A global-scale overview of precipitation-deficit flash droughts

Abstract

Flash droughts are defined as fast and intense dryings of the land system. In these episodes, declines in precipitation deficits are often accompanied by rapid intensifications of evaporative demand, leading to sharp soil moisture decreases and noticeable agricultural and environmental impacts. This research presents a straightforward framework for global historical characterization of precipitation-deficit-related flash droughts, examining the extent to which this type of hazard can be described using only pentad rainfall data. The Drought Exceedance Probability Index was applied to global gridded high-resolution rainfall data for 1979 - 2020. Sharp upsurges in the pentad index series were detected and counted to analyze the occurrence of precipitation-deficit flash droughts. The precipitation characteristics associated to flash drought incidence were explored to learn if some rainfall regimes or times of the year are more prone to the phenomenon, which could help societies become more prepared for the risk. It was observed that climates with marked inter-annual and intra-annual rainfall variability record more flash droughts, especially when that variability is significant during the local wet seasons. This is the case of regions with erratic rainfall generation mechanisms such as Mediterranean climates or monsoon climates. The episodes mainly occur during what is expected to be the humid time of the year, when they can produce greater impact. The methodology used was able to detect the most intense events described in previous studies that used variables associated to soil moisture dryness, confirming the role of acute precipitation deficits in triggering them.