Extreme rainfall events in southern Sweden: where does the moisture come from?

Abstract

The atmospheric transport of moisture leading to extreme summer precipitation events in southern Sweden was investigated using a Lagrangian trajectory model. Surprisingly, we found that the trajectories crossed continental Europe and the Baltic Sea before arriving over Sweden; they did not arrive directly from the North Sea. Such transport pathways were not seen for a control sample of non-extreme rainfall events. We then used a new source region identification technique to investigate the hypothesis that Europe and the Baltic are important sources of the moisture that is rained out in the extreme events. Although the results varied between events, we found that this is indeed the case. Our results establish the atmospheric transport patterns that are apparently a pre-requisite for extreme rainfall events to occur in southern Sweden, and further suggest regional moisture availability may also play a key role.