The co-incidence of storm surges and extreme discharges within the Rhine–Meuse Delta

Authors: W J Klerk and Hessel C Winsemius and W J van Verseveld and A M R Bakker and F L M Diermanse
Journal: Environmental Research Letters
Year: 2015

The Netherlands is a low-lying coastal area and therefore threatened by both extreme river$backslash$r discharges from the Meuse and Rhine rivers and storm surges along the North Sea coastline. To date,$backslash$r in most flood risk analyses these two hazardous phenomena are considered independent. However, if$backslash$r there were a dependence between high sea water levels and extreme discharges this might result in$backslash$r higher design water levels, which might consequently have implications for flood protection policy$backslash$r in the Netherlands. In this study we explore the relation between high sea water levels at Hoek van$backslash$r Holland and high river discharges at Lobith. Different from previous studies, we use physical models$backslash$r forced by the same atmospheric forcing leading to concomitant and consistent time series of storm$backslash$r surge conditions and river discharge. These time series were generated for present day conditions as$backslash$r well as future climate projections and analysed for dependence within the upper tails of their$backslash$r distribution. In this study, dependence between the discharge at Lobith and storm surge at Hoek van$backslash$r Holland was found, and the dependence was highest for a lag of six days between the two processes.$backslash$r As no significant dependence of the threats was found for cases without time lag, there is no need$backslash$r for considering dependence in flood protection and policy making. Although future climate change is$backslash$r expected to lead to more extreme conditions in river discharges, we cannot conclude from this study$backslash$r that it will change the magnitude of the dependence for extreme conditions.