Systemic resilience of megacities against respiratory epidemics: A multi-scale coupled framework

Megacities exhibit pronounced systemic vulnerability to respiratory epidemic shocks due to their complex and heterogeneous social contact structures. Characterizing how epidemic shocks spread through such systems and how interventions reshape systemic resilience remains a critical challenge in system safety and reliability engineering. We propose a multi-scale coupled dynamic framework to quantitatively assess the resilience performance of megacities under epidemic shocks. The results reveal that megacity resilience is not a homogeneous system property but an emergent outcome shaped by the underlying complex social network structure. Population scale drives a mass effect in middle-aged groups, whereas localized high-frequency contacts among younger cohorts lead to cohort saturation. High contact diversity breaks age-based protective barriers through a bridging effect, rendering households major spreading hubs, while age-homophilic contact patterns create age-island effects that confer local saturation-based resilience advantage to schools. Counterintuitively, individual-level protective behaviors may trigger discontinuous resilience phase transitions, exposing the system to abrupt collapse risks, whereas risk perception-driven interventions can generate non-monotonic resilience recovery. The systemic robustness of epidemic spreading networks constrains localized interventions targeting single venues, potentially causing risk migration and load redistribution. Cross-domain synergistic intervention strategies leverage nonlinear synergistic effects to dismantle this robustness, achieving fast and mild risk clearing as well as resilience optimization.