Revisiting Recent U.S. Heat Waves in a Warmer and More Humid Climate
We use a pair of high-resolution simulations with the Weather and Research Forecasting model (WRF) to investigate historic heat waves of the US. One simulation reproduces the weather and heat waves of the recent decades, the other is set up to reproduce that same weather, but in a significantly warmer and more humid climate as projected to occur under a high emissions scenario towards the end of this century. Investigating the differences, we find that dry heatwaves, which are common in the Western and Central US, become drier, while humid heatwaves tend to stay humid. Therefore, while heat stress – the combined impact of temperature and humidity on humans and ecosystems – increases everywhere due to the overall warming, this happens with regional nuances. Dry heatwaves becoming drier results in heat stress not increasing quite as severely as it could be, while such a relative dampening is absent in more humid regions. We also investigate the role of land-atmosphere coupling in contributing to these changes in heat wave characteristics.
The design of our experiments, with large‐scale atmospheric circulation, spectrally nudged, allows us to more robustly associate changes in heat wave characteristics to thermodynamic processes. Changes in dynamics, while probably not zero, appear to be of secondary importance when describing changes in future heatwaves and heat stress. This conclusion would justify focusing on better understanding and reducing uncertainties in thermodynamic changes for heatwaves and can help focus future research efforts.
Changes in future heatwave characteristics and associated heat stress over the US are found to be largely driven by thermodynamics, motivating a focus on better understanding and simulating the associated processes in coupled global and regional climate models.