"What if" scenarios drive many of the most important questions in catastrophe modeling: "What if a Category 5 hurricane makes landfall near Tampa?" "What if a magnitude 9.0 earthquake strikes off Canada's Vancouver Island?" However, "what if" scenarios do not have to focus solely on events that may happen in the future; they can also reflect on those that happened in the past-and what their present day impacts would be.
Scenarios of future events are based on our best understanding of what might happen, while historical events-particularly those in the relatively recent past-provide us with highly reliable depictions of real world examples of physical processes and their effects on the built environment.
Catastrophe models allow us to answer the intriguing question, "What if a past event were to happen today?" In the case of U.S. hurricanes, answering this question helps expand our understanding of storms and their impact, whether for ones in the "distant" past (the 1900 Galveston Hurricane, for example) or in the more recent past (2005's Hurricane Katrina).
For events in the distant past, not only has the built landscape evolved but the natural environment has potentially changed significantly as well, which has a particularly pronounced impact when examining storm surge risk. The creation or destruction of barrier islands and other coastal morphologic processes could significantly alter storm surge elevations and pathways. Rapid changes in the built environment can significantly alter storm surge effects for recent storms as well. For example, the enhancement and expansion of the coastal defense system around New Orleans following Hurricane Katrina represents a major alteration to how surge will affect the region when the next hurricane strikes.
Complex dynamics such as the effect on losses of rapid increases in coastal exposure, building code enhancements, and changes in coastal geography can only be quantified by a model that provides a robust depiction of the winds and atmospheric pressure within the hurricane environment, a high resolution depiction of coastal and inland land elevation, and a detailed, yet flexible, representation of the many variations within the building inventory. Occupancy type, building height, construction materials, and many other details are essential in determining how much damage hurricane winds and storm surge will inflict on a structure.
The AIR U.S. Hurricane Model provides risk modelers with all the tools needed to obtain an all-encompassing view of hurricane risk,enabling them to learn from the past and prepare for the future. AIR's historical event sets include approximately 80 historical tropical cyclone events for the continental United States; each is a faithful representation of a major historical storm. AIR releases historical event sets for a variety of perils, including inland floods, earthquakes, severe thunderstorms, and winter storms, for a variety of regions. These historical "recreations" answer the question "what if"-that is, what would my losses be were these major events to reoccur today.