A Northern European paradox: both wetting and drying trends complicate water management

The diverging trends in annual soil moisture across Europe are stark: Northern regions are increasingly wet, while Southern areas face growing aridity, largely due to contrasting precipitation patterns between these regions. While several studies have examined the consequences of soil moisture deficits and drought in the south, the implications of increasing soil moisture levels in the north remain less explored. This study leverages reanalysis products, such as ERA5-Land, to delve into the soil moisture dynamics of Northern Europe, examining seasonal and sub-seasonal trends across the period 1951-2020. This research includes both a detailed case study of Denmark, and an analysis focusing on the Northern European domain. A primary hypothesis is that spatiotemporal soil moisture trends are influenced not only by changes in mean precipitation, but also by altered temporal patterns of rainfall at sub-seasonal scales across the domain. Moreover, increased soil moisture persistence during the wet season heightens the risk of complex and compound hydro-meteorological interactions between saturated soils and intense rainfall events. The analysis also uncovers a north-to-south soil moisture gradient within Northern Europe, particularly evident with spring drying (MAM). In the southern parts of Northern Europe (including Denmark, southern Sweden, and the Baltic region) this manifests as a wetting trend in winter (DJF) and a drying trend in spring (MAM), posing challenges for water management across sectors. The findings of this study underscore critical research areas requiring further investigation, such as the impacts of increasing soil moisture and more frequent intense rainfall events on streamflow and flooding. Future research could benefit from employing hydrological models to explore these dynamics in greater detail.