Modeling the Nile: A Comprehensive Water Budget and Flow Assessment with the River Basin Flow Model (RBFM)

The Nile River basin, covering 2.9 million km³ across 11countries, is one of the world's most complex hydrological systems. With an annual historical discharge of 84 billion m³ at Aswan, Egypt, and rainfall of around 1,660 billion m³ per year over the Nile basin, effective management of this vital transboundary resource requires a deep understanding of its hydrology. This study offers a comprehensive description of the Nile’s hydrology and presents a detailed review of the existing flow models applied to the basin. To advance this understanding, the study introduces a new water budget model, the River Basin Flow Model (RBFM), designed to simulate water dynamics across the entire Nile River basin. The RBFM divides the basin into interconnected units, where each unit is characterized by variables such as rainfall, evaporation, seepage, area, water depth, bed elevation, slope, and the number of connected catchments. For each connected catchment, the model incorporates factors such as area, rainfall, losses, and runoff coefficients. By simulating the water budget for each unit, the model calculates the resulting outflow. Although currently run on an annual basis due to data constraints, the model is capable of simulating monthly or finer temporal steps. The RBFM closely matches historical data, replicating the Nile's long-term average discharge: 24.1 billion m³ from the White Nile, 49.6 billion m³ from the Blue Nile, and 84.1 billion m³ at Lake Nasser, aligning with observed values from 1910-1995. The model also examines the impacts of changes in land cover, rainfall, and land use on the basin's water yield. It demonstrates that the Blue Nile is more sensitive to such changes compared to the White Nile, offering valuable insights into how environmental and anthropogenic factors affect the river's flow. This study underscores the RBFM's value as a simple yet effective tool for assessing the impacts of climate change, land use modifications, and dam construction on the Nile's water resources. Its minimal data requirements make it adaptable for application in other river basins globally. The model offers a practical approach for sustainable water management and policy development, supporting informed decision-making for one of the world’s most critical river systems.