U.S. Flash Droughts—Definitions and Dynamics

The term “flash drought” typically refers to rapidly developing agricultural or ecological droughts that occur at a timescale of several weeks or less. Multiple studies have introduced different definitions for flash droughts which are valuable in advancing descriptive understanding, but there is still no standard quantitative definition for flash droughts that can be applied consistently within predictive models and that captures the critical fact that the droughts intensify rapidly. We are testing a set of definitions by considering vegetation's central role in flash drought evolution and the transition of the land surface into water stressed conditions as critical factors in drought development. Each definition is tested for stability and ability to capture the temporal and spatial characteristics of highly studied flash drought events and evaluate the consistency between observed droughts. The proposed definitions are based on two criteria: (1) quantifying rate of intensification relative to local climatology, (2) defining a local threshold to set the end of the rapid intensification period. An inventory of flash drought events is generated for historical data and classified to understand the main drivers of flash droughts over CONUS. Results will aid in the development of more skillful statistical and dynamical forecast systems to inform drought preparation and mitigate economic losses.