Abstract Submission: Several definitions of flash droughts have been proposed in literature. Despite the differences, most definitions concentrate both on their rapid intensification (i.e., the “flash” component ) and on the actual occurrence of moisture limitation leading to impacts (i.e., the “drought”). This framework distinguishes flash drought from slower-onset conventional drought, while also ensuring that these events lead to impacts such as reduced soil moisture or poor vegetation health. Numerous authors have used these guiding principles to devise quantitative flash drought definitions using various datasets. Here, a general analytical framework is developed, able to characterize from a probabilistic standpoint droughts with rapid onset causing significant impacts on soil moisture limitations. The framework capitalizes on the standardized nature of the usually adopted indices and therefore can be applied to any standardized drought index representative of soil moisture and/or evapotranspiration (e.g. EDDI, SPEI). More specifically, capitalizing on the intrinsic normality of the standardized indices, it is possible to compute analytically probabilities related to various types of drought events, considering both their inception, evolving speed and intial/final severity. The proposed methodology is flexible enough to accomodate for different definitions of flash droughts and can be fitted to take into account flash droghts that evolve into normal droughts. The methodology is applied to Sicily region, Italy, characterized by a semi arid climate and that is currently experiencing one of the most devastating droughts observed in the last decades. Results of the application reveal the feasibility of the proposed methodology to characterize from a probabilistic standpoint observed droughts.
