Remote Sensing Of Vegetation Dynamics And Its Impact On Urban Thermal Environment

With the rapid urban expansion,the degradation of regional eco-environment,especially urban thermal environment,has attracted global attention.As the main part of the natural productivity in urban region,vegetation plays an important role in maintaining ecological balance and improving ecological quality.Based on remote sensing and GIS techniques,this study has explored the spatiotemporal dynamics of vegetation in Fuzhou Basin and its impact on urban thermal environment,during a 25-year period from 1989 to 2014.Baesd on the comparative analysis of three vegetation classification methods including vegetation indices,maximum likelihood,and stratified classification,it is found that the stratified classification method is the best method for the extraction of vegetation information in the study area.Accordingly,vegetation extraction models using the stratified classification method were established for Landsat and Pleiades images,respectively.Results show that the area of vegetation in Fuzhou Basin decreased from 446.33 km2 in 1989 to 282.24 km2 in 2014,with a net decrease of 164.09 km2 and a decrease speed of 6.56 km2 per year.The vegetation area changed slightly from 1989 to 1996,while deseased significantly during 1996-2006 and 2006?2014.Compared to 1996?2006,the vegetation reduced speed slowed down during 2006?2014,and vegetation area in some regions even grew in this period.This is partly because of the urban growth in Fuzhou has decelerated in the late eight yeas and partly because of the re-construction of some urban areas.The single-channel algorithm was applied to retrieve land surface temperature(LST),and the EM algorithm was used to improve the spatial resolution of the four Landsat TM/TIRS thermal images from the original 120 m/100 m to 30 m.Meanwhile,the Dimidiate Pixel Model was applied to the inversion of fractional vegetation cover.The study explored the relationship between LST and fractional vegetation cover,and found that,their relationship is strongly negative.The LST wound drop with fractional vegetation cover rising.Quantitative analysis suggests that each 10%increment in fractional vegetation cover would result in the lowering of local land surface temperature approximately by 1? to 2.5 ? based on the regression models of the four study years.The result indicates that improving the fractional vegetation cover is an effective way to reduce the urban heat island effect and improve the urban thermal environment.In the investigation of the thermal environment effect of urban green parks or spaces,fourteen green spaces/parks were selected,each of which accompanied with a 300 m buffer zone.Patch characteristic parameters,fractional vegetation cover and green space types were considered into analysing the green spaces' thermal environment effect.The correlation analysis between green lands and LST shows that the vegetation fraction,shape index,and the area of green space can affect the LST of the green land and its buffer zone.The bigger the area,the more complicated the shape,the higher the fractional vegetation cover,the lower LST of the green space is,as well as more powerful of the green space's impact on the surrounding environment.The cooling distance of the green space is found to be range from 60 m to 210 m,and the cooling amplitude is 2.44?-8.57?.Green spaces with bigger area and higher fractional vegetation cover will have wider cooling range and larger cooling amplitude.