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

Abstract

<p>The topic of “Flash Drought” has rapidly gained attention within the research and drought management communities within the last decade. In preparation for a recent workshop on Flash Drought, the National Integrated Drought Information System (NIDIS) prepared a literature review to synthesize the research to-date (as of August 2020) and to provide a basis for future research on the topic. Specifically, this review is focused on documenting the range of definitions of "flash drought" that have been proposed by the research community. 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, 19 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 or rapid-intensification drought event while seven 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. Currently, there is no 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. This topic was further explored at the NIDIS-sponsored Flash Drought Workshop on 1-3 December 2020, where additional perspectives were shared about the key characteristics of flash drought that should inform its definition.  We will provide a review of the literature-derived definitions as well as a brief overview of this additional discussion.</p>

Global Flash Drought Monitoring Using Surface Soil Moisture

“…The calculation of SPEI is based on the estimates of accumulated water deficit/surplus at different timescales based on climatic water balance and adjustment to a log‐logistic probability distribution. SPEI is increasingly used in flash droughts studies as it is sensitive to both heatwave and precipitation‐deficit flash droughts by accounting for both ET and precipitation anomalies—a key advantage over other univariate drought indices (Hunt et al., 2014; Lisonbee et al., 2021; Noguera et al., 2021). For this study, we use global monthly SPEI at 1‐month accumulation timescale (SPEI‐1) as an indicator of transient meteorological drought from April 2015‐December 2018 at 0.5° (50‐km) spatial resolution (from SPEIbase‐version 2.6, Beguería & Vicente Serrano, 2020).…”

“…Flash droughts are characterized by three S's: Speed, Severity, and Spread, i.e., rapid intensification of drought to severe levels over a large area (Christian et al., 2019; Lisonbee et al., 2021; Otkin et al., 2018). These fast‐evolving droughts are associated with large‐scale agricultural losses (Jencso et al., 2019; Jin et al., 2019), expansive wildfires (Christian et al., 2020), and potential challenges for seasonal and sub‐seasonal climate predictions (Pendergrass et al., 2020).…”

Global Flash Drought Analysis: Uncertainties From Indicators and Datasets

“…So far, FDs have been defined based on several indicators, such as evaporative stress ratio (ESR) (Christian, Basara, Otkin, & Hunt, 2019; Christian, Basara, Otkin, Hunt, et al., 2019; Otkin et al., 2018), soil moisture estimates (Mahto & Mishra, 2020; Mukherjee & Mishra, 2022; V. Mishra et al., 2021; Yuan, Zheng, et al., 2019), the U.S. Drought Monitor (Chen et al., 2019; Svoboda et al., 2002), Evaporative Demand Drought Index (Parker et al., 2021), and Standardized Precipitation Index (Lisonbee et al., 2021; Noguera et al., 2021). In this study, we selected standardized ESR (SESR) and root‐zone‐soil‐moisture (RZSM) to define FDs due to their overwhelming use in recent years (Lisonbee et al., 2021; Pendergrass et al., 2020). Both SESR and soil‐moisture have been applied globally for defining FDs (Christian et al., 2021; Koster et al., 2019).…”

Spatio-temporal evolution of wet–dry event features and their transition across the Upper Jhelum Basin (UJB) in South Asia

“…Flash drought is a relatively new type of drought. Currently, there is not a universally accepted definition or criteria for flash drought, though there is general consensus on the principle of rapid onset or intensification characterized by moisture deficits and abnormally high temperatures for a period lasting at least 3 weeks (Lisonbee et al, 2021;Otkin et al, 2018;Hunt et al, 2009). This highlights the usefulness of SPEI at the monthly scale in representing flood and flash drought events.…”