关键词: 短期复合干旱高温事件, NDVI, 影响, 事件强度, 植被前期状态

Abstract: Aims China is a hotpot for compound drought and hot events, which pose significant threats to ecosystem stability. Although the impact of climate extremes on vegetation is modulated by pre-existing growth conditions, few studies have explicitly accounted for the vegetation preconditioning when assessing impacts. This study aims to disentangle the short-term impacts of compound drought-hot events from those of individual extremes on summer vegetation in China, specifically by isolating events that occurred under favorable pre-event growth conditions. Methods Using summer 8-day NDVI and meteorological data from 2001 to 2023, we analyzed the short-term impact of compound drought–hot events on vegetation in comparison with individual drought or hot events. Crucially, we isolated the specific impact of these events themselves, we restricted our analysis to samples exhibiting favorable vegetation status and no preceding extremes prior to the event onset. Important findings (1) All three event types triggered significant vegetation decline, with over 80% of areas exhibiting negative NDVI standardized anomalies. Although the national average impact of compound events (-0.27) approximated that of individual droughts (-0.26), significant spatial heterogeneity was observed. (2) In approximately 30% of regions (mainly arid/semi-arid areas like North and Northwest China), compound events caused greater damage than any individual event (synergistic effect). Conversely, in ~25% of areas (e.g., parts of northern Inner Mongolia), the impact of compound events was weaker than that of individual extremes (antagonistic effect). (3) The impact of compound events was strongly dependent on event intensity. Across all precipitation deficits, compound events consistently caused greater vegetation loss than individual droughts, with the disparity amplifying as drought severity increased. However, the relationship with temperature was nonlinear: under low-to-moderate heat stress, compound events were more damaging than individual hot events, whereas under high-intensity heat stress, compound events caused significantly less damage than individual heatwaves. These findings highlight the critical role of event intensity and vegetation preconditioning in determining ecosystem vulnerability to compound climate extremes.

Key words: Short-term Compound Drought and Heatwave, NDVI, Impact, Event Intensity, Vegetation Preconditioning