| Urban heat island impact on the urban ecological environment. The previous study on heat island effect in Beijing area usually used the meteorological information which has a low spatial resolution. The related research using satellite data, because of the large amount of data and complex process (using of a scene or view data representative of a longer period of time) has a low time resolution and poor representation. In the usual sense of the urban heat island (UHI) refers to the air temperature difference between urban and rural areas, so we need to obtain a high precision of level distribution of surface air temperature by the remote sensing data of land surface temperature and the air temperature by observation stations.In this paper, the surface air temperature inversion model of city and non-city is established by statistical regression and using the land surface temperature data of MODIS satellite inversion data of 2003-2012 years combined meteorological observation air temperature in the same period, in consideration of the influence of different land cover types. The surface air temperature by inversion retains the characteristics of high precision and good time continuity as observation data, but also has the advantages of high spatial resolution as satellite data. Based on the inversed data, the temporal and spatial distribution, the causes and mitigation measures of urban heat island effect in Beijing area is analyzed. The main conclusions are as follows:(1)The surface air temperature in Beijing area is influenced by latitude, altitude and underlying surface types. The spatial distribution of temperature is high in south and east, and low in north and west. During the day, the temperature of the high value areas are mainly located in the southeastern plain area, where mainly is city and arable land, and the temperature of low value areas are mainly located in the western and northern hilly areas, where is covered by dense vegetation. The urban heat island intensity is 4.32℃, and heat island warming is 0.5℃. At night, because of the larger temperature difference of the cereal crops between day and night, the 0 line of the average surface air temperature move toward the northwest passage. The northern part of Miyun and middle and western part of Yanqing County is in the higher altitude, so the surface coverage of the cereal crops decline even more at night, appearing at a low value area of temperature. While the average surface air temperature in the city is still the highest, heat island intensity is 3.74℃,heat island warming is 0.42℃. The urban heat island effect is obvious during the day and night, and the distribution of heat island is wide at night and intensive during the day. City heat island is flaky divergent with Beijing city as the center, other counties scattered heat island in the town.(2)Due to seasonal changes in the intensity of solar radiation in Beijing area, the average surface air temperature in summer is the highest, and lowest in winter, spring and autumn ranged between two. While the solar radiation is in the same conditions, the difference of the nature of the underlying surface also causes significant differences in the spatial distribution of ground temperature, so the heat island effect has obvious seasonal variation. The specific performance:During the day, the surface air temperature is mainly affected by the effect of solar radiation. As the sun elevation angle is highest of the year in summer, city dense building reflected little solar radiation in summer, and the city buildings use more air conditioning, release a lot of heat source of human, the heat island intensity is highest in the summer (5.26℃). In winter, the sun elevation angle is lowest of the year, and dense building shadow is easy to form, the shortwave radiation is reduced, the heat island intensity is lowest in the winter (5.26℃). The heat island intensities of Spring and autumn are 3.76℃ and 3.34℃. At night, the surface temperature is mainly affected by the wave of underlying surface and anthropogenic heat radiation effect. Because the heating period in Beijing area (11-3) with coal as the main fuel, a large number of coal combustion adds to anthropogenic heat generated directly, but also indirectly increases the content of greenhouse gas (CO2) and the more serious pollution at night. The heat island intensity in winter is the highest (3.92℃). The heat island intensities of spring and summer are 3.76 and 3.72℃,and the heat island intensity is minimum (3.38 C) in autumn.(3)Between ten years from 2003 to 2012, the temperature of high value area is located in Beijing City, and the area is increasing year by year, the heat island effect is prominent. The surface air temperature in summer has increased year by year, the rate of change is 0.056℃/year, and it is decreasing year by year in winter, the rate of change is -0.237℃/year, while the average annual change showed a trend of decrease of-0.100℃/year. Because of the influence of human factors, the temperature of urban decreases slowly, and the temperature of non-urban decreases quickly, thus intensity of heat island and heat island warming appears upward trend of 0.018℃/year, and 0.001℃/year, the rate of the change that is urban heat island effect has been increasing year by year.Through this study, due to the impact of the Beijing area of urban geographical environment, surface properties and anthropogenic heat emission factors, urban heat island effect is significant. Over the past 10 years, the cold winter and hot summer and the trend of city heat island intensity are increasing, it brings the adverse impact on the energy consumption and the health of residents.The problem of city planning, energy optimization and environmental protection reasonable need to be solved. |
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