Landsat Evaluation of Land Cover Composition and its Impacts on Urban Thermal Environment: A Case Study on the Fast-growing Shanghai Metropolitan Area from 2000 to 2015
Land surface temperature (LST) is an important yardstick of evaluating urban thermal effect. Researches on how the LST spatiotemporally respond to land use/cover (LUC) change can better understand the mechanism of urban heat island (UHI) formation, quantitatively examine the thermal contribution of urban biophysical components, and further ease the negative influence of accelerating urbanization. Using Landsat data, this study attempts to evaluate the spatial changes in land cover and its impacts on the urban thermal environment in the fastgrowing Shanghai metropolitan area (SMA). Based on the results of LUC classification and LST retrieval, we estimated the contribution proportion of different land cover on the thermal environment. Then, we performed the spatial concentric zone analysis and profile analysis according to the, urban-rural gradient theory. During the years from 2000 to 2015, the changes in observed values and trend of UHI over time, were highly co-related with the urban expansion of SMA. The results indicated that the UHI zone was gradually expanding between these 15 years, whereas the UHI intensity of the inner city in SMA was declining. The relative difference of thermal effect between the downtown and the outskirts was also decreasing. Additionally, we identified that the land cover composition has notably affected the urban thermal environment. In SMA, the substantial expansion of impervious surface (IS) has heavily influenced the urban thermal effect; in contrast, the spatial adjustments of urban greenspace infrastructure including vegetation and water, effectively relieve UHI phenomenon and enhance the effect of urban greenspace cooling island (UGCI). The finding is expected to provide references and clues for the decision-makers for optimizing and creating appropriate sustainable urban development strategies.