Wflowₛbm v0. 7. 3, a spatially distributed hydrological model: from global data to local applications

Abstract. The wflowₛbm hydrological model, recently released by Deltares, as part of the Wflow. jl (v0. 7. 3) modelling framework, is being used to better understand and potentially address multiple operational and water resource planning challenges from a catchment scale to national scale to continental and global scale. Wflow. jl is a free and open-source distributed hydrological modelling framework written in the Julia programming language. The development of wflowₛbm, the model structure, equations and functionalities are described in detail, including example applications of wflowₛbm. The wflowₛbm model aims to strike a balance between low-resolution, low-complexity and high-resolution, high-complexity hydrological models. Most wflowₛbm parameters are based on physical characteristics or processes, and at the same time wflowₛbm has a runtime performance well suited for large-scale high-resolution model applications. Wflowₛbm models can be set a priori for any catchment with the Python tool HydroMT-Wflow based on globally available datasets and through the use of point-scale (pedo) transfer functions and suitable upscaling rules and generally result in a satisfactory (0. 4 ≥ Kling–Gupta efficiency (KGE) < 0. 7) to good (KGE ≥ 0. 7) performance for discharge a priori (without further tuning). Wflowₛbm includes relevant hydrological processes such as glacier and snow processes, evapotranspiration processes, unsaturated zone dynamics, (shallow) groundwater, and surface flow routing including lakes and reservoirs. Further planned developments include improvements on the computational efficiency and flexibility of the routing scheme, implementation of a water demand and allocation module for water resource modelling, the addition of a deep groundwater concept, and computational efficiency improvements through for example distributed computing and graphics processing unit (GPU) acceleration.