Biological disasters are caused by hazards of organic origin, including bacteria, viruses, parasites, mosquitoes carrying disease-causing agents, and toxins or bioactive substances that occur naturally or are deliberately on unintentionally released. These hazards can lead to economic and environmental damage and loss of life, affecting people and animals at the population level as well as crops, livestock and endangered species of flora and fauna.

Epidemic diseases infect millions every year, and the COVID-19 pandemic illustrates the breadth and depth of the transformative impact of biological disasters. The pandemic cost more than a million lives in less than a year, caused widespread disruption to daily life across the world and sparked the deepest economic recession in decades. The 21st century has already experienced several major infectious disease epidemics – old diseases such as cholera and plague have returned, and new ones like severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and H1N1 pandemic influenza have emerged. Further epidemics and pandemics are almost certain; the only unknowns are when and where a new lethal threat will emerge. Examples of other recent outbreaks, epidemics or pandemics include Ebola in the Democratic Republic of Congo (2018–2020) and West Africa (2013–2016), and the Zika virus in the Americas and Pacific regions (2015–2016).

Risk factors

Biological disasters are driven by a complex set of factors ranging from the ease of spread of biological hazards to people’s exposure to those hazards, their susceptibility to becoming infected and the capacity of individuals, communities, countries and international actors to reduce risks and manage the consequences of outbreaks. The COVID-19 pandemic showed the need for international cooperation and comprehensive multi-dimensional policy responses incorporating health facilities, social management and messaging, economic interventions, technology-based solutions, and responsive governance.

SARS-CoV-2, the coronavirus that causes COVID-19 is zoonotic, that is, it was transmitted to humans from animals. Many newly emerging or re-emerging viral infections, including Ebola, plague, Zika, SARS and MERS are zoonoses. Agricultural practices, animal husbandry, food production, changes in land use, hunting practices, deforestation and ecosystem breakdown have all been identified as contributing to the rising risk of zoonotic infections.

Vulnerable areas

Biological hazards affect people at all levels of society and in all countries because infectious diseases travel easily across borders. New pathogens continue to emerge by mutating, adapting and travelling from one species to another. Biological hazards can be endemic, that is constantly present in a community – they pose low risk when the population is largely immune, but risk becoming epidemics when they are introduced to a new host community with no immunity.

The HIV/AIDS pandemic, which has claimed more than 32 million lives since it was identified in 1981, shows how biological hazards often exploit the fault lines of society, spreading in the shadows of marginalization, disruption and conflict. Droughts, floods, earthquakes and large displacements of populations also create conditions favourable for disease transmission.

The following are UNDRR’s key messages on the COVID-19 pandemic, issued in the first half of 2020:

Prevention saves lives

• Prevention saves lives: it is never too late for countries to take significant and bold preventive actions to stop the spread…and never too early to start.

• COVID-19 is testing our resilience: we need to work together to support individuals, communities and economies to react, rebound and recover better.

• Viruses don’t need passports and in our global society, they thrive when we don’t apply a collective and unified approach. Global systems such as trade, travel and finance interconnect more and more. We need an all-of-government, all-of-society, all-of-world approach if we are to defeat COVID-19 and other pandemics.

Protect the most vulnerable

• COVID-19 does not discriminate, but its impact does. Governments must identify the most vulnerable in their countries and dedicate budgeted resources to prevent the spread of COVID 19 and support high-risk groups, including older persons, women, day workers and the poor; persons living with disabilities; migrants and displaced populations; and slum dwellers and the homeless.

• A threat to one of us, is a threat to all of us. We are only as strong as the weakest: we must leave no one behind. Developed countries with more resources available to respond to the outbreak need to attend first and foremost to the safety and well-being of their own citizens but must extend international support to low- and middle-income countries that are struggling to cope with the outbreak.

Back to normal is not good enough: we must recover and build back better

• Because the nature of risk has changed: it is systemic, joined-up, and cascading. One risk transforms into another, exposing and exacerbating existing vulnerabilities.

