16-9 An Improved Model for Predicting Postfire Debris-Flow Volume in the Western United States

Session: Wildland Fire: An Agent of Geomorphic, Ecologic, and Societal Change

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Authors:

Abstract:

Methods for predicting debris-flow volume are a critical component of postfire debris-flow hazard assessments and are used to estimate the magnitude of postfire debris-flow sediment volumes in the western United States. However, most current postfire debris-flow volume models are trained to predict volume in a specific area (e.g., southern California) and are less accurate when applied to regions outside of their calibration dataset. This limits model applicability in postfire hazard assessment frameworks designed for widespread use and underscores the need for a broadly applicable postfire debris-flow volume model to improve hazard assessments. We introduce a new empirical model that better predicts postfire debris-flow volume across the western United States compared to existing models. Specifically, we develop a multiple linear regression model that predicts postfire debris-flow volume as a function of rainfall, watershed terrain, and fire characteristics using a dataset of 227 volumes collected from 34 burn areas across six states. This model improves on existing volume models, as it uses a rainfall anomaly metric to normalize regional differences in rainfall characteristics and was developed using a more geographically diverse training dataset. As a result, it can accurately predict postfire debris-flow volume in multiple geographic regions using a single regression equation. Results show that the new volume model outperforms three regional models, including a model that is widely used in current postfire hazard assessments, in several scenarios. For instance, it outperforms existing models against the entire western United States dataset and matches or exceeds existing model performance in the regions for which they were developed (southern California, the Intermountain West, and the interior Southwest). The new model also performs well in data-limited regions that lack the volume data to develop region-specific volume models, such as the Sierra Nevada and Pacific Northwest. The broad applicability and consistent performance of the new debris-flow volume model makes it a promising tool for improving postfire hazard assessment in the western United States.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9217

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