In Berlin, Germany, the demand for enhanced protection of the environment and the growing economic pressure have led to an increased application of control concepts within the sewage system. A global control strategy to regulate the pumpage of the combined sewage system to the treatment plant was developed and evaluated in a theoretical study. The objective was to reduce CSO. In this paper an extension of the existing control algorithm by information from online rainfall measurement and radar nowcasting is described. The rainfall information is taken into account by two additive terms describing the predicted volume from rainfall runoff. On the basis of numerical simulation the potential of these two complementary forecast terms in the global control algorithm to further reduce CSO is evaluated. The investigations are based on long-time simulations that are conducted with the dynamic flow routing model InfoWorks for three subcatchments of the Berlin drainage system. The results show that at the current Berlin system a CSO reduction of only 0.8% is possible. The effect of the forecast terms is limited by operational constraints. Limits are set to both, the delivery from each individual pump station and the total pumpage to the treatment plant.