Monthly and Daily Variations of Continental Water Storage and Flows

Monthly and daily variations of continental water storage and river discharge were calculated on a global scale with the WaterGAP Global Hydrological Model. In order to improve model results, two major enhancements were added to the model structure. First, a dynamic 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 variations and observed river 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 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 calibration are combined to obtain a best global-scale estimate of continental water storages and flows.