Five centuries of U.S. West Coast drought: Occurrence, spatial distribution, and associated atmospheric circulation patterns

Abstract

AbstractThe U.S. West Coast drought commencing in 2012 developed in association with a large, persistent high‐pressure ridge linked to internal atmospheric variability. This study places the occurrence, spatial patterns, and associated circulation features of West Coast drought into a paleoclimate context through a synoptic dendroclimatology approach linking atmospheric circulation to surface hydroclimate patterns. Spatial reconstructions of upper atmosphere pressure patterns and cool‐season drought show that West Coast‐wide drought, although relatively rare compared to north‐south dipole drought, has occurred periodically since 1500 Common Era and is consistently associated with a strong ridge centered along the Pacific Northwest coast. Atmospheric blocking is also linked to north‐dry dipole droughts, while south‐dry and wider Western droughts indicate La Niña‐type patterns. The transition latitude between the northern and southern sides of the western precipitation dipole, important for California hydroclimate patterns, has had frequent year‐to‐year fluctuations but remained centered on 40°N over the past five centuries.