Atmospheric Rivers as Drought Busters on the U.S. West Coast

TitleAtmospheric Rivers as Drought Busters on the U.S. West Coast
Publication TypeJournal Article
Year of Publication2013
AuthorsDettinger, MD
JournalJournal of Hydrometeorology
Volume14
Start Page1721
Abstract

Atmospheric rivers (ARs) have, in recent years, been recognized as the cause of the large majority of major
floods in rivers all along the U.S. West Coast and as the source of 30%–50% of all precipitation in the same
region. The present study surveys the frequency with which ARs have played a critical role as a common cause
of the end of droughts on the West Coast. This question was based on the observation that, in most cases,
droughts end abruptly as a result of the arrival of an especially wet month or, more exactly, a few very large
storms. This observation is documented using both Palmer Drought Severity Index and 6-month Standardized
Precipitation Index measures of drought occurrence for climate divisions across the conterminous United
States from 1895 to 2010. When the individual storm sequences that contributed most to the wet months that
broke historical West Coast droughts from 1950 to 2010 were evaluated, 33%–74% of droughts were broken
by the arrival of landfalling AR storms. In the Pacific Northwest, 60%–74%of all persistent drought endings
have been brought about by the arrival of AR storms. In California, about 33%–40% of all persistent drought
endings have been brought about by landfalling AR storms, with more localized low pressure systems responsible
for many of the remaining drought breaks.

DOI10.1175/JHM-D-13-02.1