In the last century, average temperatures have risen in the Pacific Northwest and models predict additional increases over the next decades. The Office of the Washington State Climatologist (2024) recorded a 3.3 °F increase in Washington and a 3.6 °F increase in Oregon since 1924. The University of California MERCED Climatology Lab’s Multivariate Adapted Constructed Analog Future Time Series Tool (2024) modeled an average summer temperature increase of 2.4 °F for a low greenhouse gas scenario and 3.7°F for a high greenhouse gas scenario in Washington by 2040 and 2.3 °F for a low greenhouse gas scenario and 2.9°F for a high greenhouse gas scenario in Oregon. Precipitation is predicted to increase overall but decrease during the summer. Reduced snowpacks that melt earlier will reduce summer stream flows and increase the frequency and severity of floods and droughts. The soil moisture available on July 1 will decline throughout the North Cascades by up to 35 percent by the 2040s (Elsner et al. 2010). Increased evaporation and transpiration, with decreased soil moisture, will reduce forest species’ growth, vigor, and survivorship (Raymond et al. 2022). Increased wildfires and insect outbreaks will alter forest structure and composition (Halofsky 2020; Agne 2018; Flannigan et al. 2000).
