Introduction

A disaster is any event that leads to human, material, economic and environmental losses, and impacts, as a consequence of the interaction between the said event and the conditions of exposure and capacity, upsetting the daily functioning of society1. These disasters can vary in range from natural disasters, slow or rapid onset events caused by natural processes such as earthquakes floods and storms, to technological disasters, which are mainly caused by humans such as gas leaks or explosions etc2,3.

The UN secretary general, Kofi Annan wrote in 199911 stressed that these disasters always depend on the interaction between nature and society’s vulnerability. Vulnerability can to some extent be controlled, and in some cases human actions may increase the risk of extreme natural events e.g. deforestation leading to faster run-off and increased flood risk, and the impact of anthropogenic emissions on climate. Thus, the use of the term “natural” may be misleading as it may imply that the disaster is largely beyond human control. That the majority of disaster victims are in developing countries indicates the importance of vulnerability. This can be particularly seen in the Asia-Pacific region, as it is one of the most affected, and the most populated, regions in the world, seeing 55 earthquakes, 217 storms and cyclones, and 236 cases of severe flooding, impacting 650 million people and 33,000 fatalities between 2014 and 2017 alone12.

One way to look at disasters is to look at disaster risk, which is defined by the UNISDR as “The potential loss of life, injury, or destroyed or damaged assets which could occur to a system, society or a community in a specific period of time, determined probabilistically as a function of hazard, exposure, vulnerability and capacity’’4. This risk depends on the interaction between hazards and the socio-economic characteristics that make people and places vulnerable and exposed. The risk can be expressed as the likelihood of loss of life, injury or destruction and damage from a disaster in a time-period5. Socio-economic risk drivers, such as poverty, inequality, rural and urban development etc influence the vulnerability and exposure to hazards and understanding disaster risk requires us to not only consider the hazard, our exposure and vulnerability but also society's capacity to protect itself from disasters.

It is in the best interest of society to accurately identify, assess and quantify disaster risk to facilitate its reduction. Comprehensive risk assessment depends on information such as historical disaster events and their driving processes, potential disasters in the future and other factors such as effects of urbanisation and climate change. The major components risk assessment includes the probability of experiencing a certain intensity of hazard at a given location based on historical data, property and infrastructure exposed to a hazard inclusive of socioeconomic factors and the susceptibility to damage of the assets exposed to the forces generated by the hazard7. Investing in disaster risk reduction is one of the best ways to reduce potential losses from a disaster. It is a people-centred approach that relies on the contribution of public and private sectors to build the resilience of society to multiple hazards and instilling values of prevention and safety amongst the people.

Human actions may increase risk to humans, e.g. socio-economic pressures encouraging people to live in high disaster risk regions, such as on flood plains, in zones with a high seismic hazard and on unstable hill slopes; or may decrease risk e.g. via earthquake resistant buildings. Effective hazard assessment and mitigation techniques can significantly reduce risk. For example, actions in China led to a radical reduction in fatalities from floods, from several million in 1931 to a few thousand in 19983.

Hazard is one of the components of risk assessment and disaster events are only called hazards if they have the potential to cause harm to humans or the environment or cause socio-economic losses. The location of these events is linked to locally occurring natural processes, such as plate tectonics, weather and climate etc. However, anthropogenic activities, such as urbanization, environmental degradation etc, can also determine whether the natural hazard can manifest into a disaster and, also, affect the intensity and frequency of occurrence of the disaster5. Hazards can be classified into different categories such as biological hazards, environmental hazards, geological or geophysical hazards, hydrometeorological hazards and technological hazards. Each category can be further divided into subcategories and can also trigger secondary hazards themselves leading to a cascading effect. Hazard assessment involves identifying the source of hazard(s) at a given location and collating relevant hazard-related data, most importantly the date of occurrence, the origin and extent of the area of effect, and the maximum observed intensity based on historical data. Although the negative impacts cannot be fully avoided, it is possible to reduce their scale or intensity through different strategies, such as cataloguing and collating hazard data to better inform early warning systems, which are tied to several disaster risk reduction strategies5.

Exposure is another component that is a part of disaster risk assessment. It is defined as “The situation of people, infrastructure, housing, production capacities and other tangible human assets located in hazard-prone areas4”. Measures of exposure can include the number of people or types of assets in an area. This is an important component as it is directly proportional to the disaster risk. With economic exposure trending upward in high hazard areas5, it is crucial to reduce exposure in these areas. Techniques such as land use planning and planned evacuation aided by early warning systems can be helpful when exposure cannot be avoided.

Vulnerability is another important component of risk assessment and is defined as “The conditions determined by physical, social, economic and environmental factors or processes which increase the susceptibility of an individual, a community, assets or systems to the impacts of hazards”4.  Vulnerability can be described in many dimensions: namely economic, social, demographic, political and psychological8. Owing to this complexity, there is no single method that can be used to measure vulnerability and any method used needs to consider all aspects in a comprehensive manner.

Reducing vulnerability is one of the biggest opportunities to reduce disaster risk, as reducing the frequency and magnitude of natural hazards directly. Vulnerability is subject to change over time as it depends on many dynamic processes, such as urbanisation, environmental degradation, demographic change etc 10. Approaches that might help with reducing vulnerability might include policy implementations such as building codes, insurance and social protection improved levels of knowledge, awareness and disaster preparedness 5.