CR2025_01 Understanding the risk of extreme U.S. winter weather

Lead Supervisor: Andrew Charlton-Perez, Department of Meteorology, University of Reading

Email: a.j.charlton-perez@reading.ac.uk

Co-supervisors: Christopher O’Reilly, Department of Meteorology, University of Reading; Alec Vessey, AXA XL

The United States is particularly vulnerable to extreme winter weather, and in February 2021, December 2022, and January 2024, the U.S. was devastated by extreme cold. The Feb. 2021 winter weather event was among the costliest extreme weather events to occur globally in 2021, causing US$ 27.2bn in economic damage. This event was a particular shock for the Insurance Industry, and damages greatly surpassed the previous most costly severe winter weather event in 1993 (US$ 12.2bn) (Figure 1). At the time, the 2021 event was widely reported in the media as ‘Storm Uri’ (e.g., Independent, 2021; Mail Online, 2021, The Weather Channel, 2021), but the devastation was caused by a Cold Air Outbreak (CAO) rather than a low-pressure storm. Cold air formed in Canada and progressed southward over the U.S., and resulted in widespread power outages, business interruption, property damage, and fatalities. Freeze was experienced across the U.S. (Figure 2), but damage was especially high in the southern U.S. states such as Texas, which are not regularly exposed to such temperature extremes.

Damaging CAOs have occurred over the U.S. in the past, such as the 1993 event, which was termed the “Storm of the Century” and caused US$ 12.2bn in economic loss (Figure 1). However, following a CAO ‘drought’ between 2001 and 2011, the unprecedent extent of damage caused by the events in 2021, 2022 and 2024 have shocked society, and particularly the insurance industry. Considering these recent extraordinary events, there are open questions as to how these CAOs developed to become so costly, is an even more devastating CAO or another CAO ‘drought’ possible in future years, and is climate change impacting the frequency and severity of such events? Using a newly developed CAO tracking algorithm, such questions can now be investigated and communicated to decision-makers to help mitigate the consequences of such events.

CAOs and extra-tropical windstorms are the main drivers of economic and insured losses in the U.S. during wintertime. These events are collectively combined in the insurance industry as ‘U.S. Winterstorms’, which describes any event that causes damage by wind, freeze, ice, and snow. However, in the scientific literature, these hazards are often reported upon separately as they are distinct meteorological phenomenon. This diversity in risk inducing weather phenomena makes it particularly challenging to have a complete view of risk from extreme U.S. winter weather, which limits our ability to mitigate and protect against consequences.

This PhD project seeks to ascertain the collective risk of ‘U.S. Winterstorms’ in the present-day and future climate whilst also advancing the understanding of the risk posed by U.S. extra-tropical storms, CAOs and other extreme winter weather phenomena that can cause damage. This project also aims to exploit this improved meteorological understanding of extreme U.S. winter weather together with exposure and vulnerability datasets to fully understand the societal consequences and risk of such weather events. With supervisory support from AXA XL, a global (re)insurance company, findings will have real-world applicability and help insurance companies mitigate the consequences of extreme U.S. winter weather more effectively, whilst also delivering high-impact research that is applicable to many other industries and that answers key scientific gaps in knowledge.

This project has three core research objectives:

1. Quantify the collective present-day risk of extreme U.S. winter weather (extra-tropical storms, CAOs and other weather phenomena), and determine the sensitivity to various methods used to identify such hazards in historical datasets.
2. Determine how ‘extreme’ the Feb. 2021 U.S. Cold Air Outbreak was and examine the synoptic-development of this and other significant extreme U.S. winter weather events.
3. Assess how the frequency and severity of extreme U.S. winter weather may change in a future climate in response to climate change.

Training opportunities:

The PhD student will have regular support from AXA XL, a global (re)insurer, and the opportunity to train in the application of Catastrophe modelling. The student will spend a 3-month secondment within AXA XL’s London-based Science and Natural Perils Team, to develop skills in risk analysis within a business setting.

They will benefit from the rich experience of the well-established Reading researchers, from the supervisory team and other research groups at the University. The student will be encouraged to attend domestic and international academic conferences and workshops. Training for writing scientific and public-oriented publications will also be provided.

Student profile:

This project is suitable for a numerate, enthusiastic, and motivated student, with an interest in furthering our scientific understanding of U.S. Cold Air Outbreaks (CAO) and other winter weather phenomena, and also how risks is quantified / mitigated against within the (re)insurance industry. A degree involving a substantial level of numeracy would be beneficial, such as physics, mathematics, engineering, or a related environmental or physical science. Some experience of using Linux and programming software would be beneficial, or a willingness and drive to learn these skills.

Co-Sponsorship details:

The project will receive a CASE award from AXA XL.