Evolution Of Urban Heat Island Effect In Xining From Landsat Satellites

The rapid urbanization process not only has greatly changed the underlying surface characteristics of the city,but bring about the daily emissions from urban construction,transportation,industrial production and daily life of residents constantly increasing too.The urban thermal environment is becoming more and more obvious,and the "urban heat island" effect has attracted much attention.This paper taking Xining city as a case study area,which located in a river valley with severe human disturbance,first of all,using the Landsat images in recent 30 years from 1987 to 2015,the boundary of built-up area for Xining city was extracted and its dynamic changes were studied;Secondly,12 years images representing winter and summer during the period of 1987-2015 were selected,and then the surface temperature of each year image was estimated based on the single window algorithm.As well temporal,spatial evolution characteristics of the urban land surface temperature and heat island intensity are quantitatively analyzed.Thirdly,the influencing factors of urban heat island effect were analyzed,and the regression analysis of urban heat island intensity with its influencing factors was carried out.The multiple regression equations of heat island intensity in summer and winter were obtained.Finally,it puts forward the regulation mechanism and mitigation measures of urban heat island effect in the process of urbanization.The conclusions are as follows:(1)The dynamic analysis of the built-up area of Xining shows that: From 1987 to 2000,the urban development of Xining is slow,the built-up area is mainly located in the center of the city.From 2000 to 2003,the built-up area significantly increased,in addition to the downtown center,there are small pieces of built-up area in Bridge Town Datong County,Chengguan Town Huangyuan County and Lushaer Town Huangzhong County.But these built up areas are disconnected.From 2003 to 2013,with the urban area as the origin,the built-up areas expanded rapidly in the four directions of the East,West,South and North,and small built-up areas continued to emerge.By 2015,the Xining built-up area had become a cross shaped connected area,the west to Chengguan Town,north to Qiaotou Town,South to Lushaer Town,east to the Economic Development Zone..(2)The temporal and spatial evolution characteristics of surface temperature in Xining show that: During the summer after 1995,there is an obvious suburban temperature difference.From 2000 to 2003,the urban heat source increased obviously,but the distribution was scattered.Urban centres,new urban areas,industrial areas and bare land are characterized by high temperature or sub high temperature zones.From 2003 to 2011,the area of sub distribution of sub high temperature and high temperature gradually increased,and merged into a larger area of high temperature.By 2011,the whole urban area was in the sub high temperature area.In 2015,except the urban areas,there were sub high temperature zones along the traffic routes from the urban areas to the surrounding towns,and the new urban areas and the industrial areas were in the high temperature zone.During the winter months,from 1989 onwards,the urban areas were represented as "cold island",and along with the urban construction and development,the cold island area expanded in four directions: the east,the west,the south and the north.The trend of variation is consistent with the trend of built-up area.Before 2000,the suburbs,valleys and shallow mountain zone has a large areas of the high temperature and high temperature.After 2000,especially in 2006,the area of high temperature and sub high temperature gradually decreased.By 2015,most of them were converted into middle temperature zone.Only a few high temperature and sub high temperature zones existed.(3)The quantitative analysis of Xining urban heat island effect showed that: The change of heat island area in summer and winter in Xining was not obvious before 2000.After 2000,the area of heat island area increased rapidly,and the area of heat island area was the largest in 2003.After 2003,the area of heat island gradually declined.The intensity of urban heat island effect is divided into three periods in time.From 1987 to 2000,the heat island effect increased slowly,and it was rapidly increased from 2000 to 2003.The heat island effect gradually declined from 2003 to 2011.From 2011 to 2015,the change of heat island effect is not obvious.(4)During the summer days,the heat island intensity was positively related to the number of vehicles in urban areas,built-up area,NDBI mean and population,and the heat island intensity was negatively correlated with urban greening rate,urban NDVI mean and BCI mean in.During the winter,the heat island intensity of Xining city was positively related to the urban greening rate,NDVI mean,NDBI mean and BCI mean,and negatively correlated with the number of urban vehicles and built-up area,and the correlation with the population was not obvious.Acorrding to this basis,the regression analysis of heat island intensity HI(T)of each index and Xining city was carried out,and the regression equation of heat island intensity in winter and summer was obtained.