Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Collaborative Specialization

Hazards, Risks, and Resilience

Supervisor

Najafi, Reza M.

Abstract

Atmospheric rivers (ARs) are narrow bands of concentrated moisture that account for approximately 90% of poleward water vapor transport from the tropics. Landfalling ARs generate intense precipitation that contributes to coastal water supply but can also lead to severe flooding. ARs can trigger and intensify other natural processes such as snowmelt and soil moisture, leading to Compound inland flooding (CIF) events. These include rain on snow (ROS) events, when rain causes significant snowmelt amplifying runoff, and saturation excess flooding (SEF) events, when rain falls on saturated soil and the decreased infiltration amplifies runoff. In a nonstationary climate, AR events are projected to increase in both frequency and intensity. Despite implications for compound events, ARs are often studied in a univariate context, which risks underestimating the severity of AR events and hinders hazard mitigation efforts. This study characterizes AR relationships with other hazards to investigate how they contribute to CIF events, specifically ROS and SEF events. Using the CanRCM4 single model initial-condition large ensemble dataset, the frequency and seasonality of AR-driven CIF events is determined for Western North American coastal areas in historical and future periods, while focusing on how ARs interact with additional factors such as snowpack and soil moisture. Internal variability is quantified and assessed using the signal to noise ratio to determine the relative strength of projected trends. ARs were found to contribute up to 90% of CIF events in coastal areas and some orographic areas. Additionally, this relationship is expected to grow stronger in warmer climates, especially for ROS events. The findings underscore the importance of considering environmental factors in AR-related flooding risks for flood management strategies and infrastructure design to adapt to a changing climate.

Summary for Lay Audience

Narrow bands of dense concentrated air moisture movement account for a large amount of global water transport. When these bands of moisture reach land, they often generate intense rain or snow fall. In Coastal Regions, these storms are key contributors to local water supply, however, they are also key contributors to major floods. The rainfall can often interact with environmental factors, like snowmelt or soil moisture, increasing total runoff generated. Over time, increases in greenhouse gas emissions can cause an increase in overall mean temperature by better retaining heat from the sun. This process is referred to as climate change, and it has varying effects on different regional climates and atmospheric processes. The effects of climate change may include increases in the frequency and intensity of severe moisture transport that results in intense rainstorms. These storms are often only studied in relation to rainfall or economic damages, ignoring how they interact with other environmental factors. This approach risks underestimating the severity of moisture transport related storms especially in the context of climate change. This hinders disaster response planning and infrastructure design efforts. Therefore, this study focuses on examining moisture transport within the context of related environmental factors and their potential to cause flooding potential in the Western North America Coastal region. Furthermore, how this relationship may be impacted by climate change is also examined, while identifying potential uncertainties within future climate predictions. Results are generated using climate model simulated present and future climate conditions. The findings highlight the importance of integrating moisture transport related flooding risks into flood management strategies and infrastructure design to adapt to a changing climate.

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