Review article: How hazard-related disruptions become system-wide crises: event-level evidence on failure pathways and continuity functions, 1980&ndash;2025

Bahmani, Homa

doi:10.5194/egusphere-2026-3753

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https://doi.org/10.5194/egusphere-2026-3753

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29 Jul 2026

| 29 Jul 2026

Status: this preprint is open for discussion and under review for Natural Hazards and Earth System Sciences (NHESS).

Review article: How hazard-related disruptions become system-wide crises: event-level evidence on failure pathways and continuity functions, 1980–2025

Homa Bahmani

Abstract. Cascading disasters are increasingly recognized as systemic escalation processes, yet comparative evidence on how initial hazard impacts are transformed into wider crises remains fragmented. Resilience dimensions clarify how system weaknesses interact with triggering hazards and determine whether disruption is absorbed, contained, or transmitted. Drawing on a PRISMA-guided search and targeted supplementary searches, this review synthesizes 43 event-level cascading-disaster cases from 1980 to 2025 to identify failure pathways linking hazards, failure mechanisms, and resilience dimensions. Each event was coded for initiating hazards and transformed hazards, propagation stages, escalation points, failure mechanisms, impacts, and resilience dimensions. Results show that technological and infrastructure failures were the most recurrent transformed hazards, while lifeline failure and secondary hazards formed the main escalation points. Cascade severity depended less on the length of the propagation chain than on which critical functions failed and how disruption propagated through dependent systems. Failure mechanisms clustered around monitoring/control, transport/access, coordination, lifeline services, exposure management, and health-system protection. The resilience crosswalk revealed an interdependence–redundancy gap in which connected systems lacked fallback capacity. These pathways produced persistent recovery burdens. The review proposes a continuity-function framework for cascade-risk reduction, emphasizing monitoring and control, lifeline services, access and logistics, emergency coordination, and equity-sensitive social protection.

Received: 25 Jun 2026 – Discussion started: 29 Jul 2026

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Homa Bahmani

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CC1:
'Comment on egusphere-2026-3753', Ricardo Tavares da Costa, 04 Aug 2026 reply

Please report how M-level assignment was operationalised in practice and how each was placed on the 0–5 scale. This would let readers see whether the scheme actually separates breadth and length or conflates them.

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Citation: https://doi.org/10.5194/egusphere-2026-3753-CC1
- AC1: 'Reply on CC1', Homa Bahmani, 05 Aug 2026 reply
  
  Thank you for this important comment. We agree that the previous Methods section did not explain sufficiently how Alexander’s cascading-disaster magnitude scale was applied in practice. We will therefore clarify the operational definitions of Levels M0–M5 and the event-level classification procedure in the revised manuscript.
  The scale was applied as a qualitative ordinal classification of cascade complexity rather than as an additive numerical score. Following Alexander (2018) and its event-level application by Suppasri et al. (2021), classification was based on three structural components: causes, chains of effects, and escalation points. In our application, initiating and transformed hazards represented the primary and subsequent causes; coded propagation pathways represented chains of effects; and escalation points represented critical junctures at which a hazard, infrastructure failure, or institutional failure generated consequences substantially greater than the initiating impact alone.
  The levels were operationalised as follows: M0 represented one simple cause and effect; M1 one cause and one chain of effects; M2 one cause and two or more chains of effects; M3 two causes, multiple chains of effects, and one significant escalation point; M4 two causes, multiple chains of effects, and at least two significant escalation points; and M5 multiple interacting causes, multiple chains of effects, and multiple escalation points producing exceptionally extensive systemic consequences.
  Each event was reconstructed from the available evidence and matched to the level that best represented its complete cause–effect–escalation configuration. The classification was initially provisional and was reconsidered after targeted supplementary searches when the cascade sequence, escalation points, or downstream consequences remained uncertain. Information not reported in the evidence was not inferred, and evidence completeness was assessed separately from cascade magnitude.
  We also agree that the scale does not provide independent numerical measures of propagation breadth and length. Sequential development is represented through chains of effects, while branching, cross-system spread, and the activation of additional failure pathways are represented through multiple chains and escalation points. These characteristics are therefore integrated within the final qualitative M-level rather than quantified as separate dimensions.
  To examine whether the classification was functioning mainly as a measure of chain length, we separately counted the number of causally supported propagation steps. M4–M5 cases had a higher mean number of steps than M3 cases, but the difference was not statistically significant (7.57 versus 6.47; H = 2.53, p = 0.112). This supports the interpretation that higher M levels were not assigned solely because an event contained a longer sequence of effects.
  The Methods section will be revised as follows:
  After coding the primary source pool identified through PRISMA, each event was assigned a provisional cascade magnitude using Alexander’s cascading-disaster scale (Alexander, 2018), operationalized following its event-level application by Suppasri et al. (2021). The scale was applied as a qualitative ordinal classification of cascade complexity rather than as an additive numerical score. It distinguishes events according to the configuration of causes, chains of effects, and escalation points. In this study, initiating and transformed hazards were treated as primary and subsequent causes, coded propagation pathways represented chains of effects, and escalation points represented critical junctures at which a hazard, system failure, or institutional failure produced consequences substantially greater than the initiating impact alone.
  The levels were interpreted as follows: M0 represented one direct cause and effect; M1 one cause and one chain of effects; M2 one cause and two or more chains of effects without a clearly established escalation point; M3 multiple causes or transformed hazards, multiple chains of effects, and one significant escalation point; M4 multiple chains of effects and at least two significant escalation points; and M5 multiple interacting causes, multiple chains, and multiple escalation points producing exceptionally extensive systemic consequences. Each event was matched to the level that best represented its complete cause–effect–escalation configuration. Borderline classifications were revisited after targeted supplementary searches, and information not reported in the evidence was not inferred.
  The scale does not provide separate numerical measures of propagation breadth and length. Sequential propagation is reflected in chains of effects, while branching, cross-system spread, and the activation of additional failure pathways are reflected in multiple chains and escalation points. Consequently, the M level was treated as a holistic measure of cascade complexity rather than as a measure of chain length alone. Propagation depth was therefore assessed separately through the number of causally supported propagation steps. Cases classified as M3 were treated as moderate cascades, while M4 and M5 cases were combined as high-complexity cascades for group-level analysis; the exact event-level classifications were retained in the database. Cases classified as M0–M2 were excluded because they did not exhibit sufficient cascade complexity to meet the objectives of this review.
  
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  Citation: https://doi.org/10.5194/egusphere-2026-3753-AC1

Homa Bahmani

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Short summary

This review shows how hazard impacts can escalate into broader crises when connected services fail. Across 43 real cases, failures in transport, power, water, health care, warning, and emergency response often allowed disruption to spread and recovery to become prolonged. The study argues that disaster planning should protect the basic functions that keep people safe and essential services working.


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