Cambridge English Dictionary defines hazard as something that is dangerous, and likely to cause damage. As reflected by “likely” in this definition, the term hazard suggests possibility of damage, even though actual damage has not been caused. Mere existence of the damage causing potential is thus enough to identify a process, phenomenon, or activity as hazard.
Hazard thus refers to loss causing potential, and not actual loss. Of the many hazards present around us, some could be associated with electricity, fire, water, as also different chemicals present in our restroom, laundry or store. Petrol, kerosene, and cooking gas could also be identified as hazards. You might not at first consider some of these as being hazard, but in depth review would convince you of their loss causing potential.
When identifying water as a hazard, it refers to scarcity or abundance of water that could cause wilting, crop loss, drought, flood, or landslide. Likewise medicines casually kept over the shelf in your house could be a hazard, especially if these are expired or get into the hands of children. Cooking gas could be another hazard present in your house.
The term ‘peril’ is sometimes used instead of hazard, particularly in the insurance industry.
A hazard is formally defined as a process, phenomenon or human activity that has the potential to cause loss of life, injury or other health impacts, property or infrastructure damage, socio-economic disruption or environmental degradation. Hazards may be natural, or anthropogenic in origin.
Importance of identifying hazards can be better appreciated from the fact that effective disaster risk reduction requires the consideration of not just what has happened, but also what could happen. Most disasters that could happen have actually not yet happened.
Natural or physical events are termed hazard when these have the potential to harm people or cause property damage, and socio-economic disruption. The spatial distribution of natural hazards primarily depends on natural processes that include movement of the tectonic plates, influence of weather systems, and the existence of waterways, and slopes. But then, processes such as urbanisation, environmental degradation, and climate change can also influence the location, frequency, and intensity of natural hazards. These processes are known as risk drivers.
These hazards have their origin in internal earth processes, and the examples include earthquake, volcanic activity, emissions, and related geophysical processes. Tsunami is difficult to categorise – although triggered by undersea earthquakes these essentially become an oceanic process that is manifested as a coastal water-related hazard.
These have atmospheric, hydrological or oceanographic origin, and the examples include cyclone, flood, drought, and heat wave. Hydro-meteorological conditions might also be a factor in other hazards such as landslides, wildfires, locust plagues, epidemics, and transport and dispersal of toxic substances and volcanic eruption material.
These are of organic origin or conveyed by biological vectors, including pathogenic microorganisms, toxins, and bioactive substances. Examples include bacteria, viruses or parasites, as well as venomous wildlife, and insects, poisonous plants, and mosquitoes carrying disease-causing agents.
These may include chemical, natural, and biological hazards, and could be created by environmental degradation or physical or chemical pollution of air, water, and soil. However, many of the processes, and phenomena falling in this category might be termed drivers of hazard, and risk rather than hazards in themselves, such as soil degradation, deforestation, biodiversity loss, salinization, and sea-level rise.
These originate from technological or industrial conditions, dangerous procedures, infrastructure failures or specific human activities, and the examples include industrial pollution, nuclear radiation, toxic wastes, dam failures, transport accidents, factory explosions, fires, and chemical spills. Technological hazards might also arise directly as a result of the impact of a natural hazard.
Hazards sometimes trigger a sub-set of hazards, for instance earthquake can trigger landslides, landslide can cause river blockade causing flood, cyclone can bring intense winds, storm surge, and heavy rainfall, as well as trigger secondary hazards, such as landslides. The series of triggering relationships can cause a domino or cascading effect, as was observed in case of the tsunami–earthquake–nuclear crisis in Japan after magnitude 9.0-9.1 Great East Japan Earthquake of March 11, 2011
Natural hazards are characterized by their magnitude or intensity, speed of onset, duration, and the area of impact.
Hazard intensity or magnitude varies over different time scales, and is often expressed in terms of probabilities or return periods or recurrence intervals. The hazards with longer return period (less frequent) generally have higher intensity. Because of long return periods, the communities are often unaware of the potential threat of high intensity hazards.
