastructure for the city, and we are working together to take exactly this kind of research where we understand something from a world class study, and then say this is how it can be used in terms of translating how Austin develops. Should we have more taller buildings? Should we have more wider footprint? Should we have more trees? Should we have more grassland? And if so, where should we buy this area? And where should we restrain and refrain from growth, or where should we encourage growth? All those kinds of things in terms of helping city becomes livable in terms of cooler temperatures, but also access to water in the longer run, those would be the kind of things that we can do through the CoLab. And we are very excited about this.

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