Ecological and vegetation responses in a humid region in southern China during a historic drought.

Climate change has triggered more frequent drought occurrence, which can have devastating impacts on the ecosystem functions. Studies on vegetation behavior during droughts have mainly focused on arid/semi-arid regions, yet the ecological and vegetation responses during drought in humid regions remain unclear. Here we systematically evaluated the evolution of the historic drought occurred in the humid Pearl River Basin in 2021 and quantified the vegetation responses using a multitude of vegetation indicators. Analyses showed that the East River Basin and North River Basin were the most severely hit by drought, which enhanced surface temperature and evapotranspiration, and caused soil moisture and terrestrial water storage deficits. Mean vegetation response time was shorter based on solar-induced fluorescence (SIF, 2.7 months) and the water use efficiency (WUE, 2.8 months), followed by the gross primary productivity (GPP, 3.2 months), and longer using the normalized difference vegetation index (NDVI, 4.2 months) and the vegetation optical depth (VOD, 5.0 months). By contrast, over 90% of the ecosystems recovered to their normal states within 3 months using all indicators. The results implied that the NDVI lacks sensitivity to changes in water stress in humid regions, and revealed that vegetation in humid regions may respond slowly and recover rapidly under droughts, which may relate to the water availability that enhances the resistance and resilience of the ecosystems.