Speaker: Dominik Schumacher, Lecturer at the Department of Environmental Systems Science, ETH Zurich

Title: Storylines of heat and drought

Abstract: The 2022 summer was unusually hot and dry across much of Europe. Soil moisture deficits were primarily invoked by precipitation shortages. This is, in turn, considered a manifestation of internal variability, and soil desiccation was further accelerated by warming-fuelled evaporation. More generally, unforced dynamics are considered the key meteorological driver of not just the hot and dry 2022 summer but also other extreme weather events. Human-induced climate change, on the other hand, is thought to modulate event intensity through thermodynamics. 

This perspective is useful and serves as the basis of conditional or storyline-based extreme event attribution approaches, but it also prompts questions: how does the role of thermodynamics change in the face of an ever-warming climate? Specifically, how would the 2022 summer unfold under additional background warming? How extreme would the already record-shattering 2021 Pacific Northwest heatwave become, and how would the severity of a drought such as in the Amazon in 2023 change? And just how defendable is the conceptual separation of thermodynamics and dynamics? 

To answer these questions, a suite of global Earth System model simulations is performed in which observed atmospheric circulation patterns are combined with different thermodynamic states.