Flash droughts: a review and assessment of the challenges imposed by rapid onset droughts in the United States

Authors: OTKIN, J. - University Of Wisconsin; SVOBODA, M. - University Of Nebraska; HUNT, E.D. - Atmospheric And Environmental Research; Anderson, Martha; HAIN, C. - Collaborator; BASARA, J. - University Of Oklahoma

Submitted to: Bulletin of the American Meteorological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2017
Publication Date: 5/1/2018
Citation: Otkin, J., Svoboda, M., Hunt, E., Anderson, M.C., Hain, C., Basara, J. 2018. Flash droughts: a review and assessment of the challenges imposed by rapid onset droughts in the United States. Bulletin of the American Meterological Society. 99: 911-919. https://doi.org/10.1175/BAMS-D-17-0149.1.
DOI: https://doi.org/10.1175/BAMS-D-17-0149.1

Interpretive Summary: The term "flash drought" is a relatively new addition to our lexicon for describing meteorological events. While drought is typically considered to be a slow onset process (as opposed to floods), there are times when drought impacts can appear quite suddenly, with crop conditions degrading rapidly over periods of a week or two. These flash - or rapid onset - droughts can be devastating to growers, allowing little time for adaptation or mitigation and often leading to significant yield loss. It is therefore important that we better understand the processes and conditions that trigger flash droughts, and to develop effective early warning indices. Recently, however, there have evolved two different definitions to describe these drought events: the first focuses more on duration (short-lived droughts), while the second stresses the rapid onset characteristic. This paper argues that the latter is the more relevant feature as it applies to the unique challenges faced by stakeholders, who have less time to prepare for adverse effects when drought develops so quickly. We propose that a definition of flash drought focusing on the rate of drought intensification be adopted within the scientific community.

Technical Abstract: Given the increasing use of the term “flash drought” by the media and scientific community, it is prudent to develop a consistent definition that can be used to identify these events and to understand their salient characteristics. It is generally accepted that flash droughts occur more often during the summer due to increased evaporative demand; however, two distinct approaches have been used to identify them. The first approach focuses on their rate of intensification, whereas the second approach implicitly focuses on their duration. These conflicting notions for what constitutes a flash drought (e.g., unusually fast intensification versus short duration) introduce ambiguity that affects our ability to detect their onset, monitor their development, and understand the mechanisms that control their evolution. Here, we propose that the definition for flash drought should focus on its rate of intensification rather than its duration, with droughts that develop rapidly identified as flash droughts. There are two primary reasons for favoring the intensification approach over the duration approach. First, longevity and impact are basic characteristics of drought. This means that short-term events lasting only a few days and having minimal impacts are inconsistent with the general understanding of drought and therefore should not be considered flash droughts. Second, by focusing on the rate of intensification, the proposed flash drought definition highlights the unique challenges faced by vulnerable stakeholders who have less time to prepare for adverse effects when drought develops so quickly.