The rise of short-duration extreme rainfall events across Central Europe has exposed critical weaknesses in traditional flood risk management methods that depend on fixed return periods and design thresholds. In response, this paper introduces FLOOD-ST: a scenario-based operational stress testing framework designed to evaluate the functional limits and vulnerabilities of water infrastructure systems under realistic, high-impact flood scenarios.</p> <p>FLOOD-ST combines synthetic rainfall archetypes, varying antecedent soil moisture conditions and infrastructure-specific scenarios to systematically evaluate system performance. By integrating elements of functional stress testing, the framework diagnoses weak points and illuminates cascading failure pathways across interconnected assets. Unlike traditional hazard mapping, FLOOD-ST does not aim to replace existing tools but complements them by offering a diagnostic view of system behaviour during extreme conditions. The framework is platform-independent, modular, and scalable, making it suitable for both urban and rural catchments, especially those characterised by high system complexity, short warning times, or critical interdependencies.</p> <p>This paper describes the conceptual foundation, simulation workflow, and real-world applications of FLOOD-ST, demonstrating its potential to support adaptive planning, emergency preparedness, and climate-resilient water management.