What Is the Heat Island Effect?

The Urban Heat Island Effect refers to the phenomenon that the temperature of an area is higher than the surrounding area. It is expressed by the temperature difference (ie, the intensity of the heat island) at two representative measurement points. There are two types of urban heat island effect and the Qinghai-Tibet Plateau heat island effect.

Due to dense urban buildings, asphalt roads and cement pavements have greater heat absorption and smaller specific heat capacity than soil and vegetation in the suburbs, causing urban areas to heat up faster and radiate a lot to the surroundings and the atmosphere, causing the same The temperature in urban areas is generally higher than the surrounding suburbs. High-temperature areas are surrounded by low-temperature suburbs.

English name: Urban Heat Island Effect, UHI for short (not thermal conductivity effect)

One of the most significant characteristics of urban climate is the heat island effect. Humans have long discovered that the atmospheric environment of cities has different characteristics from those of rural and mountainous areas. The Englishman Lake Howard first wrote in 1833 that the temperature in the center of London was higher than that in the suburbs. ^[1]

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(1) Protect and increase the area of green space and water in urban areas. Because the water body and green space in the urban area play a considerable role in reducing the urban heat island effect in summer.

(2) The intensity of urban heat islands will increase with the development of cities. Therefore, while controlling urban development, it is also necessary to control urban population density and building density. Because high-density areas are also high-density areas for buildings and high-energy consumption areas, high-temperature areas are often formed.

(3) If Beijing is located in the middle of the plain, it is surrounded by mountains on three sides. Due to the influence of the valley wind, the south-north wind direction prevails. Northerly winds at night and more southerly winds during the day. Therefore, when expanding a new urban area or rebuilding an old urban area, the streets running from north to south should be appropriately widened to enhance urban ventilation and reduce the intensity of urban heat islands.

(4) Reducing the release of man-made heat, and changing civilian coal to liquefied gas and natural gas as much as possible, and expanding the heating area are also fundamental countermeasures.

Because the specific heat of water is greater than the specific heat of concrete, under the condition of absorbing the same heat, the temperature rises between the two are different and a temperature difference is formed. This inevitably increases the circulation speed of the thermal circulation. The water system around the city played a secondary cooling role, so that the temperature in the urban area would not be too high, and the purpose of preventing the urban heat island effect was achieved.

In addition, dense urban population is also one of the important reasons for the formation of the heat island effect. Therefore, in the planning of new cities in the future, it can be considered that only the central government and municipal government, tourism, finance and other departments should be retained in the city center, and the remaining departments should be relocated to satellite cities, and then connect the satellite cities through the metro ring.

(5) The city is densely populated and has less green area, so more trees should be planted.

(6) It is also necessary to control factory emissions.

(7) Compensation for artificial evaporation: The primary solution to urban thermal pollution is to increase the amount of evaporation. Constrained by urban installation conditions, the use of spray systems is an efficient and economical method. When the evaporation is 0.05g / sm (11 hours of spraying during the day is equivalent to 2mm rainfall), the average temperature of the atmosphere drops to 7 ° C.