Normal temperatures of Tokyo go up higher than those of the surrounding area.Ī definition of urban heat island is: "The relative warmth of a city compared with surrounding rural areas." : 2926 This relative warmth is caused by "heat trapping due to land use, the configuration and design of the built environment, including street layout and building size, the heat-absorbing properties of urban building materials, reduced ventilation, reduced greenery and water features, and domestic and industrial heat emissions generated directly from human activities". Definition Tokyo, an example of an urban heat island. Description Mechanism of the urban heat island effect: the densely-built downtown areas tend to be warmer than suburban residential areas or rural areas. : 993 Compact, dense urban development may increase the urban heat island effect, leading to higher temperatures and increased exposure. Ĭlimate change is not the cause of urban heat islands but it is causing more frequent and more intense heat waves which in turn amplify the urban heat island effect in cities. Other options include green roofs, passive daytime radiative cooling applications, and the use of lighter-colored surfaces and less absorptive building materials in urban areas, to reflect more sunlight and absorb less heat. Heat can be reduced by tree cover and green space, which act as sources of shade and promote evaporative cooling. Effects within a city can vary significantly depending on local environmental conditions. Not all cities have a distinct urban heat island, and the heat island characteristics depend strongly on the background climate of the area in which the city is located. The UHI decreases air quality by increasing the production of pollutants such as ozone, and decreases water quality as warmer waters flow into area streams and put stress on their ecosystems. Increases in heat within urban centers increases the length of growing seasons and decreases the occurrence of weak tornadoes. Monthly rainfall is greater downwind of cities, partially due to the UHI. The term heat island is also used the term can be used to refer to any area that is relatively hotter than the surrounding, but generally refers to human-disturbed areas. As a population center grows, it tends to expand its area and increase its average temperature. A study has shown that heat islands can be affected by proximity to different types of land cover, so that proximity to barren land causes urban land to become hotter and proximity to vegetation makes it cooler. The main cause of the UHI effect is from the modification of land surfaces while waste heat generated by energy usage is a secondary contributor. The temperature difference is usually larger at night than during the day, and is most apparent when winds are weak, under block conditions, noticeably during the summer and winter. Urban areas usually experience the urban heat island ( UHI) effect, that is, they are significantly warmer than surrounding rural areas.
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