The Urban Microclimate and Environmental Issues

Cities do not merely occupy the landscape; they create their own distinctive local climate, or urban microclimate, that differs measurably from the surrounding countryside. The most important feature of this microclimate is the urban heat island (UHI), the tendency for urban areas to be warmer than nearby rural areas, particularly at night. The temperature difference is typically a few degrees Celsius, though under calm, clear conditions it can reach five to ten degrees, and occasionally more in very large cities.

Several factors combine to produce the urban heat island. First, the materials of the city—concrete, brick, asphalt, and stone—have a high thermal capacity, absorbing solar energy during the day and releasing it slowly through the night, so cities cool down far less than fields d