  We see this with #COVID-19: a biological hazard making clear the precarious systems upon which trade, food, energy, transportation, and social safety nets rely. The UN flagship report on risk – the Global Assessment Report – GAR (May 2019), highlighted this.

• So, we must fight systemic risk with a systemic approach. We cannot work in silos. We must map risk from many angles and work in a collaborative, trans-boundary way since hazards do not respect borders or politics. Solutions are needed across sectors such as water, sanitation and hygiene; education; health and nutrition; livelihoods; child and social protection; shelter and housing; and public open spaces.

• Recovery must seek to build the resilience of public and private systems, and planning must start now. The challenges presented by this disaster will form the basis for new plans and designs to ensure public and private systems are made resilient in the face of future hazards.

• This is the opportunity to build resilience into COVID-19 recovery plans. National and local governments must factor in biological hazards and risks in their national and local disaster risk reduction strategies (Sendai Framework Target (e)).

Protect the most vulnerable

• COVID-19 does not discriminate, but its impact does. Governments must identify the most vulnerable in their countries and dedicate budgeted resources to prevent the spread of COVID 19 and support high-risk groups, including older persons, women, day workers and the poor; persons living with disabilities; migrants and displaced populations; and slum dwellers and the homeless.

• A threat to one of us, is a threat to all of us. We are only as strong as the weakest: we must leave no one behind. Developed countries with more resources available to respond to the outbreak need to attend first and foremost to the safety and well-being of their own citizens but must extend international support to low- and middle-income countries that are struggling to cope with the outbreak.

Crisis leads to opportunity

• This crisis has given us a huge opportunity. It makes us rethink the way we work, educate our children, and even our cultural customs. If there was ever a time to realign towards social, economic and environmental sustainability, it is now.

• We must learn from what is working. There may be secondary or seasonal waves and there will be more viruses and more disasters. We need to factor in governance, community resilience, and global best practice.

• Risk does not occur in silos. We must have a coordinated approach to understanding and reducing risk across borders and within governments.

• COVID-19 has demonstrated the need for a whole-of-government approach that leverages the capacities of all relevant line Ministries, including National Disaster Risk Management Agencies.

• The scale of the disaster requires new ways of working, and innovative partnerships to ensure interventions go to scale and efforts to prevent transmission reach down to the community level, where impact will be greatest.

Droughts refer to extended periods of below-normal rainfall. They are a weather-related natural hazard, which can affect vast regions for months or years, with a significant impact on economic performance, particularly food production. Millions of people are affected by droughts each year and it is expected that vulnerability to drought will increase due to population increases, environmental degradation, development pressures and climate change.

There is little, if anything, that can be done to alter the occurrence of droughts. However, it is important that scientists try to understand and communicate the probability of drought events of various levels of intensity and duration.

Droughts can be defined in different ways:

• Meteorological drought – a measure of departure of precipitation from normal; due to climatic differences what is considered a drought in one location may not be a drought in another location.
• Agricultural drought refers to a situation when the amount of moisture in the soil no longer meets the needs of a particular crop.
• Hydrological drought occurs when surface and subsurface water supplies are below normal.
• Socio-economic drought refers to the situation that occurs when physical water shortage begins to affect people.
• The World Meteorological Organization (WMO) has recently adopted the Standardized Precipitation Index (SPI) as a global standard to measure meteorological droughts on the basis of rainfall data.

Risk factors

Drought risks are not only associated with deficient or erratic rainfall but with poverty and rural vulnerability, poor water and soil management, weak or ineffective governance and climate change. Climate change will contribute to a shortage of rainfall and consequently desertification.

Vulnerable areas

Droughts affect all climactic regions, but parts of Africa are among the most vulnerable. For example, in the African Sahel, warmer and drier conditions have led to a reduced growing season with detrimental effects on crops. In southern Africa, longer dry seasons and more uncertain rainfall are prompting adaptation measures. Poor rural households, whose livelihoods depend on rain-fed subsistence agriculture are the social groups most exposed and vulnerable to drought. Droughts are rarely, or solely, responsible for conflicts, but they can contribute to the likelihood of conflict by increasing competition for scarce resources and by exacerbating ethnic tensions usually due to displacement or migration.

