A disaster is an event that causes such serious harm to people, buildings, economies, or the environment that the affected community cannot manage without external assistance or relief. The United Nations Office for Disaster Risk Reduction defines a disaster as "a serious disruption of the functioning of a community or a society at any scale due to hazardous events interacting with conditions of exposure, vulnerability and capacity, leading to one or more of the following: human, material, economic and environmental losses and impacts". Natural disasters like avalanches, floods, earthquakes, and wildfires are caused by natural hazards. Human-made disasters like oil spills, terrorist attacks and power outages are caused by people. It may be difficult to separate natural and human-made disasters because human actions can make natural disasters worse. Climate change also affects how often disasters due to extreme weather hazards happen.
Disasters usually affect people in developing countries more than people in wealthy countries. Over 95% of deaths from disasters happen in low-income countries, and those countries have higher economic losses compared to higher-income countries. For example, the damage from natural disasters is 20 times greater in developing countries than in industrialized countries. This is because low-income countries often do not have well-built buildings or good plans to handle emergencies.
To reduce the damage from disasters, it is important to be prepared and have fit-for-purpose infrastructure. Disaster risk reduction (DRR) aims to make communities stronger and better prepared to handle disasters. It focuses on actions to reduce risk before a disaster occurs, rather than on response and recovery after the event. DRR and climate change adaptation measures are similar in that they aim to reduce vulnerability of people and places to natural hazards.
When a disaster happens, the response includes actions like warning and evacuating people, rescuing those in danger, and quickly providing food, shelter, and medical care. The goal is to save lives and help people recover as quickly as possible. In some cases, national or international help may be needed to support recovery. This can happen, for example, through the work of humanitarian organizations.
The United Nations defines a disaster as "a serious disruption of the functioning of a community or a society at any scale". Disasters result from hazards occurring in areas where people live under exposed or vulnerable conditions. Human factors such as inadequate planning, poor development practices, and lack of preparedness can increase community vulnerability to climate hazards.
Disasters are defined as events that have significant adverse effects on people. When a hazard overwhelms the capacity of a community to respond or causes widespread injury or damage, it is classified as a disaster. The international disaster database EM-DAT defines a disaster as âÂÂa situation or event that overwhelms local capacity, necessitating a request for external assistance at the national or international level; it is an unforeseen and often sudden event that causes great damage, destruction, and human suffering.âÂÂ
The effects of a disaster encompass human, material, economic, and environmental losses and effects.
UNDRO (1984) defined a disaster in a more qualitative fashion as "an event, concentrated in time and space, in which a community undergoes severe danger and incurs such losses to its members and physical appurtenances that the social structure is disrupted and the fulfilment of all or some of the essential functions of the society is prevented." Like other definitions, this looks beyond the social aspects of the disaster impacts. It also focuses on losses. This raises the need for emergency response as an aspect of the disaster. It does not set out quantitative thresholds or scales for damage, death, or injury.
A study in 1969 defined major disasters as conforming to the following criteria, based on the amount of deaths or damage: at least 100 people dead, at least 100 people injured, or at least $1 million damage. This definition includes indirect losses of life caused after the initial onset of the disaster. These could be the effects of diseases such as cholera or dysentery arising from the disaster. This definition is still commonly used. However, it is limited to the number of deaths, injuries, and damage in money terms.
The scale of a disaster matters. Small-scale disasters only affect local communities but need help beyond the affected community. Large-scale disasters affect wider society and need national or international help.
Sendai Framework for Disaster Risk Reduction (2015âÂÂ2030)
It is usual to divide disasters into natural or human-made. Recently the divide between natural, man-made and man-accelerated disasters has become harder to draw. Some manufactured disasters such as smog and acid rain have been wrongly attributed to nature.
Disasters with links to natural hazards are commonly called natural disasters. However experts have questioned this term for a long time.
