Assessing the response of vegetation photosynthesis to flash drought events based on a new identification framework

Flash drought events pose serious threats to terrestrial ecosystems due to their rapid intensification. However, the comprehensive assessment of recovery stage in flash drought is hindered by the insufficient consideration of reduplicative decline in soil moisture. Besides, how the vegetation photosynthesis respond to flash drought remains unknown. Here, a new method for explicitly characterizing flash drought events was proposed, incorporating both development rate and duration, with particular emphasis on the process of soil moisture change during the recovery stage. Then the temporal and spatial evolutions of the flash drought over the Pearl River Basin were analyzed. Solar-induced chlorophyll fluorescence (SIF) was used to explore the responses of different vegetation types to flash drought. The results indicated that the onset speed may be increasing, and the flash drought in 2007 was quite serious. Most flash drought events lasted 32 to 48 days. Besides, this study focused on the response of forests, grasslands and crops to flash drought, and the forestlands were less sensitive to flash droughts, while croplands experienced the most flash drought events, and the time of photosynthesis loss of croplands was the shortest. Moreover, precipitation deficit, high temperature, high evapotranspiration (ET) and high potential evapotranspiration (PET) were the main driving factors triggering flash drought. The soil moisture was above 40th percentile after the end of a flash drought, which demonstrate the accuracy of the framework in identifying the development of flash drought in the concern area. Our findings also demonstrated the great effectiveness of SIF in monitoring the resistance of ecosystems, deepening our understanding of the response of vegetation photosynthetic capacity to flash drought events.