NSFGEO-NERC: HUrricane Risk Amplification and Changing North Atlantic Natural disasters (Huracan)

Lead Research Organisation: University of Reading
Department Name: Meteorology


Tropical cyclones (TCs) are one of the most dangerous natural hazards on Earth. Known as hurricanes in the North Atlantic, TCs represent ~30% ($75bn) of global annual losses due to all natural hazards, to which all our societies are - at least economically - exposed. Understanding future changes in TC frequency and strength are active, challenging and critical research areas. The term 'tropical' suggests that the lifetime and impacts of TCs are confined to the tropics, but this is not the case. Some tropical cyclones (TCs) migrating into the mid-latitudes retain the physical characteristics of a hurricane, while others structurally evolve into post-tropical cyclones (PTCs). Both types (which we collectively call CTOs) can be extremely intense and their hazards set them apart from typical extratropical cyclones, the type of storm our societies are adapted to in mid-latitudes.

Recent events, and ongoing research, have brought into sharp focus the dangers posed by CTOs to the North-East United States (NEUS), as well as the British Isles and Western Europe (BIWE). North of 30N, events in the last ten years have been the most costly on record, causing loss of life and widespread severe damage: Ophelia totalled $70m in Ireland; Sandy alone totalled US$17bn in New York City; Henri and Ida in autumn 2021 caused $31-44bn in losses around New York State. More generally, and despite uncertainty due to decadal variability, there are indications that the number of CTOs reaching the midlatitudes has increased, consistent with projections of CTOs making landfall in BIWE, in the future. Future projections, despite uncertainties, highlight the increasing likelihood of a CTO landfall over BIWE/NEUS. Even if such events should be rare, the potential consequences are alarming; for instance, our homes and infrastructure are not designed to resist hurricane-intensity winds, nor the associated flooding. Although our weather-forecasting centres surveil tropical weather, our early-warning systems remain largely untested against CTOs.

Risk assessment is held back by a fundamental lack of information: while some UK and US records exist as far back as 1860, the US National Hurricane Center only began recording non-US landfalls in 1991 and a complete analysis of TCs east of 30W only in 2005. Very little research exists for the eastern side of the Atlantic. According to analysis of 7 reanalysis datasets since 1979, 3-5 CTOs reach NEUS and 1-2 CTOs reach BIWE each year.

How can we address these shortcomings? Continued surveillance (e.g. with new satellite products) is key. Complementing observations are model data, for instance the climate 'reanalyses', typically spanning the last 50-100 years. Additionally, we need far more physically plausible evidence, and physical reasoning, for robust risk assessment.
Huracán will:
1. make use of the latest developments in numerical simulation, with 1-3km grid-spacing (similar to the concept of pixel size in a digital camera) enabling us to fundamentally change how we simulate the processes leading to the birth (genesis) of CTOs.
2. tap into a wealth of potential case studies contained in ensembles of seasonal prediction model simulations, which offer multiple versions of 'could-have-been' CTOs and augment the sample size by a factor of order 100.
3. combine all the data products in 1) and 2) to construct plausible physical routes (storylines) for a CTO landfall and to identify what the worst-case scenarios could be in terms of wind, storm surge, precipitation (both leading to extreme flooding) and enable future planning.

Huracán will leverage state-of-the-art capabilities (theory, simulation, process analysis) across leading institutions on both sides of the Atlantic, and harness international collaborations to address two pivotal issues: (i) the key factors that influence the formation and evolution of CTOs reaching the midlatitudes; (ii) what governs mid-latitude landfall of the most hazardous CTOs.


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