What is the urban heat island?

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What is the urban heat island?

"Urban Heat Island" (UHI) refers to the tendency for a city to remain warmer than its surroundings. This effect is caused mostly by the lack of vegetation and soil moisture, which would normally use much of the absorbed sunlight to evaporate water as part of photosynthesis (a process called "evapotranspiration"). Instead, the sunlight is absorbed by manmade structures: roads, parking lots, and buildings. With little or no water to evaporate, the sunlight's energy goes into raising the temperature of those surfaces. After the sun sets, the city is so warm that it never cools down as much as the countryside around it, and so retains the heat island effect all night long. There is some evidence that the Urban Heat Island effect modifies the rainfall patterns around cities, at least in the summertime.

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