Regionalization and trends in winter precipitation in the northwestern USA

Abstract

Recent modeling studies have predicted that while temperature is expected to increase over the next few decades in the Pacific Northwest (PNW), model predictions of winter season precipitation are highly variable. Implications of potential climate change were explored by regionalizing PNW climate. Using rotated Principal Components Analysis (PCA), sub-regions within the PNW were developed for winter season precipitation from 1895-2003. Analyses include synoptic discussions based on trends of the time series of the component scores as well as an examination of the sensitivity to the El Niño/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) for each sub-region. Four sub-regions during the winter season were created, based on temporal variability of precipitation. While previous studies suggest that there is regional coherence in PNW precipitation, analysis of the time series of the component scores for each sub-region suggests otherwise. Several sub-regions show widely diverging trends in winter season precipitation over the past 30 yr, a period that also coincides with significant warming across the PNW. Differences in the sign and strength of correlations between ENSO and the PDO with winter season precipitation occur between the subregions, which further suggests a lack of coherence in the PNW. © Inter-Research 2007.