Augmentation and Use of WRF-Hydro to Simulate Overland Flow- and
Streamflow-Generated Debris Flow Hazards in Burn Scars
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.