Making sense of flash drought: definitions, indicators, and where we go from here

Abstract

The topic of “Flash Drought” is rapidly gaining attention within both the research and drought management communities. This literature review aims to synthesize the research to-date and provide a basis for future research on the topic. Specifically, our review is focused on documenting the range of definitions of “flash drought” being proposed in the research community. We found that the term first appeared in the peer-reviewed literature in 2002, and by 2020 has become an area of active research. Within that 18-year span, “flash drought” has been given 29 general descriptions, and 20 papers have provided measurable, defining criteria used to distinguish a flash drought from other drought. Of these papers, 11 distinguish flash drought as a rapid-onset drought event while eight distinguish flash drought as a short-term or short-lived, yet severe, drought event and one paper considers flash drought as both a short-lived and rapid onset event. Of the papers that define a flash drought by its rate of onset, the rate proposed ranges from 5 days to 8 weeks. Currently, there is not a universally accepted definition or criteria for “flash drought,” despite recent research that has called for the research community to adopt the principle of rapid-intensification of drought conditions.

Global Flash Drought Monitoring Using Surface Soil Moisture

“…The retrospective temporal averaging of SMS for 30-days reduces the transient variability in SMS 30 (compared to SMS) and helps capture the rootzone dynamics of the soil profile across different hydroclimates (Gao et al, 2019;Manfreda et al, 2014;Sure & Dikshit, 2019). The selected temporal window of 30 days used in the development of SMS 30 and RRD is consistent with the timescales of development of flash droughts reported by Pendergrass et al (2020) and Lisonbee et al (2021).…”

Development of a Flash Drought Intensity Index

“…These variables are typically chosen because they capture the main drivers and impacts of moisture-related vegetation stress. Most of the studies identify flash drought using a set of thresholds requiring a minimum rate of intensification over a certain period of time [36]. These definitions are consistent with recommendations in the flash drought review article by [1]; however, most are unable to quantify the intensity of the flash drought.…”

Global Flash Drought Analysis: Uncertainties From Indicators and Datasets

“…Although the purpose is to ensure comparability among the datasets, some influence of these underlying differences could still impact the results, in particular, for locations with varying topography, vegetation types, bodies of water, and along coast lines. In addition, due to limited scope, this study only compares two of the many indicators so far used in past studies to define flash drought (Lisonbee et al, 2021), which is why more research is needed to compare various other indices for exploring the related similarities and discrepancies among them. The findings can be further extended to explore a more robust indicator of flash drought that efficiently couples the rapid soil-moisture depletion rates in deeper layers with changes in atmospheric evaporative demand, and develop suitable forecasting tools focused on their direct implication on vegetation health (Pendergrass et al, 2020).…”