Differences in physical drivers of diurnal and nocturnal summer heat waves

Heat waves place a large burden on society. There are differences in the societal impact between diurnal heatwaves and nocturnal heatwaves. The latter in particular places stress on humans and animals, where exceeding the thermal comfort level may lead to heat-related deaths. Climate change affects not just the mean temperature, but also occurrences of exceptional warmth. We postulate that climate change has a different effect on the occurrence of diurnal and nocturnal heatwaves.

Heat waves are extreme events that, by definition, don’t occur frequently. To study extreme events and to be able to robustly do statistical analyses, we use the large ensemble KNMI-LENTIS. This way, we don’t have to rely on statistical interpolation to have enough events to study. KNMI-LENTIS is a time-slice large ensemble generated with the global climate model EC-Earth3. It consists of 2 time slices: the present-day climate and a future climate that is +2K warmer than the present-day. Each time slice consists of 1600 years.

We investigate the formation and ending of different types of summer heat waves in north-western Europe. Making the distinction between nocturnal, diurnal and compound heat waves allows us to disentangle the physical processes that drive the different types. Particularly we focus on advection and large-scale processes on the one hand, and local processes based on land-atmosphere coupling feedback mechanisms on the other hand.