Fire · and the mudslide that follows
A wildfire strips a hillside of the roots that held it and bakes the soil so rain runs off instead of soaking in. The next hard storm can send that slope downhill as a debris flow — a fast river of mud, rock and burned trees. The U.S. Geological Survey models which burned basins will slide, and how badly. This maps that model, live. It is awareness, not a forecast, and it never says a place is safe.
Each marker is a fire the USGS has assessed for post-fire debris-flow hazard. Tap one to draw its burned drainage basins, each graded by the combined chance and size of a debris flow in a design storm. The grade is for a modelled rainstorm, not a live forecast — when rain actually threatens a burn scar, the warning comes from the NWS. Model & basins © USGS Emergency Assessment of Post-Fire Debris-Flow Hazards (ls/pwfdf) · burn severity MTBS · active fire NASA FIRMS · base © OpenStreetMap.
Behind the map — how the hazard is modelled
What burned
First, where the fire went and how hot. Satellites detect the active fire in near-real time (NASA FIRMS, from MODIS/VIIRS), and afterwards the burn is mapped by severity — lightly scorched to completely consumed.
Why it matters: the more severe the burn, the more water-repellent the soil and the more of the hillside is free to move. Burn severity is the first input to the debris-flow model.
NASA FIRMS · USGS/USFS MTBS
What will slide
For each burned drainage basin the USGS estimates the likelihood of a debris flow and its likely volume, then combines them into a hazard grade — Low, Moderate or High.
How it measures: a statistical model (fit to hundreds of real post-fire flows) takes the basin's steepness and shape, its burn severity, its soil, and a chosen rainfall intensity, and returns the odds. The map above reads the live USGS result, basin by basin.
USGS Landslide Hazards Program · ls/pwfdf
What sets it off
A fresh burn scar needs far less rain than open ground to fail — sometimes a single intense cell is enough. The National Weather Service watches the radar over burn scars and issues the debris-flow watches and warnings.
The number that matters is short-burst rainfall intensity (rain in 15 minutes), not the day's total — which is exactly what the USGS model is built around.
NOAA / National Weather Service
Recently assessed fires (live from USGS)
| Fire | Where | Assessed | Report |
|---|---|---|---|
| Loading the USGS assessments… | |||
Do not wait for a slide to start. When heavy rain is forecast over a recently burned slope above you, leave early and go to higher ground away from the drainage — debris flows move faster than a person can run and arrive with almost no warning. This page is a model and an explainer; the live warning comes from the official services.
A flood, a wave, a fire, a slide: they all end the same way, with families sent uphill and out, needing somewhere safe to shelter until they can go home or rebuild. That is not only an engineering question. It is an old human one — and there is an old, good answer.
Higher Ground — the oldest answer, and a request →