Flash drought is characterized by a rapid rate of onset and intensification within a few weeks. It usually accompanies exhausted soil moisture and high-temperature stress and exerts detrimental impacts on the growth of crops and the ecosystem. However, the global occurrence characteristics of flash drought in the recent four decades remain unclear. This study analyzes the spatiotemporal variability of flash drought identified by rapid decreases in the standardized evaporative stress ratio (SESR) from 1981 to 2020 and investigates their meteorological drivers. Results show that the flash drought mainly occurred in middle and low latitude areas. The coverage of flash drought showed a statistically significant decrease during 1981-2020. With the year of 2000 as a turning point, the coverage of flash drought trend reversed from a significant decline to a significant rise. Flash drought has no noticeable seasonal change. With the increase of the intensity of flash drought, the proportion of flash drought gradually decreased. Slight flash drought (FD_1; 50.9 %) is seven times of extreme flash drought (FD_4). The analysis of the evolution of hydro-meteorological variables concurrent with the global flash drought shows that flash drought was more triggered by abnormally low precipitation, soil moisture, evapotranspiration, and high temperature. In addition, the anomaly gradually increases with the increase of intensity. Water deficit is an important factor affecting the occurrence of flash drought, and only 10.9 % of flash drought events occurred in both positive soil moisture and precipitation anomalies. The results reference future research on flash drought on various spatial scales under a changing climate.
Keywords: Flash drought; Meteorological condition; Spatiotemporal variability; Standardized evaporative stress ratio.
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