Until the arrival of COVID-19, earthquakes were the natural hazard that caused most deaths per event. EM-DAT figures shows that earthquakes claimed more than 720,000 lives between 2000 and 2019. More than 3 billion people live in regions prone to earthquakes.

Most earthquakes are caused by the movement of the earth’s 15 tectonic plates. Geophysicists can identify places where earthquakes are sure to happen, but nobody can predict when an earthquake will happen, or its severity. Seismologists register more than 30,000 tremors every year, but most of these are of low magnitude.

Risk factors

Many factors aggravate earthquake risks, including:

• Population density - eight out of the 10 most populated cities in the world are prone to earthquakes. Most of the world’s earthquakes occur around the Pacific Rim and many of these cities are in Asia where two-thirds of the world’s population lives.
• Poorly built and non-engineered buildings.
• Poverty – constrains more people to live in crowded, sub-standard housing and unsafe places. Earthquakes hurt the poor more than the rich, because education and high building standards can save lives, whereas ignorance and corruption can cost lives.

The Richter Scale

The ranking system used to measure earthquake magnitudes is called the Richter Scale. Developed by Charles Richter in 1935, this scale is used to measure earthquake magnitude. It indicates the energy released by an earthquake. Another ranking system, the Modified Mercalli Intensity Scale, measures seismic intensity. The magnitude of an earthquake is a measured value of the earthquake size. The intensity of an earthquake is a measure of the shaking created by the earthquake; this value varies with location.

Richter Scale Categories:

Floods affect more people than any other hazard. Worldwide, nearly 200 million live in coastal zones at risk of flooding. Flooding is usually the result of heavy or continuous rain that exceeds the absorptive capacity of the soil and the flow capacity of rivers, streams and coastal areas. Floods can be triggered by thunderstorms, tornadoes, tropical cyclones, monsoons, melting snow and dam breaks. The most common floods are flash floods, snowmelt floods, coastal floods and river floods. Flash floods and sudden floods are the most dangerous, especially when they occur at night.

Risk factors

Rapid population growth, rapid urbanization, environmental degradation such as the loss of forests and natural flood buffers, and climate change, will expose more people to future floods. Melting glaciers and rising sea levels will bring floods to places not previously at risk.

Vulnerable areas

Developing countries are most at risk and although Asia remains the continent most hit by floods, Africa and Latin American countries are also heavily affected.

The poor, with the least means to adapt are often forced to live in high-risk places: slopes, flood plains, ravines, or in crowded, urban low-lying areas in mega-cities.

A heatwave is a prolonged period of extremely high temperatures. They vary according to location of a particular region and the time of year and there is no universal way of defining or measuring heat waves. Heatwaves are often accompanied by high humidity and can exacerbate urban air pollution which can affect the elderly, pregnant women and children.

The impacts of heatwaves can be very catastrophic as we saw in India in May 2015, where at least 2,500 people died of the consequences of high temperatures reaching over 45 degrees Centigrade. Europe was also badly affected by high and unusual temperatures in the summer of 2003 leading to health crises in several European countries and killing a total of 70,000 people, mostly older persons.

Vulnerable areas

Regions that are more susceptible to heat waves include inland deserts, semi deserts and Mediterranean-type climates.

Cities are particularly vulnerable to heatwaves as urban areas experience higher temperatures during the summer due to buildings, roads, and other infrastructures absorbing solar energy. Heat waves disproportionately impact people who are poor, elderly and young.

Hurricanes, tropical cyclones and typhoons affect millions every year, and in the future they are likely to be more severe although possibly less frequent due to global warming.

Hurricanes induce severe flooding and storm surge, and combined coastal inundation thus cause catastrophic damage along coastlines and several hundred miles inland. Hurricanes Mitch and Katrina are among the worst Atlantic hurricanes in history; Mitch killed 11,000 people in 1998 and caused extreme damage, estimated at over US$6.5 billion. In 2005, Katrina killed more than 1,800 people and cost US$130 billion in damages.

