What is Vulnerability?

Vulnerability to natural hazards is an integral factor in understanding the true extent of risk. Although there is no single definition for vulnerability, it generally refers to the impact a hazard has on people, infrastructure and the economy. The concept of vulnerability is complex and cannot be comprehensively answered by a single research method. However, aspects of vulnerability to natural hazards can be measured, which is a value adding feature to hazard models, providing a greater understanding of total risk.

Exploring quantitative methods for assessing vulnerability is essential to ongoing risk research, in particular risk decision making, which is a fundamental part of natural hazards risk management. Vulnerability factors can be divided into three main areas; physical, social and economic.

Physical vulnerability

This refers to the potential for physical impact on the built environment or infrastructure and population. This aspect is relatively easily quantified because it depends directly on the physical impact of a hazard event. The best developed vulnerability models have focussed on the behaviour of buildings as the most significant component of the built environment, but in general such models require development and validation using empirical data, post disaster reconnaissance and laboratory testing, such as from shake tables and wind tunnels, as well as computer simulation techniques.

Information can be acquired from countries such as the United States and Europe, but different building techniques, standards and materials adopted in Australia require significant model calibration and testing under Australian conditions. Casualty models have been developed based primarily on assumptions linked to the likelihood of occupants being injured or killed in the event of building damage or failure.

These models draw on the well developed HAZUS risk assessment model used throughout the United States to determine risk from earthquake. The vulnerability of communication lines and other infrastructure has been studied internationally using past disasters as case studies. However, there are limitations on the value of this knowledge being applied to any specific infrastructure systems because it is often the complex network of interactions which dictate the extent of impact and the duration of recovery.

Social vulnerability

Each day, risk managers and risk researchers make decisions about the well being of communities based on available data, anecdotal evidence, training and personal experience. Individuals within communities also make decisions about their own vulnerability to natural disasters and about mitigation and recovery. Approaches to determining social vulnerability rely on the complementary integration of quantitative and qualitative methodologies.

Qualitative approaches have explored the capacity of communities to manage risk information to cope with natural events. Quantitative methods to assess social vulnerability explore the integration of subjective information and analytical processes to develop measures of vulnerability. Such quantitative methods may also be useful when exploring decision making processes concerning socio-economic and community factors. However, as with all vulnerability models, when data from past events is available it should be used to calibrate and validate results.

Economic loss

Broadly, economic loss tends to be classified as tangible and intangible and sub-categorised into direct and indirect loss.

In terms of estimating loss for natural hazards, tangible direct loss is defined as loss resulting from the impact of the event such as physical damage to buildings and their contents, vehicles and infrastructure. Tangible indirect loss relates to the disruption to business, transport, utility networks, clean up costs, emergency response and relief incurred as a consequence of the event.

The extent of the indirect cost is dependent on the availability of alternative sources of supply, markets for products and the duration of any disruption to production. Intangible indirect losses from natural disasters include death, injury and loss of memorabilia. Intangible direct losses incorporate health effects and household disruption to activities such as schooling and social life. There are no market values for intangible losses, but non market valuation techniques can be applied to provide proxy values.

Ideally, an economic assessment of potential or actual losses from a disaster will incorporate all these loss categories. However, in the first instance, tangible loss is likely to be sufficient to provide conservative estimates of economic loss. Intangible loss is more complex to estimate because of the need for proxy values. Direct tangible losses are the simplest to obtain because they follow more directly from the physical impact and are the most readily developed and applied on a regional and national scale.