This thesis describes how variability in different components of the hydrological cycle (precipitation, runoff generating processes, and evaporation) influences the hydrological response in the Rhine basin. The chapters cover three important steps in hydrological research: understanding past events through analysis of observations, conceptualising hydrology through testing and developing models, and understanding the hydrological response under changing conditions. It is shown that the complex interactions between different components of the hydrological cycle, as well as the contrasting responses to changing climate conditions need to be represented correctly to provide reliable discharge estimates. This thesis gives insight on how to capture the hydrological variability to improve how hydrology can support a safer environment.