Coupling a large-scale hydrological model to a high-resolution hydrodynamical model: A study of floods within the Niger Inner Delta as a first step towards a potential global application

Abstract

Floods are one of the most frequently occurring natural disasters with severe impacts on a global level. This has led to an increased attention for global flood risk assessments, which require global hydrological models to make an analysis of future scenarios possible. However, global models operate on scales much larger than those required to accurately model floods. Downscaling techniques have been used to fix this issue, but these cannot account for dynamic feedback effects to hydrological processes. Therefore, a new approach has been investigated in which a global hydrological model (PCR-GLOBWB) is coupled to a high-resolution hydrodynamical model (D-Flow Flexible Mesh) that operates on the fine scales required for flood modelling and allows the inclusion of dynamic feedback effects. An automated grid creation procedure, based on the Height Above Nearest Drainage (HAND) algorithm, is used for the hydrodynamical model to ensure that the coupled setup could be applied on a global scale. The coupling between models is facilitated with the Basic Modeling Interface (BMI). Several coupled model setups are tested for the Niger River and its Inner Delta; a large seasonality inundated wetland where floods are known to have a large impact on hydrological processes. Results indicate an improvement over the stand-alone models and identify remaining issues which will need to be dealt with before the coupled model can be applied on a global scale.