Study On Spatial And Temporal Variation Of Thermal Environment And Its Influencing Factors Over Beijing-Tianjin-Tangshan Urban Group

With change of global climate and development of urbanization, urban thermal environment has changed significantly. The study of spatial and temporal variation of thermal environment and its influencing factors over J-J-T urban group, can provide the basis for assessment of climate change, influence of urbanization on this area and improvement of the urban ecological environment. Based on meteorological data of Beijing from 1960 to 2003, social economic data of Beijing from 1982 to 2003, combined with the MODIS LST(Land Surface Temperature),NDVI(Normalized Difference Vegetation Index) and land cover type products from 2002 to 2009, this paper analyzed dynamic change of the thermal environment distribution of different scales and its influencing factors.As to the typical city's UHI(Urban Heat Island), the main conclusions are as follows:(1) The UHI intensity in Beijing shows an increasing trend with a 0.23℃/10a increasing speed. The obviously strong daily UHI occurs at nighttime, whereas a week daily UHI appears at daytime. Seasonally, the daily UHI effect is obvious in winter compared with other seasons, the UHI reached 4℃at night and 1.8℃during the day. The amplitude between day and night is the largest in winter which is 3.1℃and the smallest in summer, which is 1.6℃.(2) There is a negative correlation between the UHI and wind speed in Beijing region(R=-0.559), and declining wind speed led to UHI intensity increase. With the increase of population, GDP, electricity consumption and the number of vehicles, the urban heat island effect presents a linear or log growth trend, and there is an significant correlation between UHI and GDP(R=0.73).As to the J-J-T urban group's thermal environment, the main conclusions are as follows:(1) By analysis of thermal environment of J-J-T urban group, we can conclude that LST at day and night are higher in urban than in the surrounding rural areas. In a word, it has an obvious UHI effect in J-J-T area. The urban group and its surrounding towns formed a large "heat island group", and LST reached 34℃. The UHI intensity is the largest in winter, Beijing reached 3.54℃, Tianjin reached 4.91℃and Tangshan reached 0.80℃.The shape, size, position of the heat island is consistent with the urban area. Due to the different surface constituent materials and the variation of locations, the distribution of high temperature value is scattered, especially in winter. (2) By analyzing characteristics of thermal environment of different seasons from 2002 to 2009, we can conclude that the distribution and variation of the thermal fields are different according to the different seasons. The thermal field in urban districts changes little, and distribution of UHI intensity in the suburbs of the city presents a gradually increasing trend.(3) The distribution of NDVI shows significant seasonal difference. For all the land types, NDVI and LST show a negative correlation. There is an obvious negative correlation between NDVI and LST in summer(R=-0.59), which indicates that woodland can greatly reduce the LST. From the urban center to the suburbs, with the increase of vegetation cover, the LST decreases constantly. The LST of urban is higher than the suburbs and presents significant UHI effect.