Collaborative Research: NSFGEO-NERC: Hurricane Risk Amplification and Changing North Atlantic Natural Disasters

This is a project jointly funded by the National Science Foundation’s Directorate for Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award recommendation, each Agency funds the proportion of the budget that supports scientists at institutions in their respective countries. It is a remarkable fact that hurricanes forming in the tropical Atlantic can pose a threat to the northeastern US and Western Europe, both well outside the tropics and on opposite sides of the Atlantic. The ability of hurricanes to inflict damage at such long range is well known in the US, with recent examples including Sandy in 2012 and Ida in 2021. On the other side of the basin Ophelia (2017) and Leslie (2018) caused severe damage in Ireland, Portugal, and Spain. Such storms are a natural topic for collaboration between NSF and NERC given their transatlantic impacts. Research under this award seeks to understand the Atlantic hurricanes that make landfall at higher latitudes, taking into account their full lifecycle and impacts. Lifecycle is an important consideration as hurricanes can transform considerably as they encounter the cool ocean surface, frontal temperature contrasts, and upper-level ridges, troughs, and jet streams of the middle latitudes. By the time a hurricane makes landfall in Ireland or New York, it is likely to have undergone at least a partial transition from the warm core, vertically aligned structure of a tropical cyclone to the cold-core, westward-tilted structure and larger areal extent of an extratropical cyclone. The lifecycle transitions of these hurricanes complicate efforts to understand and predict their behavior and anticipate changes in their frequency and intensity due to climate variability and change. Changes in hurricane structure also create important differences in impacts, for instance storms which retain their tropical characteristics at landfall are typically more damaging, but storms which have largely transformed into extratropical cyclones are considerably more common. They can also create disruptions over a wider area, as was the case with Hurricane Sandy. A key challenge in work on hurricanes at higher latitudes, referred to here as cyclones of tropical origin (CTOs), is scarcity of observations, as CTOs occur infrequently and the observed record is relatively short. This project takes advantage of several archives of model simulations which substantially augment the observations, including ensembles of seasonal forecasts from the European Centre for Medium-range Weather Forecasts. The forecast ensembles contain many examples of CTOs which could have happened but did not, thus boosting the sample size for CTOs from perhaps 3 per year to 300 per year. The project also uses specialized models to look at hurricane impacts, including a high-resolution coastal ocean model to simulate storm surge and a hydrological model for flooding. The project has societal value due to its emphasis on hazardous weather events. The project includes a concerted effort to provide actionable guidance to decision makers. The ensembles available from seasonal forecasts and other model outputs allow consideration of a wider variety of CTOs than have occurred in the observational record, thus better representing the range of possibilities. The application of storm surge and flood models to these simulated storms provides further guidance on the range of possible CTO impacts. The range of possible storms and their impacts is synthesized in the form of storylines, which are narrative descriptions of the events and their impacts to be used for planning purposes. The project supports a postdoctoral researcher, thereby promoting the future workforce in this research area. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.