Relationship Between Urban Expansion Pattern And Urban Heat Island Pattern Under The Influence Of Urban Wetland

Urban area is the main areas of human activities.Livable and sustainable development of urban had been the most concerned issues for human beings.Urban heat island is a major factor affecting livable conditions,which had been studied since1980s.As one of the "three poles" of the Yangtze River Economic Belt,the middle reaches of the Yangtze River is significant.The three famous freshwater lakes,i.e,Poyang,Dongting and Honghu are the main habitats for winter migratory birds.The health and sustainable development of the middle reaches of the Yangtze River is important not only for China,but for global ecological environment and biodiversity.For the middle reaches of the Yangtze River,the relationship between the urban expansion pattern and the urban heat island pattern under the influence of wetlands has great significance for regional planning,urban livability and even the healthy development of the global ecological environment.However,former research mostly focuses on the influence of urban wetland on urban heat island.The relationship between urban expansion pattern and heat island pattern under the influence of wetland is rarely studied.In this paper,we focused on the main cities in the middle reaches of Yangtze River.Landsat 5 TM and Landsat 8 OLI/TIRS images from 1989 to 2016 were used.Thermal infrared inversion models,spatial statistical analysis and correlation analysis methods were involved to explore the relationship between urban expansion and urban heat island patterns under the influence of urban wetlands.The gravity of urban heat island(UHIG),the center of the built-up area(BUC)and the distance between UHIG and BUG were introduced in this paper.It is indicated that:(1)The distribution pattern of wetland had great influence on urban sprawl patterns.The urban expansion of Nanchang and Wuhan were orientated by wetland.Firstly urban built-up areas were distributed along the rivers,and then sprawl around the urban wetlands,finally,filled the areas between the wetlands.But for Changsha,the urban sprawl around the two rivers of Xiangjiang and Liuyang.Under the influence of wetlands distribution patterns,the built-up area expand to the southwest for Nanchang and sprawl to south for Wuhan.(2)The urban heat island pattern changed from concentration to dispersion with the influence of urban expansion.The lake wetlands outside the city were transformed from outside to inner with urban expansion,which result in the dispersion of urban heat island.(3)For urban sprawl and urban heat island patterns,great difference existed among Nanchang,Wuhan,and Changsha with the influence of wetlands.For Nanchang and Wuhan,the moving distance of BUC is much larger than that of UHIG with the influence of urban wetlands.However,little difference appeared for Changsha.(4)The cold effect of urban wetland is small,when urban sprawled uniformly.The moving distance of UHIG from BUC reflects the uniformity of urban expansion;the cooling effect of wetland could be reflected by the total distance between UHIG and wetlands.Exponential positive relationship appeared between the uniform of urban expansion and cooling effect of wetland for Nanchang and Wuhan(R~2=0.64).And linear positive correlation existed for Changsha(R~2=0.68).In other words,uniform urban expansion is not benefit for ecological environment for the main cities in the middle reaches of the Yangtze River.The above research results can provide reference for urban planning and mitigation of urban heat island effect in the middle reaches of the Yangtze River and similar areas.