Study On Urban Landscape Pattern And The Thermal Environment Effect In Xi’an

With the development of economy and acceleration of urbanization,the surface covered by natural vegetation is gradually replaced by impervious surface such as cement and asphalt, which makes the thermal properties of underlying surface change, and then affect the urban thermal environment. Besides,population and the number of industrial and mining enterprises have risen sharply.the people and enterprises emission a lot of waste heat and exhaust gas when they live and product daily.As a result, the urban ecological environment is seriously destructed.Xi’an as the starting point of the new Silk Road gradually moves towards the international metropolis. Along with the "one way" strategy,the city scale unceasingly expands,but the thermal environment worsens. The twenty-first session of the United Nations Climate Change Conference set the temperature rise no more than 2℃.Therefore the research of Xi’an city heat environment has the vital significance.This study contrasted the ground observation method,thermal infrared remote sensing technology, numerical simulation of space,which of studying the city thermal environment and choose the the method of remote sensing to monitor the thermal environment of Xi’an City.By comparing the advantages and disadvantages of the existing remote sensing data,this paper selected TM/ETM+ and OLI from 2000 to2014,and then corrected,cut and enhanced them.Otherwise, the radiative transfer equation method was used to retrieve land surface temperature.The paper also analyzed the temporal and spatial variation of heat environment in Xi’an City based on the graph of land surface temperature which came from normalized treatment and divided into five zones for the strong heat island area, island area, middle area, green area and strong green area of the land surface temperature by using the method of equidistant partition.Then,the paper calculated the thermal landscape pattern index by using software of Fragstats and analyzed the evolution of the thermal landscape pattern. Finally, the paper analyzed qualitatively the natural and man-made factors affecting the thermal environment of Xi’an city and put forward the improvement measures from the aspects of rational planning of urban construction, control of urban heat source and pollutant emissions.In this research,the main results have been concluded:(1)In Xi’an,urban thermal field expanded from the city center to the periphery and distributed the whole city,which change form scattered points to sheet and then to the variation of diffusion in the space form.From 2000 to 2007,strong heat island area and heat island area increased markedly,but middle area and green area reduced and they shared as high as 90% of the total area.From 2007 to 2014,strong heat island area and heat island area continued to increase,especially heat island area which increased from 6.02% to 17.04%.Green area reduced from 65.83% to 42.25%.(2)the green area was the dominant patch in 2000 and the proportion of it was much higher than other area,but the fragmentation degree was higher.It and the middle area of circumference of fractal dimension were higher,illustrating that their patch shape was complex,and high degree of differentiation, while the other three types of landscape shape were more regular than it;In 2007 the ratio of the green area was55.54%, still was the advantages of plaques, the shape of green island area and heat island area were more complex than other areas,the degree of fragmentation about middle area and green area was higher than other areas.Thermal landscape differentiation was more serious;In 2014 the ratio of the the middle area was35.57%,which became the dominant patch.The change of heat island area, middle area and the green area was strong and the degree of fragmentation was higher.The middle area fragmentation degree was higher, the edge density and patch density showed a consistent change rule,in other words,the middle area > heat island area >green area > strong heat island area > strong green area,which showed green area gradually reduced, and turned to heat island area and middle area.(3)The paper analyzed the variation of landscape pattern index.Then,revealed dynamic evolve process of the urban heat island.As the time goes,it showed that heat landscape pattern dramatically changed and the degree of fragmentation increased.(4)In view of the Xi’an thermal environment distribution and evolution law,this paper considered from three aspects of urban planning, control of the three urban heat and pollutant emissions to improve the thermal environment.Firstly,Xi’an should reasonably plan urban development and control urban population.Secondly,it should increase the amount of urban greening,for example,develop three-dimensional green.Besides protecting the original water system and vigorously putting up water projects should be considered.New energy,new technology and new equipment should be applied universally.The last but not least,it should promote production and lifestyle of green energy.In addition it must effectively control industrial heat source andartificial heat source of "three wastes" emissions.All of them play active roles for improving thermal environment of Xi’an.There are 30 figures, 7 tables, 90 references in this article.