17:00 UTC Tuesday, September 12
Emily Paterson, director – Model Product Management, RMS
Irma has now dissipated to the relief of many, not least those who experienced the storm’s wrath. The actuality of Irma was not nearly as bad as feared, as discussed in my colleague Tom Sabbatelli’s blog yesterday. Irma’s final path spared the major population centers of Miami and Tampa from the storm’s most damaging winds and storm surge.
Prior to and immediately after landfall, before we could see the final path and the actual impact of Irma, the best that anyone can do is look at the range of possible losses — as the final actual loss can only be known after an event is fully over and the details become clear.
To help our clients understand the potential magnitude of Irma’s insured loss during the storm’s approach, RMS provided guidance around what the distribution of potential wind losses looked like. But although we can have a good level of confidence in potential wind scenarios ahead of time, it is only part of the equation. As the hurricane approaches, we can provide guidance on the risk and identify areas that could be affected by storm surge and flooding, but the distribution of potential losses from these perils is uncertain as these losses are highly sensitive to the nuances of the storm’s final track and wind field structure.
Remember that the Saffir-Simpson scale no longer advises on the expected levels of storm surge following Hurricanes Katrina and Ike — storms that disproved the conventional understanding of the links between a hurricane’s intensity and its storm surge potential.
Now that Irma has gone, observations and imagery have started to come in that reveal the storm’s true impact. We are now able to shift our focus from “what could happen” to “what did happen”, from postulating potential wind loss distributions to delving into the hazard — including storm surge and flood — and damage observations to inform our final reconstructions of the event. Ultimately our understanding of the totality of losses from Irma will account for all loss drivers, including those which were too uncertain to estimate ahead of time. Storm surge, flood and other complicating factors, such as the evacuations, business interruption, and the prolonged and extensive power outages, among others, will all play a part in the final outcome.
While Irma has only dissipated very recently, what is already very clear is that Irma is a very complicated and complex event. How the interplay between wind, storm surge and flood plays out in terms of losses, and adding on top the impact of the complicating factors listed above, will ultimately dictate what the final losses will be.
Wind and surge observations from anemometers and gauges go a long way in helping us to better understand the hazard experienced on the ground, and are crucial as we look to reconstruct the hazard from Irma – our first step to understanding the full loss.
Satellite and drone imagery helps us go one step further and gives us a “birds eye view” of the damage experienced, helping to provide a fuller picture of both the type and level of damage, as well as a good indication of the extent. As we inspect the imagery we are looking for things that will help us refine our understanding of losses from this event — how far inland can we see surge damage? Is there roof damage from winds over a large area? We can use these observations to help refine and validate our understanding of loss. Another advantage of leveraging imagery is that it helps inform where we should focus our field reconnaissance efforts.
Figure 1. Map showing Key West Naval Base with photo image of residential area in the top right corner. Source: OpenStreetMap
Figure 2: Residential area near Key West Naval Base, pre-event image from Google Earth, post-event aerial image acquired by NOAA on September 11, 2017
Our “boots on the ground” field reconnaissance approach really helps us refine our understanding with more detailed information. Not only does it help validate hazard observations with damage observations, but conversations with home and business owners, as well as those working on the recovery efforts, gives us insight into the prolonged effects impacting the affected communities, such as lengthy closures of businesses and insight into the types of internal and contents damage experienced by homeowners. Our field reconnaissance plans are already underway and as those field observations come in, they will be fed into our process as well. The more information we have about the damage on the ground, the better our understanding of the full totality of losses from an event will be.