Temporal and Phenological Modulation of the Impact of Increasing Drought Conditions on Vegetation Growth in a Humid Big River Basin: Insights From Global Comparisons

Abstract

As the upward trend in extreme drought continues with climate change, terrestrial vegetation growth is assumed to become largely reduced. We investigated anomalies of remote sensing vegetation indexes under droughts across the upper Yangtze River (UYR) basin, characterized as humid but having experienced frequent seasonal droughts from 2000. Then we compared global big river basins by focusing on the Nile and Congo basins, which have similar characteristics to the UYR. The vegetation across the UYR was affected by water stress in recent years but shows reduced sensitivity to drought. The compound effect of drought timing and phenology largely drives the response. Results show that late-season droughts generally have a greater impact on vegetation growth compared to early season droughts, with alpine grasslands showing particularly pronounced responses due to their ecological features such as shallow root depth and aggressive hydrological behavior. The Nile basin, similar to the UYR basin, exhibits pronounced late-season vegetation vulnerability, highlighting shared patterns of drought impact across heterogeneous landscapes. In contrast, the tropical rainforests in the Congo basin demonstrate greater resilience, supported by complex root systems, dense canopies, and low cloud cover that reduces evaporation. This study underscores the importance of considering regional ecological characteristics, drought timing, and phenological stages in assessing vegetation responses to drought. These insights are critical for predicting and managing ecosystem resilience under changing climatic conditions.