Compound NaTech risk assessment in dense industrial clusters: Integrating seismic hazards and climate projections using the COHRA-I methodology

Abstract

Natural hazard-triggered technological accidents (NaTech events) pose escalating risks when multiple facilities are simultaneously affected by compound hazards. This study developed the Compound Hazard Risk Assessment for Industries (COHRA-I) methodology, a semi-quantitative risk-screening tool that extends the IPCC AR6 risk conceptualization with four parameters for critical infrastructure interdependencies: Criticality Score (CS), Dependency Factor (DF), Cascade Effect (CE), and Redundancy (RD). Applied to Türkiye's Marmara Region Kocaeli-Gebze industrial corridor (n = 170 upper-tier Seveso III facilities), where industrial clusters concentrate along the North Anatolian Fault Zone (NAFZ), the methodology integrates seismic hazards with climate-driven flood projections (SSP2-4.5 and SSP5-8.5, 2050 horizon). Equipment-specific NaTech multipliers (α = 1.2–1.8 × ), calibrated through eNATECH database analysis (216 events) and Delphi expert elicitation (n = 23, CR = 0.06), account for compound hazard amplification. Results showed that 68% of facilities were within 10 km of the fault trace and 34% fell in combined seismic-flood zones. When NaTech multipliers were applied, 32% of facilities exceeded the critical risk threshold. Climate projections indicate that 7–10 additional percentage points of facilities will transition to critical risk by 2050, with the most rapid escalation occurring in the 2035–2040 window under SSP5-8.5. Spearman rank-correlation analysis identifies Hazard (ρ = 0.72), Cascade Effect (ρ = 0.68), and Vulnerability (ρ = 0.61) as the dominant NaTech risk drivers, with Adaptive Capacity (ρ = −0.58) as the most important protective factor. The methodology was validated against the 1999 Kocaeli earthquake (TÜPRAŞ refinery fires) and the 2023 Kahramanmaraş earthquake sequence (İskenderun Port container fire). COHRA-I is designed as a regional screening tool to prioritize facilities for detailed Quantitative Risk Assessment (QRA), not to replace facility-specific probabilistic safety assessments. A three-tier governance framework (facility–cluster–regional) is proposed for compound hazard management.