See: Comparative Glossary (Conclusions): Another prerequisite for a disaster besides hazard is vulnerability. Vulnerability is a dynamic, intrinsic feature of any community (or household, region, state, infrastructure or any other element at risk) that comprises a multitude of components. The extent to which it is revealed is determined by the severity of the event. Vulnerability indicates a damage potential and is a forward looking variable. Or as Cannon et al. (2004) characterized it, vulnerability (in contrast to poverty, which is a measure of current status,) should involve a predictive quality: it is supposedly a way of conceptualizing what may happen to an identifiable population under conditions of particular risk and hazards. Determining vulnerability means asking what would happen if certain event(s) impacted particular elements at risk (e.g. a community). Vulnerability is an intrinsic characteristic of a community that is always there even in quiescent times between events. It is not switched on and off with the coming and going of events; rather, it is a permanent and dynamic feature that is revealed during an event to an extent that depends on the magnitude of the harmful event. This means that vulnerability can often only be measured indirectly and retrospectively, and the dimension normally used for this indirect measure is damage or more general harm. What is normally seen in the aftermath of a disaster is not the vulnerability per se, but the harm done. Seeing the damage pattern of a community without knowing the magnitude of the event does not allow conclusions regarding the community's vulnerability. In that sense the magnitude-damage relationship reflects the vulnerability of an element at risk (community, household, nation, infrastructure etc.). Figure 2. Sample residential damage function for the hazard of tornado illustrates the progression of wind damage. Source: Doggett (2003). Tornado intensities are marked from F0 to F5 on the Fujita Scale. The full relationship between windspeed and damage characterizes the physical vulnerability of a certain building type. Vulnerability changes continuously over time and is usually even affected by the harmful event itself. It can increase, for example, if poverty has been heightened by a disaster, so that the next disaster will have an even more devastating effect on the impoverished community. A small event, however, can raise the awareness of the community and in that way decrease its vulnerability. Vulnerability is a function of the sensitivity or susceptibility of a system (community, household, building, infrastructure, nation etc.). It is independent from any particular magnitude from a specific natural event but dependent on the context in which it occurs. Vulnerability cannot be assessed in absolute terms; the performance of the urban place should be assessed with reference to specific spatial and temporal scales (Rashed and Weeks, 2002). For practical reasons a vulnerability analysis will often limit itself to a certain scenario, i.e. event magnitude, for which an analysis is carried out. This is usually an appropriate approach to assessing vulnerability, but the choice of the event scenario is a subjective one. What scenario should be chosen: The 100 year event, 200 year event, the largest event that has occurred in the living memory, or the 5 m flood level? In earthquake engineering this susceptibility is often quantified by means of a damage ratiothat can vary between no damage (0%) and total destruction (100%). But vulnerability has many dimensions physical (built environment), social, economic, environmental, institutional, and human and many of them are not easily quantifiable. The complexity of vulnerability is not only given by its multiple dimensions but also by the fact that it is site-specific and that its parameters change with geographic scale. The parameters that determine vulnerability are different on the household-, community-, and country-level. In the economic dimension of the household-level, parameters such as the amount and diversity of income of single persons are relevant, whereas on a country-level, inflation rate and GDP are more appropriate. The limitations of vulnerability theory in addressing complex and dynamic reality are noted in Duryog Nivaran's book: Understanding Vulnerability. He says that vulnerability is too complicated to be captured by models and frameworks. There are so many dimensions to it: economic, demographic, political, and psychological. There are so many factors making people vulnerable: not just a range of immediate causes but if one analyses the subject fully a host of root causes too investigations of vulnerability are investigations into the workings of human society, and human societies are complex so complex and diverse that they easily break out of any attempts to confine them within the neatly drawn frameworks, categories, and definitions. They are also dynamic, in a state of constant change, and, because they are complex and diverse, all the elements within societies are moving, so that these changes occur in different parts of society, in different ways and at different times (Twigg, 1998). On a more optimistic note, every vulnerability analysis requires adaptation to its specific objectives and scales. Professionals in that field must be aware that there are many answers to the question of vulnerability. One potential answer to the question of vulnerability is given in Birkmann (2006), who defines vulnerability in a more encompassing way so that it includes exposure and coping capacities of a community