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Evidence

How The Shape Of Your City Determines The Weather

New research shows how our streets and buildings influence storms, wind, and temperature. So could we "design" the weather?

Photo: jakubtravelphoto via Shutterstock

Humans have changed the planet so permanently and dramatically, scientists had to coin a special geological name—the anthropocene—just to describe it. And you might not realize it, but the weather patterns you live with everyday are a direct product of our busy urban cores. Yes, we’ve even altered the way weather moves around the atmosphere.

The shape of our buildings and streets dramatically change the weather in cities, say the authors of a study in the journal Boundary Layer Meteorology from École Polytechnique Fédérale de Lausanne. In their study, environmental scientists Marco Giometto and Andreas Christen ran simulations on a 3-D model of Basel, Switzerland, to show how the shape of buildings create atmospheric turbulence and suck up heat and pollution into the air. Using "large-eddy simulations," which model how wind moves around buildings, they were able to develop a more nuanced picture of what really happens to storms and wind when it blows over the urban fabric. Our current weather models are incredibly crude in comparison, and often deeply wrong.

To understand storms, heat, and wind, you have to look at cities—and as it turns out, there are plenty of existing examples of cities that shape the weather, either intentionally or by accident.

Atlanta’s Thunderstorms

One classic example of this effect comes from Atlanta, which experiences an unusual number of storms compared to nearby areas. A study in the Quarterly Journal of the Royal Meteorological Society this spring explained why, showing how Atlanta's unique urban geography plays a role.

First, there's the fact that the city is warmer than nearby areas due to its dense building grid and pavement (you've probably heard this described as the "urban heat island" effect), which creates a difference in pressure to increase storms. Second, its tall buildings create turbulence that kicks up the heat at street level and creates choppy air patterns. Third, increased levels of aerosol in the atmosphere during the workday may also play a role as Atlanta magazine explains, with pollution making storms even worse. "Storms are more likely on weekdays, when pollution is higher, than weekends," writes Rebecca Burns.

A similar phenomenon has been observed in other cities. In New York, storms tend to get split in half because of something called the "building barrier effect," and tends to see more storms than the surrounding area because of its heat island. In Indianapolis, scientists observed that storms tend to break up into choppy pieces over the city. "While we cannot control a large thunderstorm, our research does bring up the possibility that the impact of these thunderstorms can be affected by land-use planning," said atmospheric scientist Dev Niyogi at the time—suggesting that urban planners could even help mitigate storms with design.

See the full video herevia Edge-cdn

Stuttgart’s Air Channels

So, by the same logic, could architects design buildings and cities that purposefully shape the weather for our benefit? Could we "design" the weather? Giometto and Christen say that cities have been shaping their topography to change the climate—today known as urban climatology—for a long time.

Take Stuttgart, Germany. In the 1930s, meteorologists ran experiments on how to disguise the city with faux-fog during wartime. They discovered the haze moved more quickly in certain areas of the city, the Office of Environmental Protection explains. Eventually, this led urban planners to preserve "ventilation channels" or "lanes" as the city developed, codifying them as part of its master plan—today, these lanes help move cool, clean air down from the surrounding mountains through the city at night, pushing out pollution and hot air.

But outside of Stuttgart, there aren't many cities that are thinking about how their master plans could make their climates healthier, cleaner, or less stormy. "The reality though is, with few exceptions, the knowledge is usually only translated at the level of individual buildings or maybe blocks," Giometto and Christen say. An architect might care how wind reacts to his or her facade design, but cities aren't thinking holistically about how whole neighborhoods could be designed to be naturally cooler and cleaner.

In theory, designers could "select options that prevent unnecessary gusts at street level (affecting pedestrians and traffic)," the duo writes, or even "find ways so urban form enhances the dispersion of unhealthy pollutants, and be used to assess where wind can help to save or even generate energy."

Their published models of how weather interacts with buildings are meant to show how meteorologists could predict urban weather more accurately, and they could easily "guide intelligent design," too. It's easy to imagine a designer, or an entire city council, reverse-engineering the shape and layout of development based on the best weather pattern. It's not terraforming, it's aeroforming.

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