Effect of climate and ecological restoration on vegetation changes in the "Three-River Headwaters" region based on remote sensing technology

Surface temperature and precipitation are factors effecting vegetation growth. Vegetation coverage change is one of the important factors influencing global and regional climate change. Dynamic monitoring of vegetation change can reflect the trend of climate change to a certain extent. Three-River Headwaters are located in the hinterland of the Qinghai-Tibet Plateau. It has the characteristics of "high, cold, and dry" (higher altitude, cold and dry weather) and its ecosystem is fragile. In recent years, with the global climate change, a series of eco-environmental problems such as river flow cutoff, permafrost degradation, and vegetation destruction has occurred in the headwaters area, which are closely related to climate and vegetation changes. At the same time, in order to solve the problem of ecological environment degradation in the region, various ecological restoration policies have implemented. Several uncertainties in the relationship between vegetation and climate change in the Three-River Headwaters region. This study aims to find out the uncertainties. In this study, the spatial distribution of vegetation coverage was calculated by using NDVI (normalized difference vegetation index) from the first-level product of MODIS (moderate resolution imaging spectroradiometer) remote sensing data. Combining policy factors, the relationship between rainfall, surface temperature, and vegetation growth status were analyzed. The results show that during the study period (1948-2019), the temperature rose significantly and the rainfall increased especially after the implementation of ecological restoration policy (after 2000). Vegetation coverage increased year-by-year (2000-2015). The rainfall effect on surface temperature and vegetation growth, when the summer rainfall increased, the temperature decreased, leads to vegetation coverage decreased (for example, 2001, 2003, 2008 and 2011); the dependence of vegetation on rainfall has obvious lag in Three-River Headwaters in summer. In the years with suitable rainfall and higher temperature in summer, the vegetation grows better and the vegetation coverage increases. This is mainly because the Three-River Headwaters is located in the alpine zone, and vegetation growth is more dependent on temperature. The implementation of ecological restoration policy promotes vegetation coverage. Studying the impact of climate and policy factors on vegetation cover is of great scientific significance and practical value for understanding the ecological restoration mechanism in high cold and arid regions.