Publication Date

2025

Document Type

Dissertation/Thesis

First Advisor

Michaelis, Allison C.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geography and Atmospheric Sciences

Abstract

Postfire debris flows can occur when surface-water runoff dislodges and carries a slurry of loose sediment and vegetation downslope, usually in steep, recently burned terrain. Short-duration, high-intensity rainfall embedded within short or long-duration rainstorms (e.g., thunderstorms and atmospheric rivers) is most commonly associated with this mode of debris-flow initiation. The typical horizontal grid spacings of global numerical weather prediction and general circulation models are too coarse to resolve these convective precipitation features, which poses an obstacle to short-term forecasting and investigating future trends in the frequency, magnitude, and characteristics of debris-flow generating rainfall. For this study, 15-minute precipitation and simulated reflectivity from a set of dynamically downscaled, convective-permitting simulations (~3.75 km) are used over two time periods—historical (1990–2005) and late-century (2085–2100)—to assess the convective characteristics associated with postfire debris-flow triggering across Northern California, Southern California, and Colorado. In the historical simulation, the results show regional and seasonal differences in radar reflectivity signatures with some areas and seasons (e.g., Northern California during the cool season) experiencing more linear modes and others (e.g., Colorado during the warm season) dominated by cellular modes. In the late-century simulations, a substantial increase in postfire debris-flow precipitation threshold exceedances is found. Linear mode increases in Northern and Southern California, particularly in the more extreme climate change scenario, are observed. California’s future increase in linear mode is also coupled with an increase in the areal extent of intense precipitation. Understanding the changing characteristics of precipitation that triggers postfire debris flows is important to the development of mitigation and adaptation strategies to protect communities vulnerable to the effects of this cascading hazard.

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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