This was the situation with Mt. Pinatubo in Philippines whose eruption history was unknown. It was heavily eroded, and obscured from view by dense forests, which supported a population of several thousand indigenous Aetas. Mt. Pinatubo however erupted on June 15, 1991, and it was the second largest terrestrial eruption of the 20th century after June 6-8, 1912 eruption of Novarupta in Alaska. Eruption of Mt. Pinatubo triggered large mudslides (known as lahars), which affected people for several years after the eruption, and displaced 20,000 indigenous peoples living in its foothills.
Hazards also occur at different geographical or spatial scales. For instance, the occurrence, and impact of landslides tends to be quite localised, whereas droughts often occur over several tens of thousands of kilometres.
A region is often exposed to multiple hazards, and in such cases it is essential to consider the risk related to the full range of hazards that might affect people or assets. Not doing so could result in people getting exposed to another hazard by mitigation efforts to safeguard them from one.
Hazards can also interact; the June 15, 1991 eruption of Mt. Pinatubo was accompanied by Typhoon Yunya, which soaked the accumulating volcanic ash with rainfall. The weight of the wet ash caused the roofs of homes, and businesses to collapse, resulting in most of the 300 deaths directly associated with the eruption. The interaction of hazards can thus magnify the overall impact, which has major implications for risk assessment.
Hazard assessment begins with identifying hazards relevant for the area of interest, collecting all sort of historical data pertaining to these, and preparing a comprehensive hazard catalogue with date, geographical location, impact, and the like. This could also include secondary (or chains of) hazards triggered by the primary event, a landslide or fire after an earthquake or the interactions between hazards.
Hazard catalogues can be used with risk models in a deterministic or probabilistic manner.
Data pertaining to the historical events is often utilized to assess the impact of past events with current level of exposure using deterministic analyses, as also for estimating the probability of occurrence of a specific intensity hazard at some location.
High intensity hazard incidences however occur infrequently, and have long return periods. This simply implies that some extreme hazard intensities likely in the area have not yet happened. This is particularly relevant for geological hazards like earthquake that occur over long time periods. Historical record of such hazards does not therefore reflect the true picture.
Computer generated hazard events that are consistent with the statistical characteristics of the historical record are therefore utilized to complete the hazard catalogues. Such event sets typically include large number of potential events that define the full range of potential hazard events. Event sets are utilised with information on exposure, and vulnerability to quantify probabilities of loss, and risk from a hazard. A probabilistic risk model contains a compilation of all possible impact scenarios for a specific hazard, and geographical area.
It is important to note that the hazard catalogues are generally associated with rapid onset hazards. Risk assessments for slow onset hazards, such as drought, are typically undertaken using deterministic approaches.
Can we reduce hazards?
The adverse impacts of natural hazards, cannot often be prevented fully, but the severity of these hazards can be substantially reduced by implementing planned strategies. The mitigation measures could include engineering techniques such as hazard-resistant construction as well as improved environmental, and social policies, and public awareness.
Refinement in knowledge, and understanding of hazards coupled with hazard assessments can help in anticipating occurrence of hazard over different time-periods. This anticipation could range from probabilistic analysis of long-term hazard occurrence, to monthly, daily or even hourly detection, and monitoring of hazards so as to provide appropriate input for the early warning systems.
The warning systems should however be accompanied by disaster risk reduction strategies to reduce vulnerability, and enhance the capacity to respond, and recover from a disaster. Effective early warning systems include (i) detection, monitoring, and forecasting of the hazard, (ii) analysis of the risks involved, (iii) dissemination of timely, and authoritative warnings, and (iv) activation of emergency preparedness, and response plans. These need to be coordinated across many agencies at the national, state, and community levels for the system to work – failure in one component, or lack of coordination, could lead to the failure of the whole.
It is not possible currently to forecast the time of an earthquake, but the regions likely to house future earthquakes can be reliably determined. The impact of earthquakes can thus be minimised by implementing strict building codes, and raising awareness on how to respond. The occurrence of landslides can however be predicted based on triggers such as heavy rainfall, and the population likely to be affected can accordingly be warned.