Biogeomorphic modeling: how to account for subgrid-scale interactions between hydrodynamics and vegetation patches

Interactions between water flow and patchy vegetation are governing the functioning of many ecosystems, such as river beds, floodplains, wetlands, salt marshes, mangroves and seagrass meadows. However, numerical models that simulate those interactions explicitly, including at the patch-scale (that is, at resolutions below a m²), together with their far-reaching geomorphological and ecological consequences at the landscape-scale (that is, for domain sizes of several km²), are still very computationally demanding. In this communication, we will present a novel efficient technique to incorporate biogeomorphic feedbacks across multiple spatial scales (from below a m² to several km²) in biogeomorphic models. Our new methodology is based on the mathematical concept of convolution, allowing to spatially refine coarse-resolution (order of meters) hydrodynamic simulations of flow velocity fields around fine-resolution (order of dm) patchy vegetation patterns. We will demonstrate the power of our new method, by comparing our results with reference fine-resolution (order of cm) hydrodynamic model runs, which themselves are calibrated against flume measurements. We will show that our new model approach enables to refine a coarser-resolution hydrodynamic model, by resolving subgrid-scale fine-resolution flow velocity patterns within and around patchy vegetation distributions. With simple example cases, we will show evidence that our novel approach can substantially improve the representation of important processes in current biogeomorphic models, such as subgrid-scale effects on sediment transport and vegetation growth. Finally, we will demonstrate that our convolution method is an important step forward towards more computationally efficient multiscale biogeomorphic modeling, as compared with what is possible to date.