Evapotranspiration stress intensifies with enhanced sensitivity to soil moisture deficits in a rapidly greening China

Abstract

Amidst drastic environmental changes, the intricate interplay and feedback mechanisms in the water–vegetation–atmosphere nexus experience alteration. Previous research primarily centres on the responses among variables within this system, with little known about whether and how these responses (sensitivities) change. Here, we employ the Evapotranspiration Stress Index (ESI) to represent the equilibrium of the nexus and develop a memory dynamic linear model based on Bayesian forward filtering. The model takes into account the carry-over effect in the “dry gets drier” self-amplify loop, allowing for a more effective estimation of the ESI time-varying sensitivity to associated influencing factors. Our analysis reveals that from 1950 to 2020, mainland China experienced a notable 4.74 % escalation in evapotranspiration stress. Surface soil moisture serves as a primary driver, whose sensitivity to ESI has surged by 9.49 % in the last decade compared to the early 2000s. Vapour pressure deficit (VPD) and leaf area index (LAI) also exerted a substantial role, with their sensitivities fluctuating approximately 22.91 % and −45.77 %, respectively. Moreover, the greening pace is linked to an increase in soil moisture sensitivity and a decrease in VPD sensitivity, suggesting that rapid greening may alter the ecological resilience against soil deficit and atmospheric drought. In comparison, the widely used moving window multiple linear regression (MLR) significantly overestimates sensitivity fluctuations, necessitating prudent interpretation of numerical estimates in related research findings. Our findings underscore the spatiotemporal variations in sensitivity, enriching the comprehension of ecosystem reactions to external factors, and offer essential insights for advancing greening endeavours.