Flash Drought Occurrence Across the United States
Flash droughts are extreme events characterized by the rapid onset and development of drought conditions. The impact of flash drought in agricultural regions can be devastating, as rapid depletion of root zone soil moisture and increasing moisture stress adversely affect vegetation health and can lead to significant yield loss. The evaporative stress, the ratio between evapotranspiration and potential evapotranspiration, is a reliable indicator of flash drought. Using the evaporative stress is advantageous for flash drought analysis as the evaporative stress is directly a function of (or inherently contains information of) near-surface air temperature, wind speed, vapor pressure deficit, total atmospheric flux (latent and sensible heat fluxes), as well as soil moisture and precipitation. If extreme atmospheric anomalies (i.e., lack of rainfall, warm surface temperatures, strong winds, and clear skies) persist for several weeks, the onset of flash drought can occur rapidly. This study presents a methodology for flash drought identification applied across the United States using the North American Regional Reanalysis. The Standardized Evaporative Stress Ratio (SESR) was used to determine whether drought conditions existed, while the change in SESR was used to satisfy the “flash” component, or the rapid rate of intensification, of drought. The results presented will show the “hot spots” of flash drought occurrence across the United States, the partitioning of flash droughts into intensities, and flash drought “aftershocks”.