| City is the most intensive area of modern human activities.In recent years,with the acceleration of China's urbanization process,urban expansion is rapid,there are differences in urban expansion modes in different geographical regions.The environmental problems brought about by urbanization have become more and more serious,and the changes of urban heat island effect and the spatial-temporal distribution of precipitation have become important issues for urban sustainable development.Therefore,the quantitative study of urban heat island effect and the spatial-temporal distribution of precipitation can not only serve as a reference for the future study,but also provide a reference basis for urban planners and urban managers,which has important practical significance.This paper took 31 major cities in China as research objects,used the Land use/land cover type data,the MODIS land surface temperature products,the MODIS vegetation cover type products,and the CMORPH satellite precipitation data,and selected the urban expansion speed,urban expansion intensity,urban fractal dimension and Compactness,urban heat island intensity(UHII)and urban precipitation intensity ratio.This paper analyzed the expansion and morphological changes of 31 cities in China from 2000 to 2010,the spatial-temporal change of UHII and the spatial-temporal difference of urban precipitation.Finally this paper used different boundaries to extract UHII and urban precipitation ratio,analyzed the influence of urban expansion on urban heat island effect and urban precipitation.The results showed that:(1)from 2000 to 2010,31 cities in China expanded significantly,and the urban form changed.The average urban expansion rate was9.82km~2/a,the average expansion rate of cities in East China was the largest(22.08km~2/a),and that in South China was the smallest(0.64 km~2/a).In 2010,the city's fractal dimension and compactness were 1.67 and 0.15,a decrease of 0.01 compared to2000,respectively.(2)The average monthly UHII of P2000 in 31 cities was from-1.80?(November,Harbin)to 5.20?(July,Shenyang),while the average monthly UHII of P2010 was from-1.84?(February,Xi'an)to 4.68?(July,Shenyang).The average seasonal UHII of 31 cities was summer>spring>autumn>winter,and the annual average UHII decreases from 1.24? to 1.15?.Using the Fourier approximation to simulate the pattern change of the UHII in the year,it was found that there was a significant clockwise or counterclockwise change pattern,and there was a model with a cross in the middle.K-means clustering of various variation models revealed that they had significant agglomeration in several geographic regions.(3)The monthly precipitation intensity ratio of 31 cities was from 0.74 to 1.49.The average precipitation intensity ratio of 31 cities ranged from 0.83 to 1.19 in spring,from 0.93 to 1.07 in summer,from 0.74 to 1.19 in autumn and from 0.79 to 1.51 in winter.There were 10 cities less than 1 in summer,and the precipitation intensity ratio of cities in North China,Central China and South China were all greater than 1.The precipitation intensity ratio of three cities in South China had always been greater than1.The annual precipitation intensity ratio ranged from 0.85(Chengdu)to 1.21(Zhengzhou).The annual precipitation intensity ratios of Chengdu,Xining and Hefei were less than 1,while the other 28 cities were greater than 1.(4)There was a significant negative correlation between the intensity of heat island and NDVI.The greater the difference of NDVI in urban and suburb,the influence of NDVI on UHII was more obvious.Urban expansion had a positive effect on the urban heat island effect and the spatial and temporal distribution of urban precipitation.The larger the urban area,the higher the UHII and the precipitation intensity ratio.The result with 2000 boundary was smaller than that using 2010boundary statistics,which showed that the growth of urban area had a potential role in increasing urban heat island effect and urban precipitation. |
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