Landsat Thermal Infrared Data-based Spatial And Temporal Effects Of The Urban Heat Island In Nanjing

Urban heat island(UHI) effects are a kind of urban comprehensive problem,which have been recognized as one of the dominant factors raising environmentalissues in the cities and have also been one of the important topics of theenvironmental concerns at present. Nanjing, as a metropolitan located at the middleand lower reaches of Yangtze River, its urban heat island effect becomes more andmore serious due to an accelerated urbanization, which simultaneously gave rise to aseries of high heat waves in the summer seasons and an intensified environmentalpollution. Urban heat island effects in Nanjing affect the residence, production andliving environments to some extent, posing a horrible threat to the sustainabledevelopment of Nanjing. Thus, it is highly necessary to examine the heat island effectin the city. Doing so will aid in developing strategies of land uses to alleviate the heatisland intensity and to improve the living environment.Taking Nanjing as our case study, using the dense Landsat thermal observationsfrom1986to2011with a time interval of about2-3years, the land surface brightnesstemperature maps were respectively retrieved using the existing physical models,followed by an operation of normalization to the multi-temporal surface brightnesstemperature maps using a suite of pseudo invariant features points (PIF) identified toeliminate variations in sensor characteristics, atmospheric conditions, solar angle, andsensor view angle that can obscure surface change detection to make all the derivedmaps comparable directly in the current paper. Ultimately, heat island grading basedon the surface brightness temperatures was made via the means coupled with thestandard errors of the surface brightness temperatures.. The results of the studyshowed that heat island effect in the central urban areas of Najing remained stableover time, Regional conversions from low temperature to high temperature were alsowintnessed with an expansion of urban heat islands running north to south of the city.Since the1990's, heat island area has been increasingly expanded and the expansionof the heat island in the21stcentury increased faster than in the1990's. Particularly,there was a maximum of heat island area in2007and2011. When exploring thereasons causing the spatio-temporal variability of heat island, land use changes especially the impervious surfaces sprawl due to the accelerated urbanizaiton were themajor contributor to the variability. To mitigate the effects of urban heat island, somestrategies or measures were proposed, which will act as a reference for furtherresearch.