accidre

Accidre is a concept in complex systems theory used to describe the propensity of a system to undergo a sudden transition between stable regimes as a result of the accumulation of small disturbances over time.

The term is a neologism that has emerged in interdisciplinary discussions about critical transitions. Its etymology is informal, drawing on roots related to occurrence and happening, and it is not tied to a single discipline.

Definition and scope: Accidre is typically treated as a dimensionless index that reflects how susceptible a system is to abrupt change given ongoing perturbations. It integrates factors such as perturbation size, rate, and temporal clustering to estimate the probability of crossing a threshold within a specified time horizon.

Measurement and calculation: In practice, accidre can be inferred from time-series data using indicators associated with critical slowing down, such as rising variance and increasing autocorrelation. It can also be informed by the distribution of event sizes, inter-event times, and patterns of perturbation energy. Modeling approaches may include stochastic bifurcation analyses or network-based percolation frameworks.

Applications and examples: Researchers apply accidre to study ecological regime shifts, climate tipping points, infrastructure networks susceptible to cascading failures, and resilience planning for urban systems. It serves as a heuristic for risk assessment and decision support in contexts where small disturbances accumulate toward a major transition.

Limitations and debate: There is no universal definition of accidre, and several variants coexist across disciplines. Estimation often requires substantial longitudinal data and explicit modeling assumptions; results should be interpreted with caution.

See also: tipping point, critical transition, resilience, regime shift, cascading failure.