Catastrophe risk modeling firm AIR Worldwide (AIR) has released a physically based, probabilistic inland flood model for locations on and off the many and varied floodplains across the United States.

The AIR Inland Flood Model for the United States defines flood events based on a physical understanding of what causes flooding and how floods propagate through the country’s extensive river networks. The model captures inland flood risk for all 18 hydrological regions across the contiguous United States, an area of approximately 3 million square miles with a river network 1.4 million miles long, including 335,000 distinct drainage catchments, according to AIR.

Jayanta Guin
Jayanta Guin

[Dr. Jayanta Guin, who was appointed executive vice president of AIR Worldwide in April, discussed the difficulties of modeling flood risk and provided a preview of the model in an interview this summer. The model is the third one that AIR Worldwide has developed, following earlier inland flood models for Germany and Great Britain.]

The model simulates both the weather systems and the flooding they cause and accounts for a broad range of climatic conditions, snowmelt, local soil conditions, land use and topography. Its simulated flood propagation accounts for the effects of more than 20,000 lakes and reservoirs. Damage is determined by calculating the inundation depth at each affected location, taking into account the country’s extensive system of levees and their probability of failure, as well as regional differences in building codes and building practices.

In addition to accounting for flooding that will occur next to the river, AIR also incorporates flood hazard that can happen away from the river, known as off-floodplain flooding. This can happen because of factors such as particularly intense rainfall and poor drainage, among other factors.

AIR’s approach to simulating rainfall couples a global Community Atmospheric Model (CAM) with a regional Weather, Research, and Forecasting (WRF) model. The results are robust storm patterns over space and time. The model captures both large- and small-scale precipitation patterns, including the bursts of extreme rainfall that contribute greatly to highly localized flooding.

The AIR model also uses a physically based hydraulic model that calculates the extent of flooding and the depth of inundation at each location of interest on the floodplain. This model accurately accounts for local terrain characteristics and generates a physically consistent delineation of floodwater extents.

Guin said the industry has lacked the tools to effectively quantify flood risk in the U.S. In the release announcement, he said AIR’s new model is “game-changing” in its helping the industry manage this complex risk by better understanding the severity, frequency and location of potential flood events.

The AIR Inland Flood Model for the United States is currently available for Version 2.0 of the Touchstone and Version 16 of the CATRADER catastrophe risk management systems.

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