Similarity-based storylines of future climate extremes in Switzerland

The heatwave of 2003, the flooding of 2005, the drought of 2018, or the snow-scarce winter of 2019/2020 are vivid examples of extreme weather events affecting Switzerland. The CH2018 climate scenarios for Switzerland show that such kind of events will become more intense in the future, depending on the future emission pathway and the considered time horizon. So far, CH2018-based information is typically communicated as changes in the mean or extremes of a climate variable, including the uncertainty of these changes. Presenting information in this manner is scientifically correct, but not tangible for everyone. Interested stakeholders often have difficulties to imagine what the future climate, and in particular how future extreme conditions might look like.

To enhance the uptake of CH2018 scenario information by stakeholders we here present a newly developed method to create similarity-based storylines and apply it to a historic heatwave event. The resulting storylines show local impacts in four different sectors at individual locations in Switzerland. In each case, the historical record-breaking heat summer of 2003 is related to a future extreme summer represented by the CH2018 scenarios assuming the RCP8.5 emission scenario. Specific indicators help to create unique heat-related storylines. In the alpine setting of Davos, the number of dry hiking weather days increases in a future extreme summer to the delight of hikers and alpine summer tourism. In contrast, the southern cities of Sion and Geneva face less favorable prospects. The fire danger massively increases in dry locations such as Sion. The population in Geneva will encounter an even stronger heat exposure compared to 2003. Finally, the living conditions for a potent agricultural pest considerably improve throughout Switzerland, threatening agriculture during a similar future extreme.

The new similarity-based storylines facilitate the understanding of locally relevant processes linked to climate extremes, provide an improved insight into how extreme events quantitatively change with climate change, give examples of possible impacts, and finally try to stimulate public awareness for possible consequences of future climate change.