Human-made disasters are serious harmful events caused by human actions and social processes. Technological hazards also fall into this category. That is because they result in human-instigated disasters. Human-made hazards are sometimes called anthropogenic hazards. Examples include criminality, social unrest, crowd crushes, fires, transport accidents, industrial accidents, power outages, oil spills, terrorist attacks, and nuclear explosions/nuclear radiation. Catastrophic climate change, nuclear war, and bioterrorism also fall into this category.
Climate change and environmental degradation are sometimes called socio-natural hazards. These are hazards involving a combination of both natural and human factors. All disasters can be regarded as human-made, because of failure to introduce the right emergency management measures.
Famines may be caused locally by drought, flood, fire or pestilence. Long-lasting local shortages, especially during the modern era, are generally due to government mismanagement, violent conflict, or an economic system that does not distribute food where needed.
Complex disasters, where there is no single root cause, are more common in developing countries. A specific hazard may also spawn a secondary disaster that increases the impact. A classic example is an earthquake that causes a tsunami. This results in coastal flooding, damaging a nuclear power plant on the coast. The Fukushima nuclear disaster is a case in point. Experts examine these cascading events to see how risks and impacts can amplify and spread. This is particularly important given the increase in climate risks.
Some researchers distinguish between recurring events like seasonal flooding and unpredictable one-off events. Recurring events often carry an estimate of how often they occur. Experts call this the return period.
The effects of a disaster include all human, material, economic and environmental losses and impacts.
The Emergency Events Database (EM-DAT) records statistics about disasters related to natural hazards. For 2023, EM-DAT recorded 399 disasters, which was higher than the 20-year average of 369.
Injuries
In the immediate aftermath of a disaster, physical injuries are often the most urgent concern. The severity of damage to local infrastructure may require emergency responders and community health workers to establish temporary triage or treatment sites. Among natural hazards, earthquakes are generally associated with the highest number of injuries, compared to events such as floods, storms, wildfires, or tsunamis.
Chronic diseaseâÂÂrelated emergencies
Many disasters disrupt electricity, transportation, and healthcare systems, creating serious risks for individuals with chronic illnesses. People who rely on ongoing medical treatment such as those with diabetes, kidney disease, respiratory conditions, or cardiovascular disorders are particularly vulnerable when access to medication, medical equipment, or healthcare facilities is interrupted.
Hygiene and disease transmission
Damage to essential infrastructure, including water supply systems, sanitation networks, and energy services, can lead to secondary public health risks. Contaminated drinking water, nonfunctional sewage systems, and reduced waste management increase the likelihood of infectious disease outbreaks. Prolonged power outages may also compromise food safety, medication storage, and the safe operation of healthcare facilities.
Food insecurity
Disasters frequently disrupt food production and distribution systems. While supply chains may be temporarily interrupted, damage to agricultural land, livestock, or food processing facilities can create longer-term food shortages. These disruptions may contribute to rising food prices, disproportionately affecting low-income and vulnerable populations.
Mental health effects
Experiencing a disaster can have significant psychological consequences. In the short term, affected populations may experience shock, fear, and grief. Over time, the loss of housing, livelihoods, and social support networks can contribute to mental health conditions such as post-traumatic stress disorder (PTSD), depression, and anxiety. Long-term impacts may also include increased rates of substance misuse.
Damage to healthcare systems
Disasters can severely impair healthcare infrastructure through physical destruction, power failures, or shortages of medical supplies. Hospitals and clinics may be unable to operate at full capacity, while damage to equipment and medication losses further limit care delivery. Population displacement following disasters can also result in healthcare workforce shortages, and in some cases, reduced incentives or resources for rebuilding health facilities.
Between 2016 and 2020 the total reported economic losses amounted to $293 billion. This figure is likely to be an underestimation. It is very challenging to measure the costs of disasters accurately, and many countries lack the resources and technical capacity to do so. Over the 40-year period from 1980 to 2020 losses were estimated at $5.2 trillion.
