Recent changes in circulation patterns and their opposing impact on extreme precipitation at the west coast of Norway

Abstract

Understanding recent and future changes of extreme precipitation is essential for climate change adaptation. Here, we use 3800 extreme precipitation events produced by an ensemble seasonal prediction system. The ensemble represents the climate from 1981 to 2018 and we analyse 3-day maximum precipitation events in September–October–November for the west coast of Norway. Two dominant atmospheric patterns, described by an empirical orthogonal function (EOF) analysis, are related to the results of the extreme value statistics. The principal components of the second and third mode of EOFs have significant trends over the last 40 years, but with an opposing impact on the return values of extreme precipitation. This explains the observed stationarity of extreme precipitation over recent decades at the west coast of Norway, which was also found in previous studies. The second mode of EOFs also shows a relation to the sea-ice coverage in the Barents and Kara Seas, which suggests a connection between the decline of sea-ice to the changes in the atmospheric pattern.

Keywords

• Extreme precipitation
• Circulation patterns
• Ensemble data set
• Trends