Atmosphere Dynamical Processes and Soil moisture Feedbacks associated with accelerating heatwave trends

Europe has been identified as a Heatwave hotspot in two important ways. Firstly, temperatures warm faster than over most regions globally (Rousi et al. 2022, Vautard et al. 2023), secondly the hottest temperatures increase significantly faster compared to more moderate temperatures (Kornhuber et al. 2024, Patterson 2023). Large scale atmosphere dynamical patterns have been suggested to be associated with these trends, such as an increase in double jet patterns (Rousi et al. 2022), trends in circumglobal Rossby waves (Teng et al. 2022) and local high pressure systems (Vautard et al. 2023).

In this talk we reflect on the fact that climate models underestimate these trends. We show that during persistent circulation regimes, typically present during quasi-stationary Rossby waves (Kornhuber et al. 2023, Luo et al 2021) or double jets (Liu et al., in prep.), models underestimate the heatwave response. We link this to model biases in a three-way feedback process between temperature, high-pressure and soil moisture, which becomes active after a threshold in soil moisture and temperature is crossed (Tian et al. in prep.). We provide evidence that models substantially underestimate this process which is particularly important in driving changes in most extreme heat events over humid to semi-arid regions globally.