Environment / Earth Science News

The Unique Climatic Zone Known as Cities

Recent research shows how spaces like urban canyons create distinctive weather patterns—and how to prevent them from causing weather disasters.

by Joseph Calamia

From the November 2010 issue; published online January 30, 2011  (

http://discovermagazine.com/2010/nov/30-unique-climatic-zone-known-as-cities)

Cities may feel like the antithesis of the natural world, but they obey the same rules as do the most pristine patches of wilderness. Just like mountains and valleys, buildings and pavement create their own distinctive environments—and none so distinctive as urban street canyons, the spaces between high-rises and above the streets that run between them. Studies show that the shape of street canyons (the length of blocks and the height of buildings relative to street width) strongly influence the local climate. Urban climatologists are working to predict how canyon design can affect temperatures, winds, and the concentration of pollutants. Learning how to optimize these spaces is an increasingly urgent problem: As of 2008, the urban environment has become simply “the environment” for the majority of the world’s population.

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A Tree Grows in Manhattan  Although large areas of vegetation such as parks reduce urban heat and pollution, a2008 wind tunnel test (pdf) found that a single line of “avenue” tree plantings can actually make conditions worse by hindering winds that would otherwise bring in fresh air.

Taking it to the Streets  Many air quality studies rely on data from monitoring stations and Earth-observing satellites, but smaller sensors allow individuals to collect samples on their own. Researchers at MIT have developed a bicycle that can record pollution levels and upload the data via smartphone to create an online map for city planners.