Research

Regional Climate

Key Findings

Research at the Climate Impacts Group (CIG) has made significant contributions to our understanding of Pacific Northwest (PNW) climate variability and change. Key findings from this research include the following.

Characterizing PNW Climate Variability and Trends

The CIG has characterized PNW climate variability and trends, showing that:

• Warm-dry (cool-wet) winters in the PNW are associated with the warm (cold) phases of the El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO).
• PNW extreme weather events like wind storms, cold air outbreaks, and snow are strongly associated with the phase of the Pacific North America pattern, a large-scale predictable mode of natural climate variability (Brown 2003). This finding has contributed to the development of extreme events forecasts for the PNW.
• Most of the PNW has warmed steadily in the last 100 years at a rate of about 0.15° F (0.08°C) per decade, or 1.5 °F (0.83°C) per100 years. Precipitation has fluctuated but has generally increased over this time period (Figure 1) (Mote et al. 1999, Mote 2003).
• Springtime snow water equivalent in the mountains of the PNW (including British Columbia) has declined since the mid-20th century, a direct result of regional warming (Figure 1). The largest percentage declines occurred at lower elevations (Mote 2003).


Figure 1 20th century trends in (a, b) average annual PNW temperature and precipitation (1920-2000) and (c) April 1 snow water equivalent (1950-2000). These figures show widespread increases in average annual temperature and precipitation for the period 1920 to 2000 and decreases in April 1 snow water equivalent (an important indicator for forecasting summer water supplies) for the period 1950 to 2000. The size of the dot corresponds to the magnitude of the change. Pluses and minuses indicate increases or decreases, respectively, that are less than the given scale.

Paleo-climate Research

The CIG has placed 20th century PNW climate in broader context through paleo-climate research, showing that:

• The 1930s drought in the Columbia Basin was probably the second worst in the last 250 years, after that of the 1840s. (Gedalof 2002; Gedalof et al., 2004)
• The period from roughly 1800 to 1920 had lower interdecadal PDO variance than other times during a period of several hundred years (Figure 2) (Gedalof and Smith 2001; Gedalof 2002).
• The 1990s was the warmest decade of the last 154 years for March through October sea surface temperatures in the Strait of Juan de Fuca (Figure 4). Other warm periods occurred during 1870s, the 1900s, and the years from 1926 to 1934. These results are based on an innovative study using the internal growth rings in geoduck shells (Figure 3) to identify climate signals (Strom 2003).

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Figure 2 Comparison of the reconstructed (black) and observed (gray) PDO index. The reconstructed chronology in this figure is restricted to 1840-1990, the time common to the five climate reconstructions used for the composite reconstruction. Note the period of reduced variability from 1840 to approximately 1920. The time series is of the leading principal component, scaled to match the mean observed October to March PDO index (R=0.64).

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Figure 3 Geoduck clams. Geoducks are a species of long-lived (100+ years) large saltwater clams (Panope generosa) native to the northern Pacific coasts of Canada and the U.S. Pacific Northwest. Washington State’s Puget Sound bays and estuaries harbor the highest density of geoducks in the contiguous United States (Washington Dept. of Ecology). Photo courtesy of Are Strom. Used with permission.

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Figure 4 Observed and reconstructed March-October sea surface temperatures at Race Rocks Lighthouse, Canada. Reconstructed (solid red line) and instrumental (measured, solid blue line) March-October sea surface temperatures (degrees Celsius) at Race Rocks Lighthouse in the Strait of Juan de Fuca, 10 miles south of the southern tip of Vancouver Island. Reconstructed temperatures are developed from geoduck growth rings; 95% confidence intervals are indicated by the dashed red line. Data are missing in the instrumental series for the years 1940 and 1941.

PNW Climate Change

The CIG has examined how global climate change may affect PNW climate, finding that:

• Global climate models project mid- 21st century temperatures in the PNW that are well outside the natural range of temperature observed in the 20th century (Figure 5). They also suggest important changes in future precipitation: nearly all the climate models project wetter winters and drier summers in the 2020s and the 2040s (Mote et al. 2003). For more information see CIG’s Summary of Climate Change and Climate Change Scenarios.
• Statistical downscaling methods developed by CIG for temperature and precipitation can be (and have been) used to create datasets appropriate for driving hydrologic simulations in the PNW. CIG evaluated these methods for their ability to simulate the historic observed climate variability and streamflows. (Widmann et al. 2003; Salathé 2003; also Wood, A.W., Maurer, E.P., Kumar, A. and D.P. Lettenmaier, 2002, Long range experimental hydrologic forecasting for the eastern U.S. J. Geophysical Research 107(D20), 4429, doi:10.1029/2001JD000659).


Figure 5 Decadal mean changes in climate, referenced to twentieth century mean climate, over the Columbia River Basin for the 2020s (+ symbols), 2040s (diamonds), and 2090s (x's) from eight climate model scenarios. Large boxes bound the highest and lowest scenarios for each variable and decade. Features of twentieth century climate are also indicated in the lower part of the diagram: mean (asterisk), linear trend (arrow), range (ellipse shows +/- 2 sigma combined for both variables), and decadal means (boxes: 0 = 1900s, 1 = 1910s … 9 = 1990s).

Selected References

For more publications on PNW climate, please see CIG Publications.

Gedalof, Z., N.J. Mantua, and D.L. Peterson. 2002. A multi-century perspective of variability in the Pacific Decadal Oscillation: New insights from tree rings and corals. Geophysical Research Letters 29(24):2204. doi:10.1029/ 2002GL015824.

Mantua, N.J. 1999. The Pacific Decadal Oscillation and climate forecasting for North America. In Maryam Golnaraghi (ed), Climate Risk Solutions 1(1):10-13 (newsletter).

Mantua, N.J., and S.R. Hare. 2002. The Pacific Decadal Oscillation. Journal of Oceanography 58(1):35-44.

Mantua, N.J. and P.W. Mote (in review). The underlying rhythms: Characteristics of Pacific Northwest climate. Chapter 4 in E.L. Miles, A. K. Snover and The Climate Impacts Group, Rhythms of Change: An Integrated Assessment of Climate Impacts on the Pacific Northwest. Cambridge, Massachusetts: MIT Press.

Mantua, N.J., S.R. Hare, Y. Zhang, J.M. Wallace, and R.C. Francis. 1997. A Pacific interdecadal climate oscillation with impacts on salmon production. Bulletin of the American Meteorological Society 78:1069-1079.

Mote, P.W. (in review). Possible future climate. Chapter 5 in E.L. Miles, A. K. Snover and The Climate Impacts Group, Rhythms of Change: An Integrated Assessment of Climate Impacts on the Pacific Northwest. Cambridge, Massachusetts: MIT Press.

Mote, P.W. (2003). Trends in temperature and precipitation in the Pacific Northwest during the twentieth century. Northwest Science 77(4): 271-282.

Mote, P. W. 2001. Scientific assessment of climate change: Global and regional scales. Preparatory White Paper for Climate and Water Policy Meeting, Skamania, Washington, July 2001. Climate Impacts Group, University of Washington. 10pp.

Mote, P. and N.J. Mantua. 2002. Causes of climate variability in the Pacific Northwest. The Climate Report 3(2):2-6.