Vegetation change responses to climate change and human activities in southwest alpine canyon areas of China from 2000 to 2019

The southwest alpine canyon area is one of the most typical ecologically fragile areas in the world. It is a high demand to explore the spatiotemporal variations of vegetation and its response to climate change and human activities in this region. The relative contributions of climate change and human activities can also be quantified for ecological restoration. Among them, the normalized difference vegetation index (NDVI) can be expected to serve as the potential indicator for the vegetation dynamic growth conditions, due to the high sensitivity to the vegetation. In this study, the NDVI dataset was collected to examine the spatiotemporal variations from 2000 to 2019. The future trends of NDVI were then predicted using the Theil-Sen trend analysis, Mann-Kendall significance test, and Hurst index in conjunction with the meteorological factor datasets. A correlation and residual analysis were finally conducted to explore the response of NDVI to climate change and human activities. The results showed as follows: 1) The overall NDVI from 2000 to 2019 showed a fluctuating upward trend on the temporal scale, with a growth rate of 0.0046/a. The proportion of areas with an upward trend in the NDVI was 85.59% on the spatial scale, indicating significant vegetation recovery. However, some localized areas with a downward trend of NDVI accounted for 14.41% of the study area. The changing trend of NDVI continued to be predominantly upward in the future, where 82.34% of the study area was an upward trend, while 17.66% was a downward trend. A significant decrease in NDVI was found in the junction area between Changdu and Linzhi City in the Tibet Autonomous Region. There was also a risk of a further decrease in the NDVI in this area in the future. 2) The temperature and solar radiation increased at the rates of 0.02 ℃/a and 6.92 MJ/(m²·a), respectively, against the backdrop of regional climate warming and drying. But the precipitation decreased at a rate of −2.97 mm/a. The NDVI showed different responses to the various climatic factors, with a positive correlation with the temperature and solar radiation overall, but a negative correlation with the precipitation. Among them, the temperature posed a much stronger influence on the NDVI change than solar radiation and precipitation, indicating the dominant climatic factor on NDVI change. 3) Both climate change and human activities shared positive and negative effects on vegetation change. Specifically, a positive trend was found in most cases. Vegetation change in 85.10% of the study area was influenced by both climate change and human activities. Human activities were taken as the first driving factor, and climate change was the secondary driving factor, with relative contribution rates of 68.67%, and 31.33%, respectively. The finding can provide a scientific basis for the ecological and environmental construction in regional green and sustainable development.