Applicability of Flash Drought Definitions in China: Verification of Identification in Recent Three Years

Characterised by rapid development, flash droughts challenge timely responses and severely affect agricultural productivity, ecological stability, and socioeconomic resilience, making them a critical research focus. Existing studies reveal substantial spatiotemporal disparities in flash droughts identified by different definitions. Although definitional effectiveness varies regionally, systematic evaluation of their regional applicability remains limited. Flash drought definition involves two key components: drought indicator selection and the objective identification method. This study developed four definitions by combining two indicators – the soil moisture (SM) and evapotranspiration stress ratio (ESR) – with two methods: based on the change rate of percentiles (CROP) and based on percentiles of variation (POV). We evaluated definitional impacts on drought identification and validated results against documented flash droughts (2022–2024). The results show that drought indicators exert greater influence than identification methods. SM and ESR show distinct spatial patterns in identifying flash drought hotspots across China. POV criteria are stricter than CROP, requiring further threshold investigation. SM better identifies “high evapotranspiration demand, fast evapotranspiration rates, and relatively low initial SM” events, particularly in the humid region (south of Qinling-Huaihe Line), where flash droughts often manifest as “high-temperature-driven”, as evident in the Yangtze River Basin during summer 2022 and in central Sichuan in 2023. In contrast, ESR outperforms for detecting “high onset-stage evapotranspiration demand but limited evapotranspiration due to already very low initial SM” events, which are common in the transition region (north of the Qinling-Huaihe Line and south of Inner Mongolia), where flash droughts are typically “water-deficit-driven”, as observed in the Huanghuai region in summer 2024.