If a wildfire is followed by an intense rainstorm, this causes further ecological damage for without vegetation to cushion the rainfall, water runoff can become very fast-moving leading to a highly destructive landslide. Such events have been increasing across recent years, as a consequence of climate changes.
The term for this is “debris flow,” and it can be damaging to cars, homes and roadways. There is also a risk to human life. An example of such an event was the 2021 debris flow that tore out a 150-foot section of roadway. This took place along Highway 1 near Big Sur, California, U.S.
To help to predict whether these dangerous landslides are likely to occur, researchers at Northwestern University have come up with a physics-based numerical model to investigate and predict areas susceptible to debris flows. These are areas based around so-termed ‘high hazard’ zones.
The new model can accurately predict landslides along wildfire burn scars. The researchers hope the simulations will become an early warning system for people living in high-risk areas. To test out the strength of the model, the researchers validated the model-simulated hydrological conditions using soil moisture and streamflow observations.
For the model, the researchers adapted a hydrology model to simulate how rainwater moves over burned areas. The resulting model demonstrates which areas are more likely to experience debris flows based on vegetation, topological features and where it rains hardest.
The model shows how regions burned by wildfires are more susceptible to debris flows, a type of fast-moving, destructive landslide. In addition, the simulation found that burned areas cause water to flow much faster and in greater volumes compared to unburned land. To add to this risk, in some regions, waxes from burned vegetation melts, enters the soil and then solidifies. These waxes create a barrier for rain, blocking it from penetrating the soil. Instead, rain runs over the top of the soil, picking up rocks, mud, trees and even cars to become a debris flow.
Commenting on the model, lead researcher Daniel Horton outlines where the model is in the development process and what the model is capable of providing. He says: “Although it’s not yet to operational standards, this modelling framework could one day be instrumental in forecasting where debris flows are likely to occur and deciding who needs to be evacuated.”
He adds: “An advantage of our model is that it uses precipitation as it would fall in the real world…We’re simulating spatially complex and time-evolving precipitation and how that precipitation interacts with the land surface.”
The research features in the journal Natural Hazards and Earth System Sciences. The research is titled “Augmentation of WRF-Hydro to simulate overland-flow- and streamflow-generated debris flow susceptibility in burn scars.”
