Study on the Characteristics of Flash Drought and the Response Regularity of Photosynthesis to Flash Drought in Different Vegetation Ecosystems in the Middle and Lower Reaches of the Yangtze River Basin.

In recent decades, flash drought events have frequently occurred in the humid regions of southern China. Due to the sudden onset and rapid intensification of these droughts, they often cause severe damage to vegetation photosynthesis. Our current understanding of the spatiotemporal evolution characteristics of flash droughts across different vegetation types remains limited. Moreover, insufficient consideration of the early stress of vegetation during flash droughts has constrained our understanding of the response regularity of vegetation photosynthesis to flash drought events. This study analyzes the spatial and temporal evolution characteristics of flash drought for different vegetation types in the middle and lower reaches of the Yangtze River Basin from 2000 to 2023. Using the flash drought event of 2013 as a case study, solar-induced chlorophyll fluorescence (SIF) and fluorescence yield (ΦF) were employed to further explore the Response Regularity of vegetation photosynthesis to flash drought. The results show that, over the past 24 years, the frequency of flash drought for different vegetation types in the middle and lower reaches of the Yangtze River Basin has decreased, but the total duration has increased, with forests experiencing a higher frequency of flash drought. Cropland photosynthesis is the most sensitive to flash drought, responding on the 10th day after the onset and reaching a negative anomaly by the 26th day. Forests and grasslands respond later, beginning on the 20th day and showing a negative anomaly by the 36th day. The findings of this study contribute to a deeper understanding of vegetation photosynthesis responses to flash drought and provide a reference for developing effective flash drought management strategies.