Trees Modify the Urban Microclimate

Abstract

A person's feeling of thermal comfort is affected by environmental conditions, including solar radiation, air temperature, wind, humidity, longwave radiation, and precipitation. Trees modify all of these variables and therefore affect individual thermal comfort. Shade and wind protection are wellrecognized efforts. But trees and other vegetation also contribute to cooling the air by the evaporative process of transpiration. An urban shade tree can produce as much cooling as five room air conditioners running 20 hours a day. The lack of transpiring vegetation in cities is one reason why cities are often several degrees hotter than the surrounding countryside.