In 2023, natural hazard-related disasters resulted in 86,473 fatalities and affected 93.1 million people. Whilst the number of deaths was much higher than the 20-year average of 64,148, the number affected was much lower than the 20-year average of 175.5 million.
According to a UN report, 91% of deaths from hazards from 1970 to 2019 occurred in developing countries. These countries already have higher vulnerability and lower resilience to these events, which exacerbates the effects of the hazards.
Hazards such as droughts, floods, and cyclones are naturally occurring phenomena. However, climate change has caused these hazards to become more unreliable, frequent and severe. They thus contribute to disaster risks. Countries contributing most to climate change are often at the lowest risk of feeling the consequences. As of 2019, countries with the highest vulnerability per capita release the lowest amount of emissions per capita, and yet still experience the most heightened droughts and extreme precipitation.
Social, cultural, and political perspectives
Scholarly research emphasizes that disaster outcomes are shaped not only by hazardous events but also by social organization, culture, governance, and political economy. In this view, hazard is one component of risk; impacts (mortality, displacement, recovery) are patterned by exposure, vulnerability, and capacity that develop over time through land use, infrastructure, institutions, and everyday practice These perspectives inform contemporary approaches to disaster risk reduction (DRR), which focus on reducing vulnerability and exposure alongside hazard monitoring.
Cultural approaches in DRR examine how beliefs, social norms, values, and routines influence risk perception, preparedness, warning response, and recovery. Culture is treated as dynamic: people interpret hazards through shared meanings and practices that evolve with experience and institutional context. Programs can fail if they overlook local meanings or organization (e.g., warning formats, shelter rules, or rebuilding standards that conflict with livelihoods or customary tenure). Co-developed, context-sensitive strategies tend to have higher uptake.Cultural framings are also relevant to warning interpretation and âÂÂlast-mileâ communication. People routinely combine official alerts with heuristics, trusted peers, and place-based knowledge when deciding whether to evacuate or shelter in place.Recognizing these practices can improve message design, timing, and the selection of intermediaries (for example, local associations, faith groups, and community radio).
Another strand analyzes preparedness as a form of governance. Institutions construct âÂÂsecurity imaginariesâ shared models of possible threats and appropriate countermeasures and assemble apparatuses intended to function amid uncertainty, such as surveillance networks, stockpiles, expert committees, and emergency operations centers. Preparedness necessarily entails selection: authorities decide which risks to prioritize, which capacities to fund, and how to distribute roles across levels of government and sectors. These choices shape coordination and public expectations of response capability.
In global health, preparedness has included scenario planning, early-warning and surveillance systems, and the maintenance of material reserves to ensure continuity of response when events exceed normal operating conditions.The literature emphasizes that such systems are never exhaustive: they reflect historically specific judgments about plausibility, proportionality, and acceptable trade-offs between objectives (e.g., civil liberties, economic continuity, and protection of life).
Critical disaster studies examines how power, inequality, and historical processes shape risk, loss, and recovery. Rather than treating a disaster as an exogenous shock to an otherwise level playing field, this approach analyzes how colonialism, segregation, uneven development, and policy choices about land use and infrastructure generate differential exposure to harm and unequal access to protection and assistance.
From this perspective, there are no purely âÂÂnaturalâ disasters: hazard interacts with socially produced vulnerability and capacity, which are distributed along lines such as class, race, gender, age, disability, and legal status.
Critical work also attends to questions of representation and voice: whose experiences are documented, which forms of knowledge inform planning, and how media or cultural narratives frame causes and consequences.It further examines the politics of aid and recovery eligibility rules, documentation requirements, and the spatial distribution of assistance and how these practices can reproduce or mitigate pre-existing inequalities.
The word disaster is derived from Middle French ' which comes from Old Italian '. This in turn comes from the Ancient Greek pejorative prefix - (-) "bad" and ('), "star".