ERC Advanced Grants at D-USYS: Heini Wernli and the INTEXseas project

People remember extreme events such as storm Lothar in 1999 or the flooding in Switzerland in 2005. Such exceptional events that last just a few days can typically be traced back to certain weather systems. But what if entire seasons exhibit extreme values? At a seasonal level, there is no simple association with a specific weather event – it generally takes a whole sequence of unusual events.

Hitherto unexplored timescale

Heini Wernli’s INTEXseas project thus looks into the warmest or wettest summer, spring, autumn or winter in a particular place. As one of his research questions he looks into which sequence of weather events creates an extraordinary season. And how do the narratives differ, for example about the wettest winter in different areas around the world? While the wettest winter in Britain is perhaps just a series of low pressure systems, in Algeria a single Mediterranean storm is enough to make the winter the wettest on record. The physicist first looks into this question using global data from the last fifty years in order to identify the main weather systems that lead to extreme seasons in the current climate.

Climate simulations over 1000 years

In a second part of the INTEXseas project, some of Wernli’s team members work together with the group of Reto Knutti, Professor of Climate Physics at the Institute for Atmospheric and Climate Science. Using very large ensemble simulations with a global climate model, the researchers extend their study of extreme seasons to future climate conditions. This ensemble approach helps identifying and understanding the characteristics and dynamics of the hottest, coldest, wettest, driest etc. seasons and how these extremes change as a result of climate change. This central part of the project will provide information on where in the world the wettest seasons, for example, will become much wetter in the future - and why; is it because normal precipitation systems are becoming more intense or more frequent – or because new types of precipitation systems are emerging?

Impact on the economy and society

When something happens meteorologically that the public has not yet experienced, this can have great socio-economic consequences. As part of this project, Wernli will therefore also cooperate with David Bresch, Professor for Weather and Climate at the Institute for Environmental Decisions. In a third part of the INTEXseas project, they plan to investigate a number of socio-economically relevant seasonal weather constellations. For example, could there be an entire winter without enough snow for skiing in a traditional ski resort? A winter without snow fall that is at the same time too warm to be able to produce artificial snow?

Research out of curiosity

Currently, Wernli and three postdocs are working on INTEXseas. Two doctoral students are expected to join them in one year’s time. Thanks to the ERC Advanced Grant, it is possible to work with a team of experienced scientists. «This is unique», Wernli emphasises. «As a team of specialists with complementary competencies, we can hit the ground running». The five-year perspective of the European Research Commission is another advantage. This also comes with a lot of responsibility and a huge amount of trust. Heini Wernli is looking forward to this challenge and stresses «curiosity is an important driving force for my research». He and his team will work hard to obtain novel insight into the processes that lead to extreme seasons.