Quantitatively assessing the impacts of climate change and human activities on vegetation dynamics in the Lancang River Basin

Abstract

[Objective] The impact of vegetation on aspects such as water-sediment balance, exchange of biogenic elements, and ecosystem stability is considered important. The Lancang River is regarded as an important water conservancy project and water resources regulation center in southwest China, with its vegetation dynamics being deemed crucial for flood safety, water supply security, and ecological security in the basin.[Methods] The study area was focused on the Lancang River Basin. Utilizing time series meteorological data from 1998 to 2020, as well as Normalized Difference Vegetation Index(NDVI) data, the spatial-temporal variations of vegetation dynamics in the Lancang River Basin were analyzed. The analysis included the utilization of the Mann-Kendall trend test and Sen's Slope estimation, and the impacts of climate change and human activities on vegetation dynamics in the Lancang River Basin were quantitatively assessed using the Partial Least Squares Structural Equation Model.[Results] During the period from 1998 to 2020, it was observed that the annual growth rate of NDVI during the growing season in the Lancang River Basin was 0.004 2/year, indicating a significant increasing trend. The growth rates in the Qinghai and Tibet sections were 0.002 0/year and in the Yunnan section was 0.005 3/year. It was noted that the proportion of regions with significantly improved vegetation in the basin exceeded 40%, while regions with severe degradation were less than 5%. Furthermore, it was found that the NDVI in spring, summer, and autumn all exhibited significant growth, with the fastest growth being observed in spring and the slowest in summer. The fastest growth season in the Qinghai and Tibet sections was summer, with the slowest growth occurring in spring. In the Yunnan section, the fastest growth seasons were spring and autumn, with relatively slower growth in summer. The average impact of terrain factors on vegetation was-0.085, human activities were found to have an average impact of 0.009, and climate factors were noted to have an average impact of 0.451.[Conclusion] Currently, temperature is considered to be the main climate factor affecting vegetation growth in the study area, with human activities being identified as having a relatively weak impact on vegetation dynamics. It was also observed that terrain factors indirectly affect vegetation growth by regulating climate factors.

Keywords

precipitation / temperature / human activities / NDVI / Lancang River Basin / PLS-SEM / spatiotemporal variation