Climate change will affect flood regimes in many areas of the globe. Given that flooding is among the most significant natural disasters, estimating future flood risk is important for considering mitigation and adaptation strategies to climate change. However, future climate projections still have large uncertainties due to differences among global climate models (GCMs), different methods for correcting GCM biases, and different potential emission scenarios. Future flood risk assessment requires large-ensemble flood simulations to account for these uncertainties. In this chapter, we provide a review of global river model development, including the introduction of a highly advanced CaMa-Flood model, which has both the high computational efficiency and high simulation accuracy required for global ensemble simulations. We assessed future flood risk at a global scale using CaMa-Flood and runoff output from CMIP5 GCMs. The simulation results suggest that flood risk is generally increased on a global scale by global warming, although some regions show a decrease in flood risk. More important, some areas show different trends in future flood risk if different GCMs are used, which suggests the importance of multimodel ensemble simulations for flood risk assessment under climate change conditions.