Dynamic Monitoring And Analysis On The Thermal Environmental Effects Of Typical Urban Heat Island Cities

The urban heat island(UHI)effect has a strong negative impact on the urban ecological environment and human’s health.Therefore,the study of UHI effect is of great significance to protect human’s healthy,reduce energy consumption and improve living environment.This research has chosen two typical UHI cities,Fuzhou and Nanjing as target regions,and used four Lansat images to discuss the thermal environment changes and the factors causing dynamic changes of UHI of the two cities,respectively,in the period between 2000 and 2013.Based on the several thematic indices,different land cover types were classified.The image-based method(IB)was chosen to retrieve the land surface temperature(LST)from thermal infrared images.Then the thermal image’s spatial resolution was sharpened to 30 m with the assistance of the sub-pixel unmixing method.The LST was subdivided into seven levels by using normalizing and density slicing method.According to the spatial distribution of the LST,three of seven levels(levels 5 to 7)were used to study UHI.The changes of urban thermal environment in Fuzhou and Nanjing were compared by combining Urban Heat Island Intensity(UHII),Urban-Heat-Island Ratio(URI),the change of LST level and the landscape distribution pattern.The result indicates that the UHII in Fuzhou has risen from 5.93℃ to 6.56℃ and the URI has risen from 0.288 to 0.482.As for Nanjing,the UHII has reduced from 5.24℃ to 4.38℃,and the URI has increased from 0.289 to 0.353.This suggested that the UHI effect in Fuzhou was greatly enhanced in the 13-study years,while the UHI of Nanjing was mitigated.Furthermore,the LST amplitude of heating up regions of Fuzhou was greater than Nanjing,while the LST amplitude of cooling regions was lower.In terms of the landscape distribution pattern,the UHI in Fuzhou and Nanjing were expanded in group.The distribution of Fuzhou’s UHI patches of a same type was more concentrated than those of Nanjing.The patches in Nanjing were mixed and gathered with in different types.In order to investigate the factors that had caused the different changes of thermal environment of Fuzhou and Nanjing,several different thematic indices were used to study the relationships between three land cover types(built-up,vegetation and water)and LST.The results showed that there was a positively correlation between built-up land and LST,but vegetation had a negative correlation with LST,so did water.The influence that built-up land had on LST was greater than the influence of water and vegetation.In addition,the change of urban thermal environment was affected by natural conditions(such as the space of urban expansion and ventilation condition),population(such as population density,and energy consumption)and related policies(such as urban expansion strategies,and ecological planning).Overall,most of the factors have caused the urban thermal environment of Fuzhou to become worse.On the other hand,UHI effect of Nanjing was conversely improved.