气候与人类活动对丹江口水源区植被覆盖变化的影响.

Vegetation coverage in catchment has a direct impact on its ecological environment, and monitoring vegetation coverage change and its determinants is important to reconstruct effectively ecological engineering projects to sustain economic development without compromising ecological environment. Danjiangkou Reservoir is a waterhead at the middle route of the South-North Water Transfer Project in China, and its ecological environment has a direct impact on quality and quantity of the water in the transferring cannel. Available study on vegetation coverage change in this area is problematic, including short experiment duration and inadequate evaluation of the impact of the human activities. We address this knowledge gap in this paper using data extracted from GIMMS NDVI and MODIS NDVI. The empirical orthogonal teleconnection (EOT) algorithm was used to reconstruct the normalized difference vegetation index (NDVI) from 1982 to 2018, from which we analyzed the spatiotemporal change in the vegetation coverage and individual contribution of climate factors and human activities to the vegetation coverage changes. The results revealed that NDVI showed an oscillating increase from 1982 to 2018 at an average rate of 0.002 9 /a (P<0.05). Spatially, 89.93% of the studied areas saw a first-year increase in NDVI, and 10.06% witnessed a first-year decrease. Temperature impacted on NDVI most with a correlation coefficient of 0.792 (P<0.05), followed by precipitation with a correlation coefficient of - 0.43 (P<0.05). The influence of climate factors on vegetation coverage varied spatially. In mountainous areas, vegetation growth was affected by precipitation and temperature combined, while in basins and river valleys characterized by low and flat terrain, NDVI was positively correlated with temperature and negatively with precipitation, both at significant level. Human activities impacted on vegetation coverage in two opposite ways. On the one hand, human activity in 67.74% of the studied areas had a positive effect on vegetation coverage due to engineering measures being taken to restore and improve ecological functions of these area. On the other hand, human activity in 32.26% of the studies areas had a detrimental impact on vegetation coverage due to unsustainable activities used in social-economic development. The impacts of climate and human activities on regional vegetation coverage were separated by the residual method, and the results indicated that overall contribution of the climate factors to the vegetation coverage change was 92.14%, compared to the 7.86% from the human activities. Spatially, in areas with more human activities, such as areas that had taken ecological measures or in the proximity of central city, human activities have been becoming the determinants of the NDVI change. [ABSTRACT FROM AUTHOR]