On warm summer days with little or no wind, the air temperature in cities can be up to ten degrees higher than that of the surrounding countryside. This is a phenomenon commonly referred to as the "urban heat island" effect. This phenomenon happens when pavement, buildings, and other infrastructure   replace natural land cover. _ Unlike soil, paved areas contribute to runoff, which means that as paved areas increase, the amount of water available for evaporation   decreases. Moreover, urban areas have fewer trees and less natural vegetation which help to control the heat by providing shade and blocking solar radiation. The surfaces of leaves also provide water for evaporation which cools the air, further worsening the heat island effect. In particular, during summer, more energy is required to cool the insides of building and for refrigeration, thereby creating additional heat output. This in turn leads to higher ambient air temperatures, which can also significantly increase the formation of urban smog in an area, _ local air quality. Such a situation may directly affect public health with individuals more likely to suffer from heat exhaustion and the effects of asthma  . Which of the following is not a cause of the urban heat island effect?
The lack of trees The demand for refrigeration The blocking of solar radiation The construction of infrastructure.