First Advisor

Paul Loikith

Date of Award


Document Type


Degree Name

Bachelor of Science (B.S.) in Physics: Environmental Physics and University Honors






Atmospheric circulation, Climatology -- Mathematical models, Hydrologic models -- Pacific Northwest




The hydroclimatology of the Pacific Northwest is characterized by wet winters and dry summers; however, the end of the rainy season is subject to considerable year-to-year variability. Early onset of the dry season can introduce challenges for water resource managers. Historically, anomalously dry springs are the result of persistent atmospheric ridging, with notable examples in May 2015 and 2018. As climate change may affect the persistence and frequency of ridges, it is important to understand potential changes in springtime ridging. Future changes will have implications for the length of the rainy season and consequently freshwater availability throughout the region. Therefore, the historical climatology of springtime atmospheric ridging is characterized through a focus on persistence and frequency. A ridge index is developed to identify anomalous springtime ridging events relevant to the Portland, Oregon region of the Pacific Northwest. Resulting trends and potential systematic changes in ridge characteristics are discussed, including several notable periods of ridging occurring over the last decade. The ridge index is applied to ten CMIP6 climate models and finds reasonable model fidelity in simulating historical ridging climatology. The ridge index is then applied over the mid- and late-century periods to project future ridging frequency and persistence. Results show slight decreases in ridging persistence and frequency over time. The lack of future change in atmospheric ridging likely means that water resources will not be significantly impacted by prematurely ended rainy seasons due to ridging; however, heat-related impacts will likely be more severe in the future due to climate change.


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