C-CWatM v1.0: A high-resolution water resources and river routing model enabling direct linkage to state-of-the-art Earth-system and land‑surface models

Abstract. River routing and human water management are often poorly represented in many Earth-system and land-surface models, not permitting consistent assessments of human-water-climate interactions. In this work, we introduce C-CWatM v1.0 (Climate-CWatM v1.0), a land-surface-driven version of the Community Water model (CWatM) that enables online and offline simulations of river routing, water resource availability, and management. The model operates on standard land-surface output and includes an OASIS3-MCT coupling interface, enabling efficient two-way coupling with Earth-system and land-surface models. In comparison to CWatM, all modules related to land-surface and snow processes have been removed to prevent conflicts with land-surface parameterisations implemented in the coupled models. C-CWatM also offers options for reducing-forcing requirements and simple on-the-fly bias correction using predefined quantile weights. We test C-CWatM in both online and offline settings and evaluate the model performance in offline mode using REMO output across a European domain. C-CWatM reproduces large-scale discharge patterns and hydrological gradients when using non-bias-corrected forcing data without calibration of model parameters. Calibration results in moderate improvements in model performance, while quantile-mapping-based bias correction of runoff significantly enhances model skill. A reduced-forcing version of the model enables rapid simulations based on available climate model output, as demonstrated using readily available EURO-CORDEX output. C-CWatM provides a novel and flexible hydrological and water resources modelling tool for representing river routing and water management in coupled modelling systems, enabling more integrated analyses of climate-water-human interactions.