Study regionUpper Nysa Kłodzka River (NKR) catchment, Poland Study focusFloods are one of the most important geohazards, because they can cause negative consequences for human health and life, environment, cultural heritage, economic activity and infrastructure. This study presents a comprehensive assessment methodology of the summer (rainfall-driven) flood hazard applying a probabilistic approach. The research considers interdependencies between flood characteristics (peak flow and flood wave volume) and their relations with the cumulative rainfall recorded before flood events in the upper NKR catchment, one of the most flood-prone areas in Poland. The research is based on daily values of rainfall and river flow for the warm half-year (i.e. from the 1st May to the 31st October) in the multi-annual period 1971–2019. New hydrological insights for the regionThe research allowed to formulate the spatio-temporal rules and dependencies between significant floods characteristics and rainfall, e.g. in terms of the coincidence of flood waves occurrence along the main water course and its tributaries. The research contributes to solving flood management issues in concentric river systems in mountainous areas, such as the upper NKR catchment.