Biophysical impacts of vegetation dynamics largely contribute to climate mitigation in High Mountain Asia

Abstract

Satellite-driven and site observational data show that global warming has greatly enhanced vegetation activity (greening), with a broad upward trend in vegetation indices (VIs). However, the biophysical impact of vegetation on land surface temperature (Ts) is widely unknown, particularly in High Mountain Asia (HMA). In this study, we assessed vegetation dynamics in HMA from 2000 to 2020 and used intrinsic biophysical mechanism (IBM) models to quantify the biophysical feedback effects of vegetation on Ts. The results illustrate that, during the study period, HMA has undergone greening at a rate of 0.505 × 10−3 W m−2 μm−1 sr−1 yr−1 (solar-induced chlorophyll fluorescence: SIF) and 1.7 × 10−3 yr−1 (normalized vegetation index: NDVI), accounting for 52.75% and 47.24% of the total number of pixels, respectively. However, vegetation browning has occurred in areas such as the central Tien Shan and southeastern Tibet. Meanwhile, 64.22% (SIF) and 53.68% (NDVI) of the vegetation area in HMA showed a negative sensitivity of Ts to vegetation activity, particularly herbaceous and scrub vegetation in Inner Tibet and eastern Kun Lun. Additionally, the Bovine ratio and aerodynamic drag (ra) exhibited a negative sensitivity to vegetation activity. Most importantly, the vegetation activity-induced temperature changes were -0.278 K (ΔTNDVICIBM), -0.538 K (ΔTSIFCIBM), 0.028 K (ΔTNDVISIBM), and 0.024 K (ΔTSIFSIBM). Moreover, in the sensitivity method (ΔTVegSIBM), vegetation cooling was detected in more than half of the pixels in HMA and was even more pronounced with SIF, accounting for 64.22% compared to 53.68% with NDVI. Enhanced vegetation activity alters the original balance of latent and sensible heat fluxes (Le,H) and increases the turbulent heat transfer between land and atmosphere, particularly Le. Our findings have important implications for understanding the response and feedback of vegetation dynamics to climate change in arid alpine regions.