Natural Hazards

Hazard Clusters


Although there are a number of hazard clusters (defined by UNDRR), we focus on the following two as the impact and scale of disasters from is the most common.

Meteorological and hydrological hazards

Meteorological and hydrological hazards are those resulting from the state and behaviour of the Earth’s atmosphere, its interaction with the land and oceans, the weather and climate it produces, and the resulting distribution of water resources. According to EMDAT, from 1979 to 2019, 50% of all recorded disasters (including technological and ‘complex’ disasters), 56% of deaths and 75% of economic losses are attributed to weather, climate and water-related hazards


Geohazards are hazards with a geological origin. They have been divided into three hazard clusters, two of which – seismogenic and volcanogenic – are the result of Earth’s internal geophysical processes, and a third – shallow geohazards – are the result of surface or near-surface processes, generally resulting in erosion or some type of mass movement. Seismogenic hazards, commonly referred to as earthquakes, give rise to specific hazards such as ground shaking, subsidence or ground rupture, but can also trigger hazards such as tsunami or rock fall. Volcanogenic hazards give rise to a wide range of hazards from lava.


Specific Meteorological and hydrological hazards 


Temperature extremes

Heat waves are most deadly in mid-latitude regions during the warmer months of the year. They are characterized by a number of days in a row where the temperatures are significantly above the long term average both day and night. The oppressive air mass in an urban environment can result in many deaths, especially among the very young, the elderly and the infirm. In 2003, much of western Europe was affected by heat waves during the summer months. In France, Italy, The Netherlands, Portugal, Spain and the United Kingdom, they caused some 40 000 fatalities. Extremely cold spells are also dangerous causing hypothermia and aggravating circulatory and respiratory diseases in those vulnerable to this risk.

Floods and flash floods

Floods can occur anywhere after heavy rain events. All floodplains are vulnerable and heavy rain or thunderstorms can cause flash flooding in any part of the world. Flash floods can also occur after a period of dry conditions when moderate or heavy rain falls onto very dry, hard ground that the water cannot penetrate. Floods come in a number of forms, from small flash floods to sheets of water covering extensive areas of land. They can be triggered by severe thunderstorms, tropical cyclones, large low pressure systems , monsoons, ice jams or melting snow. In coastal areas, storm surge caused by tropical cyclones, tsunamis, or rivers swollen by exceptionally high tides can cause flooding. Dikes or flood levees can overtop causing floods when the rivers carry large amounts of snowmelt. Dam breaks (such as in Lybia in 2023) or sudden regulatory operations such as the release of water for hydro-electric power generation can also cause catastrophic flooding. Floods threaten human life and property worldwide. Some 1.5 billion people were affected by floods in the last decade of the 20th century.


Landslides and mudslides

Mudslides and landslides are local events and usually unexpected. They occur when heavy rain or rapid snow or ice melt or an overflowing crater lake loosens vulnerable parts of the landscape on steep slopes, resulting in large amounts of earth, rock, sand or mud flowing swiftly down slope. Hillsides or mountain sides that  are bare or have had their vegetation cover degraded  through clearance or by forest or brush fires may be especially at risk. They can reach speeds of over 50 km/h and can bury, crush or carry away people, objects and buildings. In Venezuela in 1999, after two weeks of continuous rain, landslides and mudflows slid down a mountain, destroying towns and causing an estimated 15 000 fatalities.

Thunderstorms Lightning and Tornadoes

All thunderstorms give rise to sudden electrical discharges in the form of lightning and they often bring rain and gusty winds. Severe thunderstorms are associated with all or combinations of heavy rain,  large hail, very strong winds and occasionally tornadoes or snow. Tornadoes are particularly common in the Great Plains of North America but they can and do occur anywhere, especially in temperate latitudes. Their extremely strong rotating winds can cause severe damage. Other associated phenomena include extremely strong winds from downbursts and flash floods. Worldwide, lightning during dry periods is a significant factor in starting wildfires in forests and grasslands.

Heavy rain and snow

Heavy rain and snow are dangerous for vulnerable communities. They can exacerbate rescue and rehabilitation activities after a major disaster, such as the earthquake in Pakistan in October 2005. They bring havoc to road and rail transportation, infrastructure and communication networks. An accumulation of snow can cause the roofs of buildings to collapse. Strong winds are a danger for aviation, sailors and fishermen, as well as for tall structures such as towers, masts and cranes. Blizzards are violent storms combining below-freezing temperatures with strong winds and blowing snow. They are a danger to people and livestock. They cause airports to close and bring havoc to roads and railways.

Early Warnings for All


To put this in context globally, extreme weather, climate and water-related events caused 11,778 reported disasters over last 50 years, with just over 2 million deaths and $4.3 trillion in economic losses.

To help reduce this for the future, in 2022 the UN established “Early Warnings for All” to ensure everyone on Earth is protected from hazardous weather, water, and climate events through life-saving early warning systems by the end of 2027.

The United Nations UN Climate Ambition Summit in New York on 20th September, opened by Secretary General, was to renew emphasis in reaching this strategic goal.

This is an ambitious push, as timely and accurate climate information is the first line of defence before disaster strikes. The more we scale up early warning systems, the more lives we save and the more livelihoods we protect. Early warning by 24 hours can cut the ensuing damage by 30 per cent

One-third of the world’s people, mainly in the least developed countries and small island developing states, are still not covered by early warning systems. Portugal has multi hazard warning systems, but many countries in southern Europe do not (2022 data)

Countries with limited early warning coverage have disaster mortality that is eight times higher than countries with substantial to comprehensive coverage

At the UN Climate Ambition Summit in New York on 20th September, was to renew emphasis to reach this strategic goal. Achieving Early Warnings for All requires targeted investments of US$3.1 billion over the next four years – around 50 cents for each person to be covered. This is a feasible and achievable sum to protect everyone in the face of rapidly rising climate risks.

The Summit was a call for donors to help provide the support needed to make this ambitious initiative a reality.

Back to Climate Change Home page