Vegetation Helps to Lessen the Effects of Urban Heat Islands

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The urban heat island effect is a well-known side effect of living in a large metropolitan space. Large cities can be 2 to 5 °F hotter than rural areas because of the materials used in the construction of cities. Concrete, asphalt, stone, and metal all absorb and retain solar energy, but unlike more natural areas, they don’t release this heat back into the atmosphere.

Grasses, trees, and other vegetation have a natural heating and cooling cycle that is disrupted by urban structures. Vegetation cools the surrounding area as part of photosynthesis. Water that has been absorbed by the vegetation is released into the atmosphere, cooling the surface temperature of the surrounding area. The more surface area a plant has, the more it is able to take in and release water.


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What do plants have to do with the urban heat island effect? The abundance, or lack, of vegetation in a city can have an effect on how much heat the city retains. Basically, the more a city has invested in green spaces, trees, and other patches of vegetation, the more the heat island effect is regulated. However, if a city has been built up to the point where there isn’t a lot of greenery, the urban heat island effect can be very strong.

Map showing the urban heat island effect. Source: NASA
Map showing the urban heat island effect in the United States. Source: NASA

Understanding how vegetation influences a city’s unique urban heat island effect can help scientists and city planners learn how to meet their city’s needs. For instance, if a city experiences a change in temperature because of the urban heat island effect and a lack of vegetation, more residents may require water and cooling systems in their homes during the course of the year. This could influence energy usage, among other changes in a city.

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Mapping the urban heat island effect and how it interacts with varying levels of vegetation in urban areas is ongoing. These maps can be used for conservation efforts as well as providing a template for future city planning goals.

More: Vegetation Limits City Warming Effects – NASA, August 26, 2015

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