Future changes in atmospheric rivers and extreme precipitation in Norway

Abstract

<p>Atmospheric rivers (AR) are associated with flooding events in Norway, like the flood that impacted Flåm in 2014. We assess trends in Norwegian AR characteristics, and the influence of AR variability on extreme precipitation in Norway. After evaluating the global climate model, EC-Earth, compared to the ERA-Interim reanalysis, we show that ARs increase in both intensity and frequency by the end of the century. In two regions on the west coast, the majority of winter precipitation maxima are associated with AR events (> 80% of cases). A non-stationary extreme value analysis indicates that the magnitude of extreme precipitation events in these regions is associated with AR intensity. Indeed, the 1-in-20 year extreme event is 17% larger when the AR-intensity is high, compared to when it is low. Finally, we find that the region mean temperature during winter AR events increases in the future. In the future, when the climate is generally warmer, AR days will tend to make landfall when the temperature is above the freezing point. The partitioning of more precipitation as rain, rather than snow, can have severe impacts on flooding and water resource management in Norway.</p>

The role of spatial and temporal model resolution in a flood event storyline approach in Western Norway

“…2b and c. This is in line with both the facts that the intensity and frequency of ARs reaching the West Coast of Norway are expected to increase in the EC-Earth FUTURE simulations (Whan et al, 2019) and that most extreme precipitation events in the cold season are associated with ARs (Benedict et al, 2019a). It is also in line with the fact that despite the overall response of mean (or median) precipitation in the region being drying for October (see Figs.…”

“…SI Fig. 3 further shows that EC-Earth has a small positive bias in terms of IVT over the North Atlantic Ocean in general compared to ERA-Interim but is generally able to represent ARs statistics properly (Whan et al, 2019). SI Fig.…”

“…Haarsma et al (2013) however provide a more formal evaluation of the model. Whan et al (2019) further found that EC-Earth has a good representation of the annual cycle of AR frequency compared to ERA-Interim (Dee et al, 2011), with most events occurring in September to January. The number of AR events per year in ERA-Interim and EC-Earth is also very similar.…”

“…2 using the ERA-Interim reanalysis in terms of integrated water vapour transport (IVT). ARs are objectively identified by applying a detection algorithm based on the IVT field, as described in Whan et al (2019). The two selected modelled events are shown in SI Fig.…”

“…But even in a region used to heavy precipitation and floods, it is a challenge to decide what (and to what extent) adaptation measures should be considered for the future, when even more precipitation is projected by climate models (Whan et al, 2019). Making sense of and using probabilistic climate projections for extreme weather events is challenging for most decision makers and end-users (Porter and Dessai, 2017).…”