Emma Holmberg: The predictability of European temperature extremes and their health impacts under global change

Abstract

Extreme temperature events can cause severe disruptions to society, from negative health consequences to infrastructure damage. Heat action plans, including early warning systems, are a key element in the mitigation of such impacts. Here we investigate the predictability of temperature extremes and their associated health impacts in Europe, in the context of our changing climate. We first investigate the predictability of temperature extremes from a theoretical standpoint, leveraging techniques from dynamical systems theory to quantitatively assess atmospheric persistence. Our results show a regionally and tropospheric-level dependent relationship between warm temperature extremes and atmospheric persistence. We then assess the practical predictability of hot and cold temperature extremes utilising sub-seasonal reforecast data, and the aforementioned measure of persistence. We demonstrate atmospheric persistence informing on practical predictability, measured here by forecast skill, in some cases, again with marked seasonal variation. Furthermore, local processes appear to play an important role in the endgenderment of, and forecast skill for, temperature extremes. Next, we apply methods from epidemiology to temperature forecasts, to produce heat-related mortality forecasts for 2022 and 2023. We find that heat-related mortality can, on average, be forecasted skilfully up to approximately one week. However, we emphasise the increased forecast skill in Iberia associated with the record-breaking temperatures experienced in 2022. Finally, we assess the role of changes in atmospheric circulation patterns for heat-related mortality. We note that changes in the dynamics of the atmosphere can play a reinforcing role to that of the thermodynamic warming trend, such as during the European summer of 2003. These findings could help inform the development of fit-for-purpose heat warning systems. Collectively, this thesis highlights the value in combining theoretical, and impact-focused approaches, for predicting extreme temperatures and their associated health impacts. This is imperative for society’s broader effort to adapt to a warmer climate.