Flash Drought Characteristics Based on the U.S. Drought Monitor

Drought can develop and intensify in a short amount of time and result in major agricultural losses if they are not predicted and detected in a timely manner. Understanding the characteristics of flash drought events, when and where these events occur, their causes, and the prediction of the onset of such events on subseasonal timescales is of critical importance for impact assessment, disaster mitigation, and loss prevention. In this study, we employ a rate-of-change approach and define a flash drought event as a drought event with greater than or equal to two categories degradation in a 4-week period based on the U.S. Drought Monitor. Unlike conventional drought that can occur year-round and everywhere in the United States, flash drought has preferred seasons and locations to occur, mostly in the warm season and over the central United States. Widespread flash drought over the United States is largely correlated to La Niña episodes. In contrast to conventional drought, which is mainly driven by precipitation deficits, anomalously high evapotranspiration rates, caused by anomalously high temperatures, winds, and/or incoming radiation, are usually present before the onset of flash drought. As a result, monitoring rapid changes in evapotranspiration, along with precipitation and soil moisture conditions, can provide early warnings of flash drought development.