Flash Drought Characteristics and Prediction

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 define a flash drought event as a drought event with more than (or equal to) two categories degradation in a 4-week period based on the U.S. Drought Monitor (USDM). We examine the characteristics of flash drought events, their temporal and spatial distributions, and distinctions from conventional, slowly-evolving droughts based on rasterized USDM data from 2000 to 2017. We also identify a list of major flash drought events and investigate the causes leading to the rapid development using concurrent Phase 2 of the North American Land Data Assimilation System (NLDAS-2) data. Unlike conventional droughts mainly driven by precipitation deficits, anomalously high evapotranspiration (ET) rates, caused by anomalously high temperatures (e.g., during heatwaves) and/or anomalously high incoming radiation, are usually present before the onset of flash droughts. As a result, monitoring rapid changes in ET, along with precipitation and soil moisture, can provide early warnings of flash drought development. An experimental tool was created at NOAA's Climate Prediction Center (CPC) to predict the areas vulnerable for flash drought development using near real-time NLDAS-2 monitoring data, and has been used to support the operational production of CPC's Monthly Drought Outlook since April 2018. We will briefly introduce the tool, evaluate its performance during the 2018 warm season, and outline next steps.