The Spatio-temporal Characteristics of Impervious Surfaces and Its Land Surface Thermal Environment Effect in Great Pearl River Delta
Author:Zhang Shao Hua
In the past 40 years,the urban areas have experienced rapid expansion.As a result of urban growth,the impervious surfaces have sprawled drastically.Meantime,the forests,grasslands and framlands decreased with the expansion of impervious surfaces.Consequently,a series of urban ecoenvironment problems have occurred owing to the impervious surface expansion.Among the urban ecoenvirnoment problems,the increase in land surface temperature and urban heat island have attracted much attention from scholars.The Great Pearl River Delta(GPRD)urban agglomeration,including HongKong and Macao,is one of the three fastest growing urban agglomerations in China.Such a large-scale urban agglomeration has had a significant impact on the urban ecosystem and environment of the GPRD.Therefore,using time-serise satellite images is imperative to investigate the influence of impervious surfaces expansion on land surface thermal environment at a regional sccle.This study estimated the spatiotemporal dynamics of impervious surface areas(ISAs)in the GPRD using time series images,from 1994 to 2016.Landsat images were used to map the distribution of ISAs based on the combinational biophysical composition index(CBCI)and the bidirectional temporal filtering method.Moreover,the MOD11A2 data set was obtained from National Aeronautics and Space Administration(NASA)to investigate land surface temperature(LST)from 2000 to2016.In addition,the spatio-temporal characteristics of ISA and LST were analyzed by the landscape ecology and geospatial analysis methods.Furthermore,a series of factors that have the highest correlation with LST were extracted as the input factors.Furthermore,a simulation model of the thermal environment effect of ISA in the GPRD was built by the Support Vector Machine(SVM).After the model built,two different urban development scenarios of GPRD in next 10 years were input in the simulation model,respectively.Finaly,the results revealed the impact of ISA expansin on regional thermal environment and its influence mechanism.Moreover,the results can be used to provide decision support for the development plan of urban agglomeration and ecological city construction.The main contents and conclusions are as follows:(1)This study proposed a combinational biophysical composition index(CBCI)for the effective highlighting the four-major urban biophysical compositions.Correlation analyses were performed to estimate the relationship between the CBCI values and biophysical compositions,and the spectral discrimination index(SDI)was conducted to test the separability degree between impervious surfaces and bare soil.Moreover,normalized difference vegetation index(NDVI),normalized difference building index(NDBI),biophysical composition index(BCI),and the combinational build-up index(CBI)were utilized to perform the comparative analyses.Moreover,this research investigated the applicability of the CBCI in different spatial resolution remote sensing images.Our results indicated that the CBCI had a much closer relationship with impervious surface fraction than the other four indices and had a stronger correlation with vegetation abundances when compared with the NDVI.In addition,the CBCI had much higher SDI values than the other indices.This study proved that the CBCI was an effective index for highlighting the four-major urban biophysical compositions and had good performance for separating impervious surfaces and bare soil.(2)The results indicated that the ISA in the GPRD drastically expanded from569.23 km~2 in 1994 to 10,200.53 km~2 in 2016.The average move distance of impervious surface gravity center from 1994 to 2005 was longer than that from 2006to 2016.Moreover,the mean ratio of the major axis to minor axis of standard deviational ellipses from 1994 to 2005 was higher than that from 2006 to 2016.In addition,the value of each landscape metric rapidly increased after 2004.Therefore,the urban development pattern was rapid urban sprawl from 1994 to 2004.However,to satisfy the demand for rapid increases in the population and GDP,the urban development pattern changed to urban infill and urban consolidation due to topographic restrictions.(3)The analyzed results indicate that the daytime and nighttime average LST of GPRD were significant increased from 2000 to 2016.The daytime LST increased9.80℃with an average increase rate of 2.21%from 2000 to 2016.At the same priode,nighttime average LST increased 10.91℃with an average increase rate of 3.79%.The spatial distribution of high-temperature area has experienced obvious change.High-temperature area sprawled to a huge area,but still exsited some“cold island”.In addition,daytime thermal landscape pattern revealed the decrease trend of fragmentation,complexity and patch density and an increase trend of aggregation degree.On the contrary,the change of nighttime thermal landscape pattern dose not have an obvious trend.(4)The analysis results at regional scale indicate that the percentage of impervious surface increases by 1%,which will cause the average daytime LST to rise by 0.67℃and average nighttime LST to rise by 0.75℃.The analysis results at sub-regional scale denote that if ISA density lower than 40%or higher than 90%,which generates significant warming effect on daytime and nighttime LST.The ISA density increased by 10%,the daytime and nighttime average LST increased by 0.43℃and 0.34℃respectively.At the pixel scale,the results reveal that daytime LST and ISA have a positive and strong spaitial correlation,but the spatial correlation between nighttime LST and ISA is lower than that of daytime.Moreover,the daytime and nighttime LST have a positive and significant correlation with number of patch(NP),patch density(PD)and landscape size index(LSI).On the contrary,daytime and nighttime LSTs have a weak relationship with aggregation index(AI),area_mean(AREA_MN)and largest patch index(LPI).(5)The amount of ISA,the percentage of ISA,NP,PD and LSI were employed to build a simulation model of the thermal environment effect of ISA in GPRD via using SVM.After the model built,two different urban development scenarios of GPRD in next 10 years were input in the simulation model,respectively.The simulation results indicate that the impact of the spatial configuration of ISA on LST is greater than that of the percentage of ISA.Therefore,the spatial configuration of ISA should be reasonably planned in the future urban and regional development.Consequently,the urban and regional ecological environment can be developed in a sustainable way.