Tropical cyclones, hurricanes and typhoons, although named differently, describe the same hazard type. They are referred to as tropical cyclones in the Indian Ocean and South Pacific, hurricanes in the Atlantic and eastern North Pacific, and typhoons in the western North Pacific. In the north Atlantic and the Caribbean, August and September are usually peak months of the hurricane season, which spans from June through t November. In the eastern North Pacific, the season starts in mid-May and finishes in November. The North Indian Ocean cyclone season  is between April and December, with peaks in May and October.

Risk factors

Climate change, environmental degradation and coastal developments including urbanization in coastal areas will make more population to be exposed to threats by tropical cyclones in the future.

Vulnerable areas

Coastal areas are the most hurricane-prone. Tropical cyclones are generally accompanied with heavy rains and severe flooding and, in coastal areas with shallow slant bathymetry and flat plain, with storm surges that may threaten tens of thousands of people living by the sea. China, Bangladesh, India, Japan, the Philippines, the USA and the Caribbean are the most affected each year by this kind of disaster. The most vulnerable populations are those who are living in poor buildings and fragile constructions in the coastal zones.

Hurricanes are ranked according to the Saffir-Simpson hurricane scale, which classifies the damage caused by hurricanes to wind speed. Hurricanes can inflict terrible damage even from their formative stage.

Asia is the continent most affected by landslides; the Americas suffer more deaths, and Europe bears the most economic losses with an average economic loss of almost US$ 23 million per landslide.

Landslides can reach speeds of over 50 km/h and can bury, crush or carry away people, objects and buildings. Landslides cannot be predicted but warning systems measuring rainfall levels can provide warning to people living in landslide-prone areas.

Landslides can be triggered by geological and physical causes such as glacier or snow melts, heavy rains and water pressure, earthquakes, volcanic eruptions and overly steep slopes. Landslides can also be triggered by human action, the most common being building on unstable slopes. Submarine landslides, or massive slides and rock falls hitting the sea can also cause tsunamis.

Risk factors

Population growth, rapid urbanization and environmental degradation (deforestation and inappropriate use of lands and slopes) are increasing landslide risk and exposing more people to landslide danger. High population density, heavy rainfall and rapid land use changes increase the instability of slopes, making people more vulnerable to landslides.

Technological systems are complex, with many dependent subsystems. The failure of one element within this system can cascade throughout the chain, causing a series of failures leading to a disaster. Technological hazards are increasing due to the scope of technological expansion. They include industrial activity that includes dangerous conditions, processes, chemicals or toxic materials, all transport systems (land, sea, air), defensive or offensive weapons systems, nuclear materials in civilian facilities such as power plants, and the misuse of chemical or nuclear weapons.

A new set of emerging technological risks under the Sendai Framework include ICT-related hazards. The increasing dependence upon complex large-scale network architectures of information technologies also increases exposure to cyber security threats. These threats include computer viruses, worms, Trojan horses, malware, spoofing attacks, identity theft, the theft and illegal disclosure of data, the loss of data and contamination of data. They have the potential to disrupt essential infrastructure operations such as communication, health, banking, transportation, energy, education and many other services.

Risk factors

In many countries, industrial hazards are exacerbated by ageing, abandoned or idle installations. These problems are amplified by insufficient institutional and legal capacities to deal with technological risk reduction.

Natural hazards – for example, storms, landslides, floods or earthquakes – can also cause industrial accidents by triggering the release of hazardous substances from industrial facilities that are located within their path of destruction. The cascading effect of natural hazards triggering technological disasters are called NATECH accidents. The Great East Japan earthquake and tsunami and subsequent Fukushima Daiichi nuclear accident in 2011 put NATECH risks on the global agenda. NATECH events are a recurring but often overlooked feature in many disaster situations. Instruments for reducing technological risks, such as chemical accident prevention and preparedness programmes, often tend to overlook the specific drivers of NATECH events, leaving an important gap in managing this type of risk.

