Response of vegetation to drought in the Tibetan Plateau: Elevation differentiation and the dominant factors

With a typical alpine grassland ecosystem, the Tibetan Plateau (TP) is a highly representative region to observe the effects of climate change on ecosystems. Continued global warming has increased the drought risk of TP, yet the response of vegetation to drought remains unclear. To understand the spatial heterogeneity of the vegetation response to drought and identify the key control factors of vegetation response to drought in different elevation intervals on TP, we introduced three vegetation indexes (EVI, LAI, and GPP) and multi-scale drought indexes, including the Standardized Precipitation Index (SPI) and Standardized Precipitation-Evapotranspiration Index (SPEI), to determine the spatial response of vegetation growth to drought from 2000 to 2015. Land surface temperature (LST), land cover, snow cover, population density, and soil texture were selected as potential control factors. The mean values of the maximum correlation coefficients for the six combinations indicated that 14.3%/12.0% (SPI/SPEI) of the vegetation growth on TP was significantly affected by water conditions (p < 0.05). The extent of vegetation growth responses to drought were mainly influenced by LST with the highest contribution rate of 65.8% at 3000-4500 m intervals. The response time is mainly dependent on the proportion of grassland, with the highest contribution rate of 81.7% at 4500-6000 m intervals. The results provide reasonable evidence for understanding the spatial heterogeneity of the elevation dependence of the alpine ecosystem response to drought.