Publication Date

2025

Document Type

Dissertation/Thesis

First Advisor

Michaelis, Allison C.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geographic and Atmospheric Sciences

Abstract

Atmospheric rivers (ARs) are long, narrow bands of water vapor transport that are commonly associated with a low-level jet ahead of a cold front of an extratropical cyclone. When multiple ARs occur in succession of one another within a certain aggregation period, it is known as an AR family. ARs and AR families are important to the U.S. West Coast—and especially California’s—hydroclimate, providing both beneficial and hazardous precipitation to the region. Recent studies have suggested that not all ARs and, thus, AR families, respond similarly to a warming climate. Therefore, it is critical to better understand how climate change impacts AR families in the future. This study examines a recent sequence of landfalling ARs from 26 December 2022 through 19 January 2023 in present-day and potential future environments using the Model for Prediction Across Scales – Atmosphere (MPAS-A) version 8.0. During this period, a family of nine ARs made landfall in California, producing about half of California’s mean annual precipitation. Heavy rain and snow over this three-week period were beneficial in building the snowpack across the mountainous regions and alleviating drought conditions in several areas; however, flooding, mudslides, and power outages were also common occurrences, underscoring the beneficial vs. hazardous nature of ARs. Results show that MPAS-A was able to simulate an AR family that compared well with reanalysis data during the first 10 days of the simulation. The present-day MPAS-A simulation replicated seven distinct ARs making landfall in Northern California with a mean AR scale of ~2, a total of ~240 hours of AR conditions, and a mean maximum IVT of ~730 kg m–1 s–1 across all individual IVT pulses. In the future simulation, only six ARs made landfall in Northern California, yet the mean AR scale in the future simulation was ~4, a total of ~270 hours of AR conditions occurred, and the mean maximum IVT was more than 1100 kg m–1 s–1 across all pulses. Furthermore, a future climate intensified the precipitation over several watersheds and shortened the timing between events, effectively reducing the recovery time between onshore impacts. Last, our results indicate that, due to overall warmer temperatures in a future climate, more accumulated precipitation in the future simulation fell as rain rather than snow, leading to more ARs in the future contributing to snow melt, rather than snow accumulation. Ultimately, our results provide an outlook on a future climate for the U.S. West Coast that can assist policy makers, water managers, agriculture specialists, and private entities create plans to prepare for and mitigate potential risks that may arise with stronger ARs and AR families in the future.

Extent

67 pages

Language

en

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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