Interannual trends of vegetation and responses to climate change and human activities in the Great Mekong Subregion

Abstract

Vegetation growth in the Great Mekong Subregion (GMS) is important to the global carbon cycle. However, the interannual patterns in vegetation growth and their causes are not fully understood. Here, the spatiotemporal pattern of vegetation interannual fluctuations in the GMS was investigated using the CEEMDAN and BFAST algorithms, and the relationships between climatic and anthropogenic factors were further explored using partial correlations and multiple linear regression. The results are as follows: (1) The interannual variation of the NDVI at the GMS regional scale shows a slight upward trend, with an average growth rate of 5 × 10 -5 /year and two segments: a significant greening before 1985 and a slowing down of the greening trend from 1985 to 2013. (2) For the spatiotemporal variation, about 47 % of the GMS showed a greening-to-greening trend, and the cropland's NDVI slightly declined after the breakpoint. In addition, about 12.67 % of the GMS experienced continuous browning before and after the breakpoint. (3) The effects of temperature, precipitation, and radiation on vegetation growth showed spatiotemporal heterogeneity. Temperature frequently impacted eastern and coastal areas (i.e., Yunnan, Vietnam, and the southern part of Myanmar) before the breakpoint, whereas total solar radiation, as the main climate-related driver, mainly influenced high-elevation areas of the GMS after the breakpoint. (4) The impacts of human activities (e.g., human population and GDP per capita growth rate) on NDVI interannual variations were mostly negative and were most severe in areas with dense forests. Based on our results, enhanced agricultural activities and improved agricultural management levels would benefit NDVI growth. • The Great Mekong Subregion showed a small increasing trend in NDVI interannual variation. • Changes in interannual vegetation fluctuation mainly occurred in the 1980s and 2000s. • 39.93 % of vegetation had a browning trend hidden in the overall greening trend. • Before and after the breakpoint, interannual variations in NDVI were mostly caused by changes in temperature and radiation. • Economic expansion slowed NDVI interannual growth, notably in dense forests.