California has a good chance of experiencing the sort of 'super-storm' usually seen only in disaster movies, according to the US Geological Survey.
It could produce up to 10 feet of rain, overwhelm the state’s flood-protection system and cause more than $300 billion-worth of damage, flooding up to a quarter of houses in the state.
The ARkStorm Scenario is based on prehistoric geologic flood history in California, combined with with modern flood mapping and climate-change projections.
"The ARkStorm scenario is a complete picture of what that storm would do to the social and economic systems of California," says Lucy Jones, chief scientist of the USGS Multi-Hazards Demonstration Project and architect of ARkStorm.
"We think this event happens once every 100 or 200 years or so, which puts it in the same category as our big San Andreas earthquakes. The ARkStorm is essentially two historic storms (January 1969 and February 1986) put back to back in a scientifically plausible way. The model is not an extremely extreme event."
The team created a series of statewide landslide susceptibility maps, the most detailed ever produced. They also developed the first physics-based coastal storm modeling system for analyzing severe storm impacts both as they could impact today and under various climate-change and sea-level-rise scenarios.
"The ARkStorm report will prove to be another invaluable tool in engaging the whole of our community in addressing flood emergencies in California," says FEMA Region IX director Nancy Ward.
"It is entirely possible that flood control infrastructure and mitigation efforts could be overwhelmed by the USGS ARkStorm scenario, and the report suggests ways forward to limit the damage that is sure to result."