Atmospheric River Flood Risk Calculator
Translate forecast data into a quick flood probability score. Enter the integrated vapor transport, storm duration, antecedent soil saturation, and watershed area to gauge how likely an atmospheric river is to trigger flooding.
Understanding Atmospheric Rivers
Atmospheric rivers are long, narrow corridors of concentrated water vapor that transport enormous moisture from the tropics toward higher latitudes. When these invisible rivers make landfall, they can release sustained, intense rainfall, especially when terrain forces the air upward. Communities along the Pacific coasts, from California to Chile, know how these events can deliver months of precipitation in a matter of days. Because warmer air holds more moisture, climate change is expected to intensify atmospheric rivers, making tools that translate meteorological metrics into flood likelihood increasingly valuable.
Logistic Model Used by the Calculator
The calculator condenses four influential variables into a logistic probability model. The probability of flooding is defined as
where is a weighted sum of the inputs:
In this formulation is integrated vapor transport (kg m−1 s−1), is storm duration in hours, is soil saturation percentage, and is watershed area in square kilometers. The coefficients are illustrative, reflecting the tendency for high IVT, long duration, saturated soils, and broad drainage basins to accelerate flooding.
Sample Risk Categories
| Probability Range | Suggested Action |
|---|---|
| < 20% | Monitor forecasts and river levels |
| 20% – 40% | Review preparedness plans and supplies |
| 40% – 80% | Stage sandbags, alert residents, confirm drainage |
| > 80% | Activate emergency procedures and consider evacuation |
Integrated vapor transport above 500 kg m−1 s−1 is usually associated with strong events. When values exceed 1,000, forecasters often warn of widespread flooding. Duration and saturation modulate the effect: a long storm over already saturated soils can yield extreme runoff even if IVT is only moderate.
Continue analyzing hydrologic hazards with the flood recurrence interval calculator, the rainfall runoff calculator, and the coastal flood insurance calculator to pair atmospheric river assessments with broader flood planning.