Vulnerable areas

Most industrial accidents entail the release of hazardous substances into the atmosphere or water bodies with grave impacts on health and human safety. Residential communities around industrial establishments tend to be most at risk because of their proximity, as in the case of Bhopal disaster in India in 1984 where a gas leak from a pesticide plant resulted in more than 15,000 deaths and more than 100,000 people affected from the areas around the facility.

Another example is the collapse of two tailing management facilities (TMFs) – essentially large dams storing chemical waste – in Bento Rodrigues, Brazil, in 2015. A toxic slick comprised of 40 million m3 of waste laden with heavy metals swept 650 km down the Doce River basin, flooding villages downstream, causing 19 deaths and contaminating 2,200 ha of land. The disaster revealed critical gaps in regulation, monitoring, enforcement, information flow, early warning, response and coordination mechanisms between the operator and authorities at all levels. In early January 2019, another TMF dam failure in Brumadinho, Brazil, caused the death of 186 people, with a further 122 missing. The ecosystem of the affected areas is believed to have been damaged permanently.

Tornadoes kill fewer than 100 per year on average but they can be very destructive and cause huge economic losses. The United States is a major hotspot with about 1,000 tornadoes every year, causing 80 deaths and more than 1,500 injuries per year.

Tornadoes are vertical funnels of rapidly spinning air. Their winds may top 400 km/h and can clear-cut a pathway of more than 1 km wide and 80 km long. Most tornadoes are about 100 meters wide; larger tornadoes can be 1 km wide and travel for 50 km or more. Tornado size does not necessarily indicate how destructive it is. Small tornadoes can also be very destructive. Tornadoes have many distinct shapes, sizes, colours and intensities.

Risk factors

Lack of early warning systems and preparedness programmes increase the risk for all populations. However, even when warning systems are in place, the aged and children have higher mortality rates given their lower capacity to respond. Populations living in mobile homes are at greater tornado risk. The rate of serious injury for mobile homes occupants is 85.1 per 1,000 compared to 3 per 1,000 for occupants in standard homes.

Vulnerable areas

The most tornado-prone areas in the world are in North America, in particular the Great Plains in the United States and south-central Canada. Tornado Alley, a region that includes eastern South Dakota, Nebraska, Kansas, Oklahoma, northern Texas and eastern Colorado, is home to the most powerful and destructive of these storms.

The United States gets 75 per cent of all the world’s tornadoes, followed by Canada and Bangladesh. Australia, New Zealand, South Africa, India, Argentina and the Russian Federation are also prone to strong tornadoes.

Communities living in poorly built houses close to potential flying objects are in particular danger. People outdoors when tornadoes occur are at higher risk of mortality.

The Enhanced Fujita Tornado Scale

The Fujita Scale is named for Dr TT (Ted) Fujita, who made the first systematic study of tornado forces; it was replaced by the Enhanced Fujita (EF) Scale in February 2007.

The Pacific is by far the most active tsunami zone, according to the US National Oceanic and Atmospheric Administration (NOAA), but tsunamis have been generated in the Caribbean and Mediterranean seas, and the Indian and Atlantic oceans.

The term tsunami comes from the Japanese word for “harbour wave” and is a series of giant, long ocean waves created by an underwater disturbance such as an earthquake, landslide, volcanic eruption or meteorite; it consists of a series of 10 or more waves with crests arriving every 10 to 60 minutes. Tsunami waves can be very long (as much as 100 km) and tens or even hundreds of metres high. They can cross entire oceans without great loss of energy. The Indian Ocean tsunami travelled nearly 5,000 km to Africa, arriving with enough force to kill people and destroy property.

The most destructive tsunamis are generated by large, shallow earthquakes with an epicentre or fault line near, or on the ocean floor. Usually, it takes an earthquake with a Richter magnitude exceeding 7.5 to produce a destructive tsunami. Receding water is one of the first visual signs of a tsunami. Experts believe that a receding ocean may give people as much as five-minutes warning to evacuate the area.

