Study On Urban Heat Island Effect And Cooling Effect Of Greenland In Beijing

In this paper, Beijing is selected as study area, and there Landsat series images were selected as base data. The vegetion, building and brightness temperature were extracted, and the brightness temperature was used to express urban heat island effect. The dynamic variation rules of vegetion, building and urban heat island effect in nearly10years in Beijing were studied, and the relationship between architecture and vegetation and heat island were researched. This paper select30urban green spaces in study area. Analysis on the gradient variation of cooling effect with the distance, and the relationship between the cooling rate with the green land area and cooling effect distance were studied.The differences of cooling effect in directions of east, south, west and north of each urban green space to different construction land types, the relationship between the cooling effect of urban green space to construction land and their area and floor area ratio of the construction land were also be studied, the main conclusions are as follows:(1) Green Island is mainly distributed in north of Beijing, especially in the northwest direction, and the heat island is mainly distributed in South City. The region within5th ring road in Beijing was divided into four quadrants:southeast, southwest, northwest and northeast. And the ring road was also selected as statistical unit, the variation of urban heat island effect in Beijing in nearly ten years were studied at the angle of spatial orientation and circle structure. The result show that the intensity of heat island in Beijing as a whole is weakened.(2) In nearly ten years, the urban green area is gradually reduced. Urban green space in study area has decreased by nearly5,000hectares from2004to2013, and urban green space within each ring road is also decreasing. The area farther away from the center, the more area reduced. Urban construction land area increased by more than7000hectares, and the increased construction land is mainly distributed in the vast area of from3rd ring road to5th ring road.(3) Urban green space has the function of easing urban heat island effect, and the distance of cooling effect of Beijing urban green is in the interview of100-200m. The distance of urban green space has an increased trend with the raise of ring road, and the farther away from city center, the greater the distance of green space cooling effect is. It is the logarithmic relation between Green land area and cooling effect scope. Within a certain range, the cooling effect of green space increase with the increase of the area, but the size tends to be smaller and smaller.(4) Among the30selected urban green space, the largest cooling rate of all green space is about1℃, and there is no obvious correlation between area of green space and cooling rate. Among the30selected urban green space, the green space with the largest cooling rate is Nianzhuang green space, and the value is1.94℃; the green space with the minimal cooling rate is Wangjing green space, and the value is only0.4℃. With the ring road extrapolation, the average cooling rate in the corresponding area of urban green space is increased, that is to say, the farther away from the city center, the more obvious of the cooling effect of urban green space is.(5) Urban green cooling effect with the gradient changes of the type of distance can be divided into parabolic, logarithm change and uniform change. The reasons of presenting different types related to the surrounding construction land layout.(6) In the view of cooling range of green space work on four direction building land, the descending order of Greenland’s cooling effect on construction land is west> South> North> East. The order from large to small of the cooling rate that green land to construction land nearby is:Traffic land>Residence land> Warehousing land> Public administration and public services land> Utilities land> Commercial land.(7) In this study, the regression analysis between cooling rate of greenland and the area ratio between greenland and construction land, and floor area ratio were carried out. The results show that there has a significant positive correlation between cooling rate of greenland and the area ratio between greenland and construction land, and there has a significant negitive correlation between cooling rate of greenland and the floor area ratio of construction land. A relational model was built by the comprehensive analysis, and the optimal layout of construction land could be determined from the angle of alleviating urban heat island.The suitable order of direction that surrounding greenland for arranging a large area of construction land is East> South> West> North. The suitable order of direction that surrounding greenland for arranging high floor area ratio of construction land is East> South> West> North.