Long-term coastal management of beach/dune systems requires the definition and assessment of storm events. This study presents a framework using statistical analyses and numerical modelling (XBeach) to characterize storm events and investigate their impact on beach/dune erosion. The method is developed using exemplary data from Formby Point on the Sefton coast (UK), which has a complex beach morphology and frontal dunes. Relevant storm events are classified by a versatile univariate response function taking into account both nearshore water levels and offshore significant wave heights (Hs). It is shown that compared to the established storm classification (Hs ≥ 2.5 m) 35% more storm events that are relevant for beach/dune erosion are identified. Also the events exceed critical conditions for longer durations, and cause greater erosion impact (12%) along the beach/dune profile. The proposed classification of storm events thus captures relevant events for the storm erosion and can inform coastal management strategies. This framework is widely applicable to other beach/dune systems. © 2021 The Authors