The Impact Of Land Use/cover Change On Urban Thermal Environment

Urbanization is an inevitable trend for social development.In the 21 st century,with the continuous acceleration of urbanization,the land use/cover of domestic cities is undergoing drastic changes,such as a decrease in arable land and an increase in urban construction land.These changes have led to changes in the urban thermal environment.Studying the spatiotemporal evolution characteristics and laws of urban land use/cover change and thermal environment,exploring the process and impact mechanism of land use/cover change and thermal environment change,has important practical significance for regional ecological environment protection and urban sustainable development.In this paper,eight cities,including Beijing and Shenyang,are taken as research areas.Based on Landsat remote sensing images and land use data,the influence of land use/cover change on urban thermal environment is analyzed by introducing heat island intensity index,thermal effect contribution index,thermal unit weight index and regional thermal unit weight index through land use dynamic attitude,land use transfer matrix,surface temperature inversion and thermal class classification.The main conclusions are as follows:(1)During 2000-2020,the land use/cover change of the cities in the study area showed that the construction land gradually increased,while the green land(cultivated land,woodland and grassland)gradually decreased,and other land use/cover types showed different behaviors in different cities.In land use/cover change,construction land and cultivated land are the most obvious in terms of the speed and range of change,and the growth of construction land in cities is particularly prominent.From 2000 to 2020,in the change of land use/cover transfer,the number of cultivated land transferred out and the number of construction land transferred in are the largest,and cultivated land is the main contributor to the increase of construction land,and urban expansion has occupied a part of cultivated land.(2)The distribution of high temperature areas in the cities in the study area is relatively concentrated,while the distribution of sub-high temperature areas is wider and relatively scattered than that of high temperature areas.Research has found that the sub high temperature areas and high temperature areas in cities are mainly distributed in construction land and arable land;Low temperature and sub moderate temperature areas are mainly distributed in forest and water areas,as well as in farmland and grasslands far from the city center.In the study area,the heat island intensity of Beijing,Zhengzhou,Guiyang and Guangzhou has decreased,while that of Shenyang,Xi ’an,Shanghai and Wuhan has increased,which shows that urban development does not necessarily lead to the deterioration of the thermal environment,and reasonable urban planning can improve the urban thermal environment.(3)In the cities of the research area,the distribution of cultivated land in the thermal class classification is mainly in the sub medium temperature zone,medium temperature zone,and sub high temperature zone;Construction land is mainly distributed in sub-high temperature area and high temperature area;Most of the forest land is mainly distributed in sub-middle temperature zone,medium temperature zone and sub-high temperature zone;The middle temperature area is the most distributed in grassland;The distribution of water areas is mainly low temperature area,sub-medium temperature area and medium temperature area;The proportion of unused land in the city is very small,and its law is not obvious.From the thermal effect contribution index,the contribution of construction land and cultivated land is the largest in all the cities studied,and the contribution of construction land is rising,while the contribution of cultivated land is declining.From the thermal unit weight index,the thermal unit weight index of construction land is the highest.Judging from the weight index of regional thermal unit,the weight index of regional thermal unit of construction land or cultivated land is the highest,and the influence of construction land on urban regional thermal environment is gradually expanding.(4)Construction land and cultivated land are the two land types that have the greatest impact on the urban thermal environment in the cities in the study area.In Beijing and Shanghai,the land type that has the greatest influence on the change of thermal environment has changed from cultivated land to construction land;Among the other six cities,cultivated land has the greatest influence on the change of thermal environment,followed by construction land.The results show that with the continuous development of the city,the influence of construction land on the change of urban thermal environment will exceed that of cultivated land and become the biggest land-type factor affecting the urban thermal environment.The construction land and cultivated land in the study area are closely related to the urban thermal environment.In the future urban development process,we should first pay attention to the planning of construction land and not blindly expand construction land.