About Pacific Northwest Climate

Climate Impacts in Brief

This page provides a comprehensive but brief overview of the impacts of climate variability and change on the Pacific Northwest (PNW):

A summary of projected changes in major drivers (e.g., temeprature, precipitation, sea level rise) of Pacific Northwest climate change impacts is available here in PDF format (version date: March 2012). This summary table was prepared by the CIG for the Washington Department of Ecology's ongoing adaptation planning efforts.

Impacts of Natural Climate Variability on PNW Climate

El Niņo/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) are important factors for PNW climate due to their influence on atmospheric circulation over the North Pacific and North America. Analysis of past ENSO and PDO events shows that:

These connections between ENSO and PDO and PNW climate are useful, since they allow us to predict regional climate a few seasons to a year in advance. However, ENSO and PDO are not the sole drivers of PNW climate. Even with perfect predictions of ENSO and PDO, about 70% of the region’s winter climate variability remains unexplained. Other climate patterns, combined with “noise” and the chaotic nature of climate system, also contribute.

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Impacts of Natural Climate Variability on PNW Resources

Even subtle changes in PNW precipitation and temperature have noticeable impacts on the region’s mountain snowpack, river flows and flooding, the likelihood of summer droughts, forest productivity and forest fire risk, salmon abundance, and quality of coastal and near-shore habitat.

El Niño conditions in the PNW increase the chances for: Warm PDO conditions in the PNW increase the chances for:
Lower than average mountain snowpack
(see figure 1)
Lower than average salmon returns
Lower than average streamflow (see figure 1) Forest fires
Fewer floods (see figure 2 ) Increased tree growth, seedling establishment, and forest productivity at higher elevations
Lower quality coastal and near-shore marine habitat Decreased tree growth, seedling establishment, and forest productivity at lower elevations
Drought  
Conflict over water resources  
Coastal erosion  
La Niña conditions in the PNW increase the chances for: Cool PDO conditions in the PNW increase the chances for:
Higher than average mountain snowpack
(see figure 1)
Higher salmon returns
Higher than average streamflow (see figure 1) Fewer forest fires
Flooding (see figure 2) Decreased tree growth, seedling establishment, and forest productivity at higher elevations
Higher quality coastal and near-shore marine habitat Increased tree growth, seedling establishment, and forest productivity at lower elevations
fewer droughts  
Landslides  
Coastal flooding  

click images to enlarge

[graph] Impacts of ENSO and PDO on snowpack at specific locations in the PNW[graph] Impacts of ENSO and PDO on streamflow at specific locations in the PNW

Figure 1 Impacts of ENSO and PDO on (a) snowpack and (b) streamflow at specific locations in the PNW. Average total winter snow depth is shown for the winter season (January 15 to April 15) at Snoqualmie Pass, Washington. Streamflow is for April-September average flow on the Columbia River at The Dalles after removing the effects of the dams on streamflow. Averages are computed during the warm phases (white) and cool phases (black) of ENSO and PDO separately and combined. Note the cumulative effect when ENSO and PDO are in-phase (i.e., El Niño and warm phase PDO, La Niña and cool phase PDO). Percent changes from normal winter snow depth and summer streamflow associated with ENSO and PDO show that El Niño and/or warm PDO winters tend to have lower than average snowpack and streamflow. The reverse is true for La Niña and/or cool PDO.

click image to enlarge

[graph] Influence of Climate Variability on PNW Flooding

Figure 2 Influence of climate variability on PNW flooding. Figure 2 illustrates how the probability of flooding in the PNW varies with ENSO and PDO phases. The results are based on analysis of long (57-65 years) streamflow records from 26 unregulated river basins (i.e., those without dams) throughout the PNW. The probability of flooding was defined as the probability that the observed daily streamflow exceeded the mean annual flood at least once during the year. There is a clear overall trend from low to high probability of flooding across the climate categories from warm PDO + warm ENSO (El Niño) to cool PDO + cool ENSO (La Niña) conditions.

click image to enlarge

[graph] The influence of ENSO and PDO on the seasonal evolution of average snow depth at Snoqualmie Pass, Washington.

Figure 3 The influence of ENSO and PDO on the seasonal evolution of average snow depth at Snoqualmie Pass, Washington. Average snow depth for cool and warm phases of ENSO (top) and ENSO and PDO together (bottom), versus date. In El Niño years, snow depth generally stops increasing at the end of January, whereas in La Niña years, it grows until mid-March. When both ENSO and PDO are in phase (cool or warm), snow depth is considerably higher (if both are in cool phase) or lower (when both are in warm phase) than average.

Because it is currently possible to forecast climate conditions a few seasons to a year in advance, it’s also possible to forecast PNW streamflow conditions a few seasons to a year in advance. Using seasonal streamflow forecasts could increase hydropower production and revenues (Hamlet et al. 2002), improve flood control, and improve instream flow conditions for fish. The CIG is also working to develop other climate-based resource forecasts for salmon fisheries and forest resources.

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Impacts of Climate Change on PNW Climate

During the next 20-40 years, the climate of the PNW is projected to change significantly. 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. They also suggest important changes in future precipitation: most climate models project wetter winters and drier summers in the 2020s and the 2040s (Mote et al. 2009).

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Impacts of Climate Change on PNW Resources

As a result of human-caused climate change (“global warming”), the PNW is likely to see:

Changes in water resources

Changes in salmon

Changes in forests

Changes along the coasts

Summary of Changes in the Region

The following series of figures (figure 4) ranks the potential impacts of climate change (for the 2040s) according to our confidence in the projected impacts and our estimation of their relative importance for the Pacific Northwest as a whole.

The arrows indicate the relative magnitudes (small, medium, or large) of the ecological and/or socioeconomic impacts that climate change would have on the region as a whole, and whether the impacts would be positive or negative. This ranking accounts for the magnitude of the climate impact itself (either quantified or estimated) and the estimated magnitude of its regional consequence. For example, conflicts over water resources are expected to increase, which would be a negative impact of climate change.

Impacts are categorized by high, medium, or low confidence levels, loosely based on the IPCC's definitions of these terms (Intergovernmental Panel on Climate Change (IPCC). 1996. Impacts, Adaptations and Mitigations of Climate Change: Scientific-Technical Analyses. Contribution of Working Group II to the Second Assessment Report of the Intergovernmental Panel on Climate Change. R. T. Watson, M. C. Zinyowera, and R. M. Moss (eds.). New York: Cambridge University Press.).

Global map, Warm Phase PDO

Figure 4 Impacts of Climate Change on the Pacific Northwest

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