A spatiotemporal deconstruction-based approach for identifying flash drought expansion: Normalized Area-Time Accumulation curve

Though flash drought is an intrinsically three-dimensional phenomenon that evolves in both temporal and spatial dimensions, most studies have overlooked its spatiotemporal features by analyzing its characteristics at individual grid points. The rapid expansion of drought over time and space also brings great challenges for drought monitoring and management strategies. Focusing on the mapping of rapid development trajectories of drought in the three-dimensional space, this study proposes the Normalized Area-Time Accumulation (NATA) curve to describe the evolution characteristics of flash drought. Using the NATA curve, information about the expansion rate of drought area over time and the dominant severity of drought area can be extracted. On this basis, such drought events were classified and investigated, considering drought monitoring difficulty and potential drought damages. Results showed that the shape of proposed NATA curve and the slope of curves of varying severity levels had explicit indicative function for distinguishing drought events characterized by “flash” and “drought” events from traditional slowly-evolving drought events. Drought events which have a rapid rate of area expansion and high drought severity mostly meets the characteristics of flash droughts in the spatiotemporal dimensions. The findings highlight the significance of incorporating information on drought area expansion with time for an efficient recognition and improved accuracy of rapid drought development from a three-dimensional perspective. This is a step forward for flash drought identification in a higher dimension. The proposed NATA curve provides intuitive and comprehensive information on how drought evolves over time and space and is a promising alternative method to analyze drought characteristics from a three-dimensional perspective.