Development and validation of a coupled simulation framework representing the hydro- and thermodynamics in rivers and lakes (TCHOIR)

Natural and artificial lakes are one of the critical water resources for anthropogenic activities and environmental flows. Riverine in- and outflows are also dominant on the water budget in addition to vertical fluxes containing precipitation and evaporation. However, much previous research has been done on developing in-lake models ignoring the connectivity with up and downstream areas, mainly to assess water quality and provide lower boundary conditions for atmospheric models. Here we propose a coupled simulation framework of river and lake models representing hydro- and thermodynamics, Tightly Coupled framework for Hydrology of Open water Interactions in Riverlake network (TCHOIR). It provides a global-scale grid system allocating rivers and lakes upscaled by high-resolution topography and lake datasets and a coupler to exchange the up- and downstream boundary conditions for each model. TCHOIR is validated on a global scale for river discharge, river water temperature, lake surface elevation, and lake surface temperature with in-situ observation data and satellite-based products. The results indicate that coupling the models to represent the interactions between rivers and lakes improves the reproducibility compared with the uncoupled model. In particular, TCHOIR is an unprecedented model to reproduce the absolute value and seasonal variability of the lake surface elevation. Further studies are expected to implement a dam operation model to the lake outlets to evaluate the anthropogenic impacts on the water resource amount and water quality in the downstream area.