Drought Timing Differentiates the Drought Responses of Vegetation Growth on the Tibetan Plateau

The Tibetan Plateau, with its great hydrothermal gradients and diverse ecosystems, is considered vulnerable to climate change. Extreme drought can have detrimental effects on carbon sequestration in terrestrial ecosystems by disrupting plant eco-hydrological processes. Such effects are presumed to vary and depend on the vegetation types, environmental factors and drought properties. The drought timing has been widely highlighted in drought studies at both regional and site scales. However, the systematic insight into the impact of drought timing on the ecosystem functioning over the Tibetan Plateau remains unclear. In this study, we investigated the responses of vegetation greenness to meteorological drought and attributed them to the drought properties, climatic and edaphic factors. We found that the timing of drought plays a predominant role in regulating vegetation drought responses on the Tibetan Plateau. Notably, we observed significant differences in vegetation responses between late growing season drought and non-late growing season drought. In addition to drought timing, soil moisture and long-term hydrothermal conditions also played a significant role. Furthermore, our study revealed that alpine grassland was more sensitive to the drought timing, soil moisture and sand content than woody plants. We discovered a significant interplay between rainfall at hottest quarter and drought timing, with the role of drought timing weakening as the rainfall at hottest quarter increases. These findings underscore the crucial role of drought timing in shaping ecosystem functioning in response to the changing climate regime over the Tibetan Plateau and provide crucial insights into the improvement of land surface models. Global warming is leading to increased drought stress worldwide. The intensification of extreme droughts has adverse effects on vegetation growth in large vegetated regions. The timing of drought events is especially important when vegetation growth exhibits high seasonality. However, the responses of vegetation growth to the timing of extreme droughts and the underlying drivers are poorly understood on the Tibetan Plateau, despite being a hotspot region experiencing marked warming. Here, we quantified the impacts of drought on the vegetation growth across diverse ecosystems on the Tibetan Plateau based on remote-sensing observations. Our results pointed out that drought timing is the dominant factor regulating the responses of vegetation to meteorological drought. Specifically, we found that alpine grassland exhibits greater sensitivity to the timing of drought events compared to forest and bushwood. Moreover, our study revealed that vegetation in regions with higher summer rainfall is less sensitive to drought timing. These findings underscore the vital role of drought timing in regulating ecosystem functioning across the Tibetan Plateau under future climate change. The occurrence of extreme drought events decreases significantly and temporally in the westerlies and transition domains Drought timing plays a dominant role in determining the vegetation responses to extreme drought The sensitivity of vegetation growth to drought timing strongly depends on rainfall at the hottest quarter