Long-term monitoring of the ecological environment changes is helpful for the protection of the ecological environment.Based on the ecological environment of the Sahel region in Africa,we established a remote sensing ...Long-term monitoring of the ecological environment changes is helpful for the protection of the ecological environment.Based on the ecological environment of the Sahel region in Africa,we established a remote sensing ecological index(RSEI)model for this region by combining dryness,moisture,greenness,and desertification indicators.Using the Moderate-resolution Imaging Spectroradiometer(MODIS)data in Google Earth Engine(GEE)platform,this study analyzed the ecological environment quality of the Sahel region during the period of 2001-2020.We used liner regression and fluctuation analysis methods to study the trend and fluctuation of RSEI,and utilized the stepwise regression approach to analyze the contribution of each indicator to the RSEI.Further,the correlation analysis was used to analyze the correlation between RSEI and precipitation,and Hurst index was applied to evaluate the change trend of RSEI in the future.The results show that RSEI of the Sahel region exhibited spatial heterogeneity.Specifically,it exhibited a decrease in gradient from south to north of the Sahel region.Moreover,RSEI in parts of the Sahel region presented non-zonal features.Different land-cover types demonstrated different RSEI values and changing trends.We found that RSEI and precipitation were positively correlated,suggesting that precipitation is the controlling factor of RSEI.The areas where RSEI values presented an increasing trend were slightly less than the areas where RSEI values presented a decreasing trend.In the Sahel region,the areas with the ecological environment characterized by continuous deterioration and continuous improvement accounted for 44.02%and 28.29%of the total study area,respectively,and the areas in which the ecological environment was changing from improvement to deterioration and from deterioration to improvement accounted for 12.42%and 15.26%of the whole area,respectively.In the face of the current ecological environment and future change trends of RSEI in the Sahel region,the research results provide a reference for the construction of the"Green Great Wall"(GGW)ecological environment project in Africa.展开更多
Vegetation is a significant factor in the energy and water cycles.Changes in vegetation are affected by the natural environment and human activities.In this study,the Dalong Reservoir on the Ningyuan River in Sanya,Ha...Vegetation is a significant factor in the energy and water cycles.Changes in vegetation are affected by the natural environment and human activities.In this study,the Dalong Reservoir on the Ningyuan River in Sanya,Hainan,China,was taken as an example to set one type of buffer zone with the reservoir dam site as the center,and two types of horizontal and vertical buffer zones outwards from both banks of the river,and Landsat 5 remote sensing image data and the vegetation data were applied.A coverage estimation model was used to study the temporal and spatial changes in surface vegetation in three types of buffer zones,and the characteristics of the surface vegetation changes in the preterm,midterm and late-term reservoir construction periods were analyzed.The results showed that,(1)During the years 2000 and 2010,the vegetation coverage first decreased and then increased with time in the scope of the research.During preterm construction(2000-2004),the vegetation coverage in the upstream region decreased while that in the downstream region increased.During midterm construction(2004-2006),the declining rate of vegetation coverage downstream was greater than that upstream,but the influence of reservoir construction on vegetation coverage decreased over time in the late-term construction period(2007-2010);(2)Along the direction of the river length,the vegetation coverage showed a downtrend along with the river flow direction during the whole period(2000-2010),and the influence of reservoir construction on vegetation coverage gradually decreased as the distance from the reservoir increased;(3)Along the direction of the river width,the vegetation coverage in the preterm and midterm construction periods(2000-2006)increased with increasing distance from the riverbanks;(4)The vegetation coverage showed a significant increasing trend with increasing distance from the reservoir.The research results can provide a theoretical reference for reducing the risk of vegetation degradation,strengthening the governance of the ecological environment,and promoting the ecological construction of“landscapes,forests,fields,lakes and grass”.展开更多
基金This research was financially supported by the West Light Foundation of the Chinese Academy of Science(2017-XBQNXZ-B-018)the National Natural Science Foundation of China(41861144020)the National Key Research and Development Program of China-Joint Research on Technology to Combat Desertification for African Countries of the“Great Green Wall”(2018YFE0106000).
文摘Long-term monitoring of the ecological environment changes is helpful for the protection of the ecological environment.Based on the ecological environment of the Sahel region in Africa,we established a remote sensing ecological index(RSEI)model for this region by combining dryness,moisture,greenness,and desertification indicators.Using the Moderate-resolution Imaging Spectroradiometer(MODIS)data in Google Earth Engine(GEE)platform,this study analyzed the ecological environment quality of the Sahel region during the period of 2001-2020.We used liner regression and fluctuation analysis methods to study the trend and fluctuation of RSEI,and utilized the stepwise regression approach to analyze the contribution of each indicator to the RSEI.Further,the correlation analysis was used to analyze the correlation between RSEI and precipitation,and Hurst index was applied to evaluate the change trend of RSEI in the future.The results show that RSEI of the Sahel region exhibited spatial heterogeneity.Specifically,it exhibited a decrease in gradient from south to north of the Sahel region.Moreover,RSEI in parts of the Sahel region presented non-zonal features.Different land-cover types demonstrated different RSEI values and changing trends.We found that RSEI and precipitation were positively correlated,suggesting that precipitation is the controlling factor of RSEI.The areas where RSEI values presented an increasing trend were slightly less than the areas where RSEI values presented a decreasing trend.In the Sahel region,the areas with the ecological environment characterized by continuous deterioration and continuous improvement accounted for 44.02%and 28.29%of the total study area,respectively,and the areas in which the ecological environment was changing from improvement to deterioration and from deterioration to improvement accounted for 12.42%and 15.26%of the whole area,respectively.In the face of the current ecological environment and future change trends of RSEI in the Sahel region,the research results provide a reference for the construction of the"Green Great Wall"(GGW)ecological environment project in Africa.
基金This research was supported by the National Natural Science Foundation of China(Grant No.41877276)the Chinese Natural Science Foundation of Shanxi Province(Grant No.201901D111052).
文摘Vegetation is a significant factor in the energy and water cycles.Changes in vegetation are affected by the natural environment and human activities.In this study,the Dalong Reservoir on the Ningyuan River in Sanya,Hainan,China,was taken as an example to set one type of buffer zone with the reservoir dam site as the center,and two types of horizontal and vertical buffer zones outwards from both banks of the river,and Landsat 5 remote sensing image data and the vegetation data were applied.A coverage estimation model was used to study the temporal and spatial changes in surface vegetation in three types of buffer zones,and the characteristics of the surface vegetation changes in the preterm,midterm and late-term reservoir construction periods were analyzed.The results showed that,(1)During the years 2000 and 2010,the vegetation coverage first decreased and then increased with time in the scope of the research.During preterm construction(2000-2004),the vegetation coverage in the upstream region decreased while that in the downstream region increased.During midterm construction(2004-2006),the declining rate of vegetation coverage downstream was greater than that upstream,but the influence of reservoir construction on vegetation coverage decreased over time in the late-term construction period(2007-2010);(2)Along the direction of the river length,the vegetation coverage showed a downtrend along with the river flow direction during the whole period(2000-2010),and the influence of reservoir construction on vegetation coverage gradually decreased as the distance from the reservoir increased;(3)Along the direction of the river width,the vegetation coverage in the preterm and midterm construction periods(2000-2006)increased with increasing distance from the riverbanks;(4)The vegetation coverage showed a significant increasing trend with increasing distance from the reservoir.The research results can provide a theoretical reference for reducing the risk of vegetation degradation,strengthening the governance of the ecological environment,and promoting the ecological construction of“landscapes,forests,fields,lakes and grass”.
