Research On Dynamic Monitoring Of Vegetation Coverage In Hotan Area Based On MODIS NDVI

Fractional vegetation coverage(FVC)is an important parameter reflecting plant growth and provides an important reference for the study of land surface environmental changes.In the context of global warming,vegetation coverage,as a key indicator of climate change,has been widely used in the research fields of ecosystem assessment,land degradation and air pollution monitoring.The change of vegetation coverage is the result of the interaction of natural factors and human factors.Remote sensing monitoring of dynamic change of vegetation coverage has become an important global research topic.It is of great significance to solve regional ecological environment problems,maintain the stability of ecosystem and the sustainable development of social economy in desert oasis area.Based on remote sensing and geographic space information technology,this study USES the 2000-2018 the MODIS NDVI product data and combined with a variety of data sources,through the estimation of inversion of vegetation coverage,nearly 19 years in hotan region,the vegetation coverage change of quantitative analysis,explore the natural factors and human factors affecting vegetation coverage,The main research conclusions include the following aspects:(1)The seasonal and interannual variations of NDVI in Hotan region from 2000 to 2018showed that the NDVI in the artificial plain oasis and the pluvial plain of the Kunlun Mountains was at a high level and showed a steady increasing trend,while the NDVI in the Taklimakan Desert and the Kunlun Mountains was at a very low level and showed a slight decreasing trend.NDVI was significantly higher in summer than in spring and autumn.The spatial distribution of NDVI showed obvious spatial heterogeneity,and the spatial difference of NDVI between the plain oasis area and the mountain area was particularly obvious.In recent 19 years,the variation trend of NDVI was between-0.02 and 0.04,and the area with an increasing trend accounted for 2.29%of the total area.The NDVI of Kunlun Mountain and Taklimakan Desert showed a slight decreasing trend,accounting for 86.26%of the total area of the study area.The areas that were basically unchanged accounted for 11.56%.In general,NDVI showed an obvious increasing trend in the artificial plain oasis and the piedmont diluvial plain of Kunlun Mountains,while it showed a weak decreasing trend in the mountainous area of Kunlun Mountains and the Taklimakan Desert.(2)In recent 19 years,about 19.68×10~4km~2of vegetation coverage in Hetian area has not changed significantly,accounting for 79.42%of the total area of the study area.The area with slight degradation and slight improvement of vegetation cover was 2.24×10~4km~2and 2.35×10~4km~2,accounting for 9.04%and 9.47%of the total area of the study area,respectively.Areas with significant degradation and improvement accounted for a lower proportion.Analysis of2000-2018 years,hotan region of vegetation coverage mild degradation and slightly improved obviously,and mild improvement area mainly in artificial oasis plain area and the diluvial plain of the kunlun mountains,mild degradation occurs mainly in the taklimakan desert and kunlun mountains area of zhongshan,significant degradation area mainly in high altitude of kunlun mountains area,The areas where vegetation coverage improved significantly were concentrated in plain oases with human activities.On the whole,the oasis ecosystem is relatively stable,while the desert ecosystem is relatively fragile.(3)From 2000 to 2018,the vegetation coverage in the study area showed an overall increasing trend,and the increased area accounted for 12.88%of the total area,mainly concentrated in the plain oasis area and the intersection area of mountain and plain.Under the influence of climate change,the vegetation coverage in the Taklimakan Desert in the north and Kunlun Mountain in the south of Hotan region showed an obvious decreasing trend due to the little disturbance from human activities,and the change area accounted for 0.38%of the total area of the study area.The analysis shows that human activities and climate factors have obvious effects on vegetation coverage in Hotan area,which is mainly affected by human activities in the plain oasis area,and mainly affected by climate conditions in the mountainous area.(4)Since 2000 to 2018,affected by air temperature,precipitation and topographic factors,the overall level of vegetation coverage in Hetian area was low.The high vegetation coverage areas were mainly located in the plain oasis area with better hydrothermal conditions and the Kunlun mountain diluvial plain.The medium and low vegetation coverage were mainly distributed in the desert-oasis transition zone.Vegetation free areas are mainly concentrated in the Taklimakan Desert with little precipitation and high evaporation and the Kunlun Mountain alpine zone with extremely low temperature.At low altitudes,there was a significant positive correlation between altitudes and vegetation cover,while at high altitudes,there was an opposite trend.The vegetation coverage of the north and northeast slopes was higher than that of the south and southwest slopes.Human factors,such as land use pattern and population and economy,have significant effects on vegetation coverage in oasis areas,while in non-human areas,the dynamic change of vegetation coverage is mainly affected by climate factors.