Inseparability in Disaster Risk Science: Accounting for Coupled, Co-Evolving Systems

Contemporary risk landscapes are shaped by systemic phenomena-compound disasters, cascading failures, non-stationarity, and cross-domain crises-that challenge conventional frameworks. While the classical risk equation (Risk = Hazard × Vulnerability × Exposure) remains a useful heuristic, it relies on a separability assumption that breaks down in feedback-rich, co-evolving systems. This failure reflects a familiar diagnosis: risk can be mistaken for a complicated problem, decomposable and optimizable, when it is a complex one, characterized by emergence and adaptation. Our contribution herein is not this distinction but its analytical consequence. Drawing on an interdisciplinary workshop on systemic risk and resilience, we propose inseparability as a foundational premise for disaster risk science. Hazard, exposure, and vulnerability might be better understood as dynamically coupled processes rather than separable variables. We derive implications across four axes: reframing vulnerability as a non-ergodic system property; addressing cross-scale dynamics; shifting from risk control to adaptive management; and treating knowledge co-production as a scientific necessity.