Study shows ‘summer of the century’ characterised by late-onset heat and drought under current climate conditions
The summers of recent years have been hot, but not unusual from a meteorological perspective. According to researchers at Leipzig University, though, the next extreme summer would far exceed anything we have experienced so far.
To be prepared for this, it is important to understand what a ‘summer of the century’ might look like in the current climate. This is precisely what researchers at Leipzig University have investigated in a new study.
They found that late summer is now warming up significantly more than early summer, and that the soil tends to be drier than in previous summers. “As a result, there is now a longer period in late summer during which favourable weather conditions, combined with very dry soil, can lead to extreme and prolonged heat,” says the study’s lead author, Dr Peter Pfleiderer from the Institute for Meteorology at Leipzig University, summarising one of the study’s findings. It has just been published in the specialist journal Earth’s Future.
Through their analysis of ‘summers of the century,’ the researchers show that the changes generally expected in summer are even more pronounced during these rare, extreme summers. At the same time, the increase in temperatures in European summers is greater than in other parts of the world. The study shows just how intense prolonged heatwaves can become in the current climate, and how people, local authorities and society as a whole should adapt.
In the pre-industrial climate (1850 to 1900), summers were very warm throughout the entire season, as Pfleiderer says. The researchers found that ‘summers of the century’ in today’s climate could start off relatively cool and then remain consistently very hot throughout mid- and late summer. “We also show that, both for summers in general and for extreme and rare summers, hot days tend to occur more frequently in the current climate, thereby increasing the likelihood of prolonged heatwaves,” explains the climate researcher.
Extreme heat is closely linked to dry soil. When favourable weather conditions cause a region to warm up, some of the energy is used for the evaporation of water. However, once the ground is dry, the energy is converted solely into heat that can be felt, and temperatures can rise dramatically. “Until now, it has not been possible to investigate the impact of drier soils on heat during ‘summers of the century,’ as the available simulations were insufficient for the statistical analysis of such rare events. Here we show that the changes we observe for average summers would be significantly more pronounced in once-in-a-century summers,” explains Junior Professor Sebastian Sippel from Leipzig University. He is the last author of the study.
Researchers at Leipzig University have begun carrying out climate simulations using a method known as rare-event sampling. With rare-event sampling, many simulations begin at the start of summer. Checks are carried out on a regular basis to see whether the simulations develop into hot summers. If this is not the case, the simulations are terminated early in order to save computing time. “This meant that, with manageable computing costs, we were able to simulate many very hot summers in both the current and pre-industrial climates. These simulations then made it possible to investigate how ‘summers of the century’ have changed beyond the general warming trend,” reports Pfleiderer.
Researchers at Leipzig University will continue to study extreme summers in Europe. They want to find out how changes in atmospheric circulation have affected extreme summers. They also want to investigate how ‘summers of the century’ have changed in other regions of Europe. For example, it is to be expected that in the Mediterranean region or in Eastern Europe, the significant factors will be different to those in Central Europe.
- Originaltitel der Veröffentlichung in „Earth´s Future“: „Heat extremes in hot summer seasons intensify more than in average summers under global warming”
