Following the "probability-consequence" framework, risk index methods provide an alternative way of QRA . A risk index is a comprehensive, integrated representation of accident frequency and consequence. To evaluate the risk associated with crosscategory hazards coupling scenarios, Marzo et al. developed a short-cut methodology for assessing the vulnerability of territory around an industrial plant. The combined use of a global key hazard indicator with the key vulnerability indicator allowed the measurement of the risk arising from the presence of a plant in a territory with given characteristics. Zhang et al. developed a GIS-based spatial multi-index model for large basin-scale flood risk assessment. The flood risk was classified into indexes of hazard, vulnerability, and exposure. However, risk index methods hardly provide a uniform criterion for risk assessment . The risk values may span over a risk level among different preferred indicators for the same scenario .