Monthly and daily variations of continental water storage and river discharge were calculated on a global scale with the WaterGAP Global Hydrological ModelGlobal Hydrological Model . In order to improve model results, two major enhancements were added to the model structure. First, a dynamic flow velocitydynamic flow velocity approach was introduced to replace the standard version of a globally constant flow velocity of 1 m/s. Model results were compared to GRACE water storage variationswater storage variations and observed river dischargeriver discharge . The success of the dynamic velocity approach varied among basins and depended on the chosen value for the river roughness parameter. Second, a new reservoir operationreservoir operation algorithm was applied for 487 reservoirs worldwide with a total storage capacity of approximately 4,000 km3. Simulation of reservoir storage changes (but not of basin-wide total water storage variations) and of river discharge was significantly improved. Two different approaches for model calibrationcalibration are combined to obtain a best global-scale estimate of continental water storages and flows.