Seasonal Climate Variability and Change in the Pacific Northwest of the United States

Abstract

Observed changes in climate of the U.S. Pacific Northwest since the early twentieth century were examined using four different datasets. Annual mean temperature increased by approximately 0.68-0.88C from 1901 to 2012, with corroborating indicators including a lengthened freeze-free season, increased temperature of the coldest night of the year, and increased growing-season potential evapotranspiration. Seasonal temperature trends over shorter time scales (,50 yr) were variable. Despite increased warming rates in most seasons over the last half century, nonsignificant cooling was observed during spring from 1980 to 2012. Observations show a long-term increase in spring precipitation; however, decreased summer and autumn precipitation and increased potential evapotranspiration have resulted in larger climatic water deficits over the past four decades. A bootstrapped multiple linear regression model was used to better resolve the temporal heterogeneity of seasonal temperature and precipitation trends and to apportion trends to internal climate variability, solar variability, volcanic aerosols, and anthropogenic forcing. The El Niño-Southern Oscillation and the PacificNorth American pattern were the primary modulators of seasonal temperature trends on multidecadal time scales: solar and volcanic forcing were nonsignificant predictors and contributed weakly to observed trends. Anthropogenic forcing was a significant predictor of, and the leading contributor to, long-term warming; natural factors alone fail to explain the observed warming. Conversely, poor model skill for seasonal precipitation suggests that other factors need to be considered to understand the sources of seasonal precipitation trends.

Swiss Needle Cast in Western Oregon Douglas-Fir Plantations: 20‐Year Monitoring Results

“…Spring and summer precipitation has been increasing approximately 2%-3% per decade [28]. These linear changes in winter temperature and spring precipitation are consistent with the epidemiology factors that increase disease pressure.…”

“…In general, winter temperature has been steadily increasing with the mean annual temperature in the Pacific Northwest (PNW), which has increased 0.2˝C per decade [28]. Spring and summer precipitation has been increasing approximately 2%-3% per decade [28].…”

Atmospheric controls on northeast Pacific temperature variability and change, 1900–2012

“…Other studies have quantified smaller (≤50%) circulation influences (18, 32, 33) on western US warming, but in many cases dynamical forcing is inferred from detrended circulation proxies (33)(34)(35)(36), including the PDO, or indices representing atmospheric conditions in the central North Pacific [e.g., the NPI (18,33) or the Pacific-North American (PNA) pattern (32,34)]. Detrended indices are unsuited to capture dynamical changes, and we find generally stronger coastal temperature relationships with NE Pacific SLP1 than with the NPI or PNA (Table S2).…”

Indian time: time, seasonality, and culture in Traditional Ecological Knowledge of climate change

“…Natural scientists have demonstrated significant changes in climate (e.g., Abatzoglou et al 2014) and some consequences of those changes (e.g., Dalton et al 2013). Native American communities are also recognizing change (Charnley et al 2007;Alexander et al 2011).…”