Why is the temperature in the city higher than that in the suburbs? Answer with geographical knowledge. Urgent need!

On a clear and windless summer day, the ground temperature on the island is higher than that of the surrounding sea water, thus forming sea breeze circulation and cumulus convection on the island, which is the performance of the ocean heat island effect. In recent years, urban population is concentrated, industry is developed, traffic congestion and air pollution are serious, and buildings in cities are mostly stone and concrete, with high thermal conductivity and heat capacity. In addition, the building itself can block or weaken the wind, which can make the annual average temperature of the city 2 degrees Celsius higher than that of the suburbs, or even more. In the spatial distribution of temperature, the city is like a warm island, thus forming the urban heat island effect. The heat island effect is a comprehensive phenomenon of microclimate change caused by people changing the urban surface, which is most obvious in winter and more obvious at night than during the day. This is one of the most obvious features of urban climate.

Climate is the external cause of urban heat island effect, while urbanization is the internal cause of urban heat island formation. It is generally believed that there are three causes of heat island: first, the surface properties of cities and suburbs are different, and the thermal properties are quite different. The urban area has low reflectivity, more heat absorption, less evaporation heat consumption, fast heat conduction and slow radiation heat loss, just the opposite in the suburbs; Second, the man-made heat emitted by urban areas is greater than that in suburbs; Third, the urban air pollution concentration is high, and there are many aerosol particles, which plays a role in heat preservation to a certain extent.

Air pollution plays a very complicated and special role in urban heat island effect. Air pollutants from industrial production, transportation and daily life are especially concentrated in urban areas. They cover the city like a thick blanket. During the day, it greatly weakens the direct radiation of the sun, slows down the temperature rise in urban areas, and sometimes produces the "cold island" effect in cities. At night, it will greatly reduce the heat loss caused by effective long-wave radiation on the urban surface, play a role in heat preservation, make the city "cool" slower than the suburbs, and form a night heat island phenomenon. Starting from urban meteorological planning and design, we should consider:

(1) It is necessary to protect and increase the urban green space and water area. Because the urban water bodies and green spaces have a considerable role in weakening the urban heat island effect in summer.

(2) The intensity of urban heat island increases with the development of the city. While controlling the development of the city, we should also control the population density and building density of the city. Because densely populated areas are also high density areas and high energy consumption areas of buildings, high temperature areas often form.

(3) If Beijing is located in the middle of the plain and surrounded by mountains on three sides. Due to the influence of mountain valley wind, the wind direction from south to north prevails. North at night and south during the day. Therefore, when expanding the new urban area or rebuilding the old urban area, the north-south streets should be appropriately widened to strengthen urban ventilation and reduce the intensity of urban heat island.

(4) Reducing man-made heat release, changing civil coal into liquefied gas and natural gas as far as possible, and expanding heating area are also fundamental countermeasures.

Urbanheatisleffect refers to the phenomenon that the temperature in the city is obviously higher than that in the peripheral suburbs. On the near-surface temperature map, the temperature in the suburbs does not change much, while the urban area is a high temperature area, just like an island protruding from the sea. Because this island represents a high-temperature urban area, it is vividly called an urban heat island. The urban heat island effect makes the annual average temperature of the city 65438 0℃ higher than that of the suburbs, or even more. In summer, the temperature in some parts of the city is sometimes more than 6℃ higher than that in the suburbs. In addition, the dense and tall buildings in the city block the airflow and reduce the wind speed in the city. Due to the urban heat island effect, the urban and suburban areas have formed a thermal circulation that is opposite day and night.

In recent years, with the rapid development of urban construction, the urban heat island effect has become more and more obvious. The main reasons for the formation of urban heat island are as follows:

Firstly, it is influenced by the characteristics of urban underlying surface. There are a large number of artificial structures in cities, such as concrete, asphalt pavement and various building walls, which change the thermal properties of the underlying surface. These artificial structures absorb heat quickly and have small heat capacity. Under the same solar radiation conditions, they heat up faster than the natural underlying surfaces (green space, water surface, etc.). ), so their surface temperature is obviously higher than the natural underlying surface.

Another main reason is the influence of man-made heat source. Factory production, transportation and residents' life all need to burn all kinds of fuels, and a lot of heat is emitted every day.

In addition, the reduction of green space, trees and water bodies in cities is also a major reason. With the development of urbanization and the increase of urban population, the number of buildings, squares and roads in cities has increased greatly, but the number of green spaces and water bodies has decreased accordingly, and the ability to alleviate the heat island effect has weakened.

Of course, air pollution in cities is also an important reason. Motor vehicles, industrial production and urban residents' life have produced a large number of emissions such as nitrogen oxides, carbon dioxide and dust. These substances will absorb the thermal radiation of the underlying surface, produce the greenhouse effect, and further heat up the atmosphere.

In principle, the urban heat island effect may occur all year round. However, the biggest influence on residents' life and consumption is the heat island effect in high temperature weather in summer. In order to reduce the indoor temperature and make the indoor air circulate, people use air conditioners, electric fans and other electrical appliances, which consume a lot of electricity. For example, at present, the electricity consumption of the United States 1/6 is used for refrigeration, so it needs to pay $40 billion in electricity bills every year. High temperature weather also has adverse effects on human health. Relevant research shows that people will feel uncomfortable when the ambient temperature is higher than 28℃. No matter how high the temperature is, it is easy to cause symptoms such as irritability, heatstroke and mental disorder; If the temperature continues to be higher than 34℃, it can also lead to a series of diseases, especially cardiovascular and cerebrovascular diseases and respiratory diseases, and the mortality rate will increase significantly. In addition, the temperature rise will accelerate photochemical reaction, increase the ozone concentration in the near-surface atmosphere, and affect human health.