The structure of cities may affect the weather and the dispersal of air pollutants, a new study has found.

Aside from different activities in cities such as active transportation operations, industrial interventions and domestic events, which can contribute to heat and subsequent thunderstorms, the spaces between buildings also have a say.

The way winds are channeled and turbulence are generated may also influence the weather and air quality in a particular urban location.

Scientists from école Polytechnique Fédérale de Lausanne in Switzerland have discovered that air quality models and city representations do not represent significant characteristics such as energy and heat transfer in the lower atmosphere. Aside from that, the mechanisms that current sensors cannot detect are those that are highly valuable for more accurate weather models.

Simulating Wind Flow

Turbulence occurs when the wind blows over the city and buildings come in contact with the passing air mass. This turbulence goes up to the atmosphere and down onto the roads. The resulting effect is that more heat, pollutants and humidity are sent up from the ground. Meanwhile, more energy from the wind's turbulence depletes between open areas in the city.

Study first author Marco Giometto says that what they presented is about the importance of considering the space differences of cities — the distinct features that uniquely define each city.

Giometto adds that majority of city portrayals in weather models are derived from information collated from tower calculations made at a specific area in the city, which existing models estimate as an irregular piece of land. He further explains that heat, pollutants and humidity transport is calculated via mathematical interactions, which speculate that the city has a geometrically regular — a tough hypothesis.

To investigate, the team conducted detailed simulations of wind flow above and within the city of Basel, also in Switzerland. They compared their findings with that of wind tower measurements.

Findings show that for specific factors necessary in ascertaining local weather and pollutant dispersal, estimating the city as a regular patch of land may result in errors equivalent to up to 200 percent.

Out WIth The Old, In With The New

"Weather models obviously can't include detailed representations of all large cities," says Giometto. High-quality simulations need ample amount of time and resources, which forecasters are able to easily access. Therefore, effective weather models should go beyond approximating that cities are rigid patches of land. Instead, experts should develop new and more precise methods to represent urban locations as simple as possible so that it can be translated to computer models.

The study was published in the Journal of Boundary Layer Meteorology.

Photo: Lars Steffens | Flickr

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