Risk factors

More people are living by the sea, in earthquake-prone zones, in poor quality buildings, all of which makes more people vulnerable to a tsunami. The destruction of the environment and natural barriers and the lack of coastal land-use planning are factors that aggravate tsunami impacts. The development of tourist settlements in tsunami-prone zones with no tsunami risk assessment also increases vulnerability.

Vulnerable areas

All oceanic regions of the world can experience tsunamis, but in the Pacific Ocean and its marginal seas, there is a much more frequent occurrence of large, destructive tsunamis because of the many large earthquakes along the margins of the Pacific Ocean.

Further information

Key reference materials

Plans and Procedures for Tsunami Warning and Emergency Management, UNESCO 2017.

Tsunami Glossary, UNESCO 2019.

Tsunami Warning Map, UNESCO 2020.

There are more than 1,500 volcanoes potentially active in the world and more than one million volcanic vents under the sea; about 50-60 volcanoes erupt every year worldwide.

A volcano is an opening, or rupture, in the planet’s crust, which allows hot, molten rock, ash and gases to escape from deep below the surface. Volcanic eruptions can be ranked along a spectrum from quiet (effusive) to violent activity, from non-explosive, slow-moving lava flows to explosive eruptions that blast material into the air. The violence of the eruption is determined mainly by the amounts and rate of effervescence of the gases and by the viscosity of the magma itself.

Volcanoes produce a wide variety of natural hazards that can kill people and cause huge economic losses. Avalanches generated by large masses of volcanic cone sliding into the sea can trigger a tsunami. Compared to other natural hazards, such as earthquakes, volcanic eruptions cause generally fewer deaths as eruptions are often predictable and people can be evacuated in time.

Risk factors

Although recent decades have seen remarkable progress in monitoring active volcanoes, volcano risk is increasing due to rapid urbanization and the high density of populations living on volcano slopes and valleys. About 500 million people worldwide are exposed to volcano risk and more than 60 large cities are located near active volcanoes. Volcanoes with a high hazard potential are located mainly in developing countries around the circum-Pacific belt (part of Asia, Latin America, the Caribbean and Southwest Pacific.)

Vulnerable areas

Populations living close to a volcano with no monitoring and early warning systems are the most vulnerable to volcano eruption. Poor people are among the most vulnerable as they are often economically constrained to live in high-risk zones such as on the slopes of an active volcano or in nearby valleys and less prepared to cope with disasters.

People living near volcanoes will be the most vulnerable and forced to abandon their land and homes, sometimes forever. People living far away from the eruption can be affected as their cities and towns, crops, industrial plants, transportation systems, and electrical grids will be damaged by tempura, ash, lahars and flooding.

Wildfires are not a major cause of death, but they can be very destructive. Many wildfires are caused by human activities, either accidentally or as a consequence of carelessness, or arson. These fires often get out of control and spread over vast areas extending to tens or hundreds of thousands of hectares.

Risk factors

The Global Fire Monitoring Centre, which is monitoring worldwide fires, is projecting increasing fire risk in the future due to increasing demand for agricultural lands for food and the necessity to use fire for land-use change, the expansion of residential areas/infrastructures built near fire-prone vegetation, and extended periods of drought. Wildfires will cause more land degradation (soil erosion, loss of land productivity) and as a consequence will create more flooding and landslides.

Vulnerable areas

Agricultural and pasture lands in which fire is used for controlling weeds, bush encroachments, and for land clearing are the most wildfire-prone areas as well as fire-prone natural forest, bush land and grassland ecosystems with high occurrence of natural fires in the subtropics (e.g. Africa, Australia), or in the northern latitudes (e.g. North America, Russia), and agricultural and forest plantations (e.g. eucalypt and pine plantations).

Other vulnerable areas include: residential areas or scattered houses/infrastructures nearest to fire-prone vegetation; residential areas or individual structures made of easily flammable materials (e.g. wood, thatch, wooden shingles or otherwise easily ignitable roofing materials); and abandoned rural villages and human settlements with no one to manage, prevent or respond to wildfires.