See: Comparative Glossary (Conclusions): Every disaster starts with a hazard – known or unknown. There are many ways to characterize hazards, e.g. natural, technical, man-made, nuclear, ecological. The categories are probably as diverse as the disciplines and sectors involved. But they all have in common the potential to cause the severe adverse effects that lie at the bottom of every emergency, disaster, and catastrophe. A hazard can be as general as “flood” or “storm” and, as such, stand for groups of potentially harmful events of variable severity. In other words, the hazard “storm” refers to all potential wind speeds that can be expected in a given region. A hazard can also be formulated more specifically as a magnitude 7.2 earthquake in Los Angeles or a category 5 Hurricane hitting the Philippines. In that case we are dealing with a specific hazard scenario. One important feature of hazard is that it has the notion of probability, or a likelihood of occurring. A hazard is a threat, not the actual event. Any hazard can manifest itself in an actual harmful event. In other words, if it can be measured in terms of real damage or harm it is no longer a hazard but has become an event, disaster or catastrophe. Every specific hazard magnitude is attached to a usually empirically derived return period, which is site-specific. The return period of a category 5 hurricane is different for New Orleans compared to the Philippines. If hazard is pegged out more broadly such as “epidemic”, “drought” or “flood”, it is characterized by all possible magnitudes. In order to quantify hazard, each magnitude is tied to a specific return period or its inverse, frequency. The latter ensemble is the magnitude-frequency relationship of a particular hazard and it is always an inherent characteristic of a specific locality or region. Figure 1. For earthquake hazard, the two lines represent the different magnitude-frequency relationships for two different fictitious regions, region x and region y. The two lines are region-specific.