Changes in the Earth’s climate system do have consequences for the river discharges. The development of the future climate is uncertain, which causes uncertainty in the future extreme river discharges. For flood protection considerations, it is important to quantify the climate uncertainties and its effects on extreme river discharges. In this study the uncertainty in extreme river discharges due to Climate Change is quantified. The results indicate the uncertainty in discharge return levels given a specific forcing scenario. Subsequently, the discharge return levels of the KNMI climate scenarios are compared with the found results for the forcing scenarios. The study also provides the consequences of the uncertainty in discharge return levels on the design water levels. The results give the uncertainty in the design water level and the additional height in design water level required to take account for this uncertainty.