Exploring the sensitivity of extreme event attribution of two recent extreme weather events in Sweden using long-running meteorological observations

Abstract. Despite a growing interest in extreme event attribution, attributing individual weather events remains difficult and uncertain. We have explored extreme event attribution by comparing the method for probabilistic extreme event attribution employed at World Weather Attribution (https://www.worldweatherattribution.org, last access: 22 August 2024) (WWA method) to an approach solely using pre-industrial and current observations (PI method), utilising the extensive and long-running network of meteorological observations available in Sweden. With the long observational records, the PI method is used to calculate the change in probability for two recent extreme events in Sweden without relying on the correlation to the global mean surface temperature (GMST). Our results indicate that the two methods generally agree for an event based on daily maximum temperatures. However, the WWA method results in a weaker indication of attribution compared to the PI method, for which 12 out of 15 stations indicate a stronger attribution than found by the WWA method. On the other hand, for a recent extreme precipitation event, the WWA method results in a stronger indication of attribution compared to the PI method. For this event, only 2 out of 10 stations assessed in the PI method exhibited results similar to the WWA method. Based on the results, we conclude that at least one out of every two of heat waves similar to the summer of 2018 can be attributed to climate change. For the extreme precipitation event in Gävle in 2021, the large variations within and between the two methods make it difficult to draw any conclusions regarding the attribution of the event.