A scale to characterize the strength and impacts of atmospheric rivers

TitleA scale to characterize the strength and impacts of atmospheric rivers
Publication TypeJournal Article
Year of Publication2019
AuthorsRalph FM, Rutz J.J, Cordeira JM, Dettinger M, Anderson M., Reynolds D., Schick L.I, Smallcomb C.
JournalBulletin of the American Meteorological Society
Volume100
Pagination269-290
Date Published2019/02
Type of ArticleArticle
ISBN Number0003-0007
Accession NumberWOS:000461196200008
Keywordsalgorithm; california; connection; cyclones; events; extreme precipitation; landfalls; Meteorology & Atmospheric Sciences; satellite; water-vapor transport; west-coast precipitation
Abstract

Atmospheric rivers (ARs) play vital roles in the western United States and related regions globally, not only producing heavy precipitation and flooding, but also providing beneficial water supply. This paper introduces a scale for the intensity and impacts of ARs. Its utility may be greatest where ARs are the most impactful storm type and hurricanes, nor'easters, and tornadoes are nearly nonexistent. Two parameters dominate the hydrologic outcomes and impacts of ARs: vertically integrated water vapor transport (IVT) and AR duration [i.e., the duration of at least minimal AR conditions (IVT >= 250 kg m(-1) s(-1))]. The scale uses an observed or predicted time series of IVT at a given geographic location and is based on the maximum IVT and AR duration at that point during an AR event. AR categories 1-5 are defined by thresholds for maximum IVT (3-h average) of 250, 500, 750, 1,000, and 1,250 kg m(-1) s(-1), and by IVT exceeding 250 kg m(-1) s(-1) continuously for 24-48 h. If the AR event duration is less than 24 h, it is downgraded by one category. If it is longer than 48 h, it is upgraded one category. The scale recognizes that weak ARs are often mostly beneficial because they can enhance water supply and snowpack, while stronger ARs can become mostly hazardous, for example, if they strike an area with antecedent conditions that enhance vulnerability, such as burn scars or wet conditions. Extended durations can enhance impacts. Short durations can mitigate impacts.

DOI10.1175/bams-d-18-0023.1
Short TitleBull. Amer. Meteorol. Soc.
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