A Unified Mathematical Framework for Modelling Multi-Hazard Disaster Risk in the Nigerian Coastal Zone

Nigeria's coastal zone, spanning 853 kilometres of Atlantic coastline across the South West and South South geopolitical zones, is simultaneously exposed to storm surge inundation, land subsidence, erosion, flood events, and oil contamination, yet existing risk assessment tools treat each hazard in isolation, underestimating the compounded risk faced by coastal communities. This dissertation develops a novel unified mathematical framework for multi-hazard risk quantification that captures hazard interdependencies, exposure dynamics, vulnerability functions, and loss estimation within a single probabilistic structure. The framework employs a copula-based joint probability model to characterise the statistical dependence structure among concurrent hazard intensities, overcoming the independence assumptions embedded in existing single-hazard approaches. Vulnerability functions relating hazard intensity to structural and agricultural loss are empirically estimated from household damage survey data covering 1,200 affected properties across five post-disaster events in Bayelsa, Delta, and Lagos coastal communities. A Bayesian hierarchical model propagates parameter uncertainty through the risk calculation chain. Application of the framework to three representative coastal communities yields multi-hazard risk estimates 1.8 to 2.4 times higher than the sum of single-hazard estimates, confirming significant non-additive risk amplification. The framework constitutes an original theoretical and methodological contribution to multi-hazard risk science and provides a replicable tool for coastal adaptation planning in Nigeria and comparable West African settings. Keywords: multi-hazard risk, copula model, Bayesian hierarchical model, Nigerian coastal zone, risk quantification.