Investigating the uncertainties surrounding the future of extreme extratropical cyclones, specifically in the North Atlantic Ocean

Abstract

The climate is changing, and we must understand how this will alter risks associated with extreme weather events. One of the most impactful weather types in the UK is an extratropical cyclone (ETC). Intense ETCs can cause significant damage from heavy precipitation and strong winds, leading to extensive flooding
and damage to infrastructure, causing loss of life in extreme cases.

After decades of research, there remains low confidence in how ETCs will respond to climate change, especially in the North Atlantic Ocean. The purpose of this thesis is to increase this confidence, explore the driving mechanisms, and understand the changes in meteorological extremes.

First, a novel tracking algorithm is used to explore historical and future ETC
statistics. ETC statistics are compared to two other commonly-used tracking algorithms and show good agreement for extreme ETC intensities but poor agreement for ETC frequencies.

Second, how changes to a climate model can influence the simulation of ETCs
and extreme precipitation are examined. Motivated by recent results on the potential importance of the stratosphere, this is studied by systematically changing the vertical resolution of an intermediate-complexity climate model. Specifically, the change in ETC biases from changing vertical resolution is compared with the change in ETC statistics from a typical climate scenario. The climate change signal is found to be larger than that from increasing vertical resolution.

Finally, a state-of-the-art climate model, designed with UK climate in mind, is
used to assess the most recent projections of ETCs. While no climate change signal was present for extreme surface wind speeds, the number and intensity of ETCs were found to increase in the British Isles. While both mean and extreme precipitation in ETCs increased, it was found that extremes increased more substantially. Therefore, the UK needs to prepare for future increases in damages from ETCs.

Date of Award	23 Jan 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Dann M Mitchell (Supervisor), William Seviour (Supervisor) & Paul J Valdes (Supervisor)