Supply-demand mismatch causes substantial deterioration in prehospital emergency medical service under disasters.

Floods severely disrupt prehospital emergency medical services (EMS), which dispatch medical personnel to deliver on-scene treatment, by hindering ambulance mobility and increasing medical demand. Here, we proposes a simulation-based framework that integrates flood inundation, EMS facility data, and population-weighted medical demand to assess regional EMS performance under different flood scenarios. Applied to Zhengzhou, China, the framework evaluates system responses during normal conditions, 1-in-50-year, 1-in-100-year floods, and the extreme "7.20" rainfall disaster. Results show dramatic increases in response times during "7.20", with resource shortages identified as a key delay factor. Three mitigation strategies are evaluated: adding ambulances, inter-subcenter ambulance sharing, and a hybrid approach. The results demonstrate that ambulance sharing outperforms limited ambulance additions, increasing 10-min and 30-min population coverage by 15.2% and 22.7%, respectively, while the hybrid approach achieves optimal improvement. The findings offer policy guidance for improving EMS resilience in flood-prone regions and support global urban disaster preparedness.