Introducing WSFS-P, Process-based Version of the Watershed Simulation and Forecasting System (WSFS) in Finland

This study introduces the WSFS-P model, an evolution of the well-established national WSFS (Watershed Simulation and Forecasting System) hydrological model. This new model represents a significant shift, moving from a conceptual WSFS hydrological model framework to a more physically based, and process-oriented approach (WSFS-P). WSFS-P is a two-layer semi-distributed hydrological model developed at the Finnish Environment Institute (Syke) in order to offer more detailed physical representations in hydrological forecasting and research. This hydrological model incorporates a number of sub-models that cover a wide range of hydrologic processes, including precipitation, snow dynamics, evapotranspiration, lake evaporation, soil moisture, groundwater, river routing, and ice thickness. The model utilizes meteorological inputs such as precipitation, temperature, relative humidity, air pressure, net radiation, cloudiness, and wind speed to deliver a comprehensive and detailed simulation of the hydrological cycle. The WSFS-P aims to enhance the accuracy and effectiveness of hydrological forecasting and research in Finland by leveraging spatially distributed data, such as Corine land use, altitude, and Finnish soil database. This model covers the entire Finnish mainland and transboundary catchments but excludes islands and smaller coastal catchments. This study assesses the WSFS-P model in 58 different catchments in Finland that were selected to cover diverse hydrological characteristics, reliable data, and minimal influence from lake regulation. The selected catchments feature a variety of catchment sizes and topographical and land-use patterns, including forests and agricultural areas, and have varying soil types and distinct climatic conditions. Several catchments are characterized by numerous lakes typical to Finland. Additionally, the study provided a comprehensive examination of five specific catchments to highlight the model’s effectiveness. The preliminary results demonstrate the model’s capabilities in predicting water availability, contributing to efficient water resource management and enhanced flood and drought prediction in Finland. This study aims not only to introduce the WSFS-P model but also to validate its operational readiness for diverse hydrological conditions.