In this article the impact of climate change on the overflows of sewer systems is assessed. The emphasis is on the overflows of combined sewer systems. The purpose is twofold: first, to obtain a first-order estimate of the impact of climate change on overflows of sewer systems; and second, to obtain insight into the relevant meteorological variables that are important with respect to climate change. A reservoir model is used to assess the impact of climate change on several combinations of storage capacity and pumpovercapacity of the sewer system. A time series of precipitation depth for Lelystad, with time steps of five minutes, is used as a base case for comparison. Two types of scenarios are used to assess the sensitivity for elimate change: artificial climate scenarios and scenarios based on the analogous elimate method.