Change Analysis On Land Use And Key Land Surface Parameters In The Three Gorges Reservoir Catchment Based On Google Earth Engine

Since the 1990s,the research on land use and land cover change(LUCC)has been strengthened in the field of global changes.LUCC is closely related to global environmental change,and also highly related to the sustainable development of the national or regional development strategy.The Three Gorges Project(TGP)was officially started in 1994 and completed in 2009.In 2010,the water level in the Three Gorges Reservoir Catchment(TGRC)reached to 175 meters.During the construction of the reservoir catchment,due to the strong influence of human factors,the land use change(LUC)in the catchment was intense.LUC would have direct impacts on vegetation cover,land surface temperature(LST),and albedo.Therefore,it is of great significance to study the spatiotemporal dynamic trend of LUC and related changes of land surface parameters to deeply understand the land use and ecological environment of the TGRC.Taking the TGRC as the research area,this study used the land cover classification data provided by the European Space Agency(ESA)to study the land use status and changes in the TGRC in 2000,2005,2010 and 2015.The Moderate Resolution Imaging Spectroradiometer(MODIS)time series products archived in Google Earth Engine(GEE)platform,such as Normalized Difference Vegetation Index(NDVI),LST and albedo were employed to study the spatial distribution characteristics and temporal variation trends of vegetation cover,LST and albedo in the TGRC from 2000 to 2015.Then,the changes in vegetation cover,LST,and albedo were studied and analyzed at interannual scale and seasonal scale.In addition,intraannual monthly analysis was given to vegetation coverage.Meanwhile,the land use data of the four periods of 2000,2005,2010 and 2015 in the reservoir catchment were overlaid and analyzed statistically with the results of land surface parameters in the corresponding years,to obtain the variation rules of land surface parameters corresponding to different land use types,as well as the different land surface parameters change trends corresponding to a same land use type.At the same time,the correlation coefficients between vegetation cover and LST and albedo was analyzed to obtain the correlation degree of them.Finally,the changes of land use and the land surface parameters are studied in some specific regions.Through the above studies,it was found that the land use types in the TGRC from2000 to 2015 were mainly cultivated land and forest,and the land use changes were mainly manifested in the decrease of cultivated land,grassland and shrubland,which decreased by 1514.79 km~2,32.4 km~2,and 391.5 km~2,respectively.The increased areas of forest,waterbody,and the artificial surface were 1247.04km~2,22.95km~2,and668.7km~2,respectively.Cultivated land is mainly distributed in the northwest of Kufu(belly of the TGRC)and Kuwei(tail of the TGRC).Forest is mainly distributed in the Kushou(head of the TGRC)and the northeast of Kufu.Artificial surface is mainly distributed in Kushou and Kuwei,as such Yichang City,Chongqing City and its surrounding Districts and Counties,and the Wanzhou District located in Kufu.Grassland and shrubland are scattered in the reservoir catchment.The comprehensive index of land use degree in the TGRC shows that it decreased from 2000 to 2005 and increased from 2005 to 2015,which indicating that the development degree of land resources in the reservoir catchment is gradually improving and the land utilization rate is increasing in recent years.The transfer matrix of land use found that the change of land use types were mainly concentrated in cultivated land,forest,shrubland and artificial surface.The increase of artificial surface due to transferred from the cultivated land,while the increase of forest due to transferred from cultivated land and shrubland.Cultivated land,forest,and grassland are transferred to waterbody.In addition,the change of grassland is less obvious,because of the total amount of grassland is small.From 2000 to 2015,the Seasonally Integrated Normalized Difference Vegetation Index(SINDVI)presents a rising trend,grew by an average of 2.89 in the study area.At the seasonal scale,the SINDVI showed an increasing trend in the four seasons,but the magnitude and trend of the increase were different,and the maximum value appeared in 2015.At the monthly scale,the SINDVI showed a single-peak curve,and the monthly mean SINDVI was at the minimum value in January and February,and the maximum value in July.The SINDVI showed an increasing trend in most areas of the reservoir catchment,and the increased area accounted for 93.23%of the area of the TGRC.The increased areas were mainly distributed in the northeast of the TGRC,while vegetation degradation was obvious in the urban distribution areas.The LST showed a decreasing trend from 2000 to 2015,with an average decrease of 0.224?.The interannual variation trend of the LST in the TGRC was consistent with the drought events in Southwest China in 2006,and 2009 to 2013.The LST of spring,summer,autumn,and winter showed a downward trend,but the trend and decline degree were different.After the water level in the TGRC reached 175 meters in2010,the averaged LST from 2010 to 2015 was lower than that from 2000 to 2010through the analysis of interannual and seasonal scales,indicating that the water level rise had a certain cooling effect in the TGRC.The LST shows a downward trend in the most areas of the reservoir catchment,which accounts for 88.76%of the total area of the TGRC,and it is mainly distributed in the northeast part of the TGRC.The increased area of LST is located in the urban areas of the reservoir catchment,mainly in Yichang City,the main urban area of Chongqing City and the surrounding counties.The albedo showed a decreasing trend from 2000 to 2015,with an average decrease of 0.002.The albedo showed a downward trend in most areas of the TGRC,accounting for 52.4%of the total area of the reservoir catchment,and it is mainly distributed in the eastern districts and counties of the reservoir catchment.The increase of albedo was mainly in the urban areas at the Kushou and Kuwei.The albedo change at the seasonal scale shows a trend of“declining in spring and winter,increasing in summer and autumn”.During the period of 2000 to 2015,the land use type with the highest LST in the TGRC was artificial surface,followed by cultivated land and waterbody.The land use type with the highest SINDVI is forest,followed by cultivated land,waterbody,and artificial surface.The land use type with highest albedo is the artificial surface,followed by cultivated land,forest,and waterbody.During the study period,the LST of the artificial surface showed an increasing trend,increased by 1.37?.The LST of the forest showed a decreasing trend,decreased by 0.16?.The LST of waterbody showed an increasing trend,increased by 0.15?.The LST of cultivated land fluctuates greatly so its trend is not obvious.The SINDVI of all land use types showed an increasing trend during the study period.The albedo showed a declining trend during the study period,except for the artificial surface.Above changes are related to the continuous increase of artificial surface,forest and waterbody,and the decrease of cultivated land in the TGRC from 2000 to 2015,as well as influenced by the accuracy of MODIS products in some regions and physical and chemical properties of each land use type.From 2000 to 2015,the SINDVI was negatively correlated with the LST in the TGRC,and the SINDVI and albedo are mainly negatively correlated.The negatively correlated areas are mainly distributed in the eastern part of Kufu.The changes of land surface parameters with significant change region of land use in the TGRC were analyzed.The results showed that in the main urban areas of Chongqing City,the LST showed an increasing trend,due to the rapid urbanization.The SINDVI showd an increasing trend because of vegetation increasing in urban areas.The albedo shows a downward trend,which is caused by the increase of vegetation,and also influenced by product accuracy in the region.It also shows that the increase of vegetation may not effectively reduce the LST in urban areas where human activities are intense.Fengjie County,which located in the northeast TGRC,the forest area increased significantly.As a result,the SINDVI increased by 3.39 in 16 years.The LST and albedo showed declining trends,decreasing by 0.42?and 0.008,respectively.The increase in vegetation was the main reason for the decrease in LST and albedo.