Increasing risks of extreme salt intrusion events across European estuaries in a warming climate

Over the last decade, many estuaries worldwide have faced increased salt intrusion as a result of human activities and a changing climate. Despite its socio-economic importance, our current projections on the statistics of future salt intrusion are limited to case studies in certain regions. Here, we show that, compared to present-day conditions, river discharge in the summer months is projected to be reduced by 10–60% in 17 out of 22 investigated major European river basins at the end of the 21^st century under the high CO₂ emission scenario (Shared Socioeconomic Pathways, SSP 3-7.0). We find that the reduced future river discharge in the summer months, in turn, increases salt intrusion lengths by 10–30% in 9 representative European estuaries at low and mid latitudes. Our analysis further indicates that the European estuaries are projected to experience more than five times more frequent extreme salt intrusion events.