A concentration of correlated exposures liable to produce simultaneous losses from a single event.
Accumulation, or aggregation, refers to the concentration of exposures within a portfolio that can be hit simultaneously by a single event, turning a multitude of supposedly independent risks into one large-scale loss. Historically central to natural catastrophes, where a single hurricane strikes thousands of policies in the same area, the concept has become decisive in cyber. The key difference lies in the nature of the dependencies: physical accumulation is geographical and therefore visible, whereas cyber accumulation is logical, invisible and unbounded by distance, since it follows shared digital dependency chains. Controlling aggregation is a solvency requirement, because an insurer that ignores its correlations underestimates the maximum possible loss of its portfolio and reserves insufficiently. Management tools include the mapping of common providers, deterministic scenario modeling, sub-limits, exclusions and transfer to reinsurance. The main limitation stems from the youth of cyber data, which makes the calibration of accumulation scenarios far more uncertain than for natural perils that benefit from long historical series.
An insurer discovers that 40 percent of its cyber insureds rely on the same cloud email provider; a prolonged outage of that single vendor would trigger simultaneous business-interruption losses, concentrating the risk on one point.
cumul, accumulation, risque de cumul, aggregation risk