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Augmentation and Use of WRF-Hydro to Simulate Overland Flow- and Streamflow-Generated Debris Flow Hazards in Burn Scars
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  • Chuxuan Li,
  • Alexander L Handwerger,
  • Jiali Wang,
  • Wei Yu,
  • Xiang Li,
  • Noah Joseph Finnegan,
  • Yingying Xie,
  • Giuseppe Buscarnera,
  • Daniel E Horton
Chuxuan Li
Northwestern University, Northwestern University

Corresponding Author:[email protected]

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Alexander L Handwerger
Jet Propulsion Laboratory, Caltech, Jet Propulsion Laboratory, Caltech
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Jiali Wang
Argonne National Laboratory (DOE), Argonne National Laboratory (DOE)
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Wei Yu
Weather Tech LLC., Weather Tech LLC.
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Xiang Li
Northwestern University, Northwestern University
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Noah Joseph Finnegan
University of California, Santa Cruz, University of California, Santa Cruz
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Yingying Xie
Purdue University, Purdue University
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Giuseppe Buscarnera
Northwestern University, Northwestern University
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Daniel E Horton
Northwestern University, Northwestern University
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Abstract

In steep wildfire-burned terrains, intense rainfall can produce large volumes of runoff that can trigger highly destructive debris flows. The ability to accurately characterize and forecast debris-flow hazards in burned terrains, however, remains limited. Here, we augment the Weather Research and Forecasting Hydrological modeling system (WRF-Hydro) to simulate both overland and channelized flows and assess postfire debris-flow hazards over a regional domain. We perform hindcast simulations using high-resolution weather radar-derived precipitation and reanalysis data to drive non-burned baseline and burn scar sensitivity experiments. Our simulations focus on January 2021 when an atmospheric river triggered numerous debris flows within a wildfire burn scar in Big Sur – one of which destroyed California’s famous Highway 1. Compared to the baseline, our burn scar simulation yields dramatic increases in total and peak discharge, and shorter lags between rainfall onset and peak discharge. At Rat Creek, where Highway 1 was destroyed, discharge volume increases eight-fold and peak discharge triples relative to the baseline. For all catchments within the burn scar, we find that the median catchment-area normalized discharge volume increases nine-fold after incorporating burn scar characteristics, while the 95th percentile volume increases 13-fold. Catchments with anomalously high hazard levels correspond well with post-event debris flow observations. Our results demonstrate that WRF-Hydro provides a compelling new physics-based tool to investigate and potentially forecast postfire hydrologic hazards at regional scales.