Trends in Compound Flooding in Northwestern Europe

This study investigates the temporal evolution of compound flooding resulting from extreme coastal water levels and peak river discharge in Northwestern Europe. Compound peak discharge associated with 37 stream gauges with at least 70 years of record availability near the North Sea and Baltic Sea coasts are used to investigate long-term trends in flooding between 1901 and 2014. The temporal evolution of compound flood severity is assessed using a newly developed index, Compound Hazard Ratio (CHR) that compares the severity of river flooding associated with extreme coastal water level with the at-site, T-year fluvial flood. We use extreme value theory and upper tail dependence metrics to investigate trends in compound flooding over the past century and to understand the underlying causes. Our findings highlight the need for systematic evaluation of compound flood hazards and associated drivers for impact assessment in densely populated delta areas.