Natural Hazards and Disasters

The One Thing

Natural hazards become disasters when their impacts exceed a community’s capacity to cope. Although hazards cannot always be prevented, disaster losses can be reduced through lower exposure and vulnerability, resilient development, environmental protection, scientific warning systems, community participation, and coordinated disaster management.

Who and What

• Natural hazard: A naturally occurring event or process with the potential to cause loss of life, property damage, or environmental harm.
• Disaster: A serious disruption caused by a hazard that exceeds a community’s ability to cope using its own resources. A hazard becomes a disaster when it produces severe disruption and losses beyond local coping capacity.
• Risk: The possibility of harmful consequences produced by the interaction of a hazard with exposed and vulnerable people or assets. A useful relationship is: Disaster risk = Hazard × Exposure × Vulnerability. Greater preparedness and coping capacity reduce overall risk.
• Vulnerability: Physical, social, economic, and environmental conditions that increase the likelihood of damage.
• Exposure: The presence of people, buildings, infrastructure, livelihoods, or ecosystems in areas that may be affected by hazards.
• Earthquake: Sudden shaking of the Earth’s crust, mainly caused by energy release along faults or tectonic movements. Earthquakes are associated particularly with plate boundaries, active faults, volcanic regions, and zones of crustal instability.
• Focus or hypocentre: The point inside the Earth where an earthquake begins.
• Epicentre: The point on the Earth’s surface directly above the focus.
• Seismic waves: Waves of energy released during an earthquake that travel through the Earth and along its surface.
• Magnitude: A measure of the energy released by an earthquake, commonly expressed using the Richter scale or moment magnitude scale.
• Intensity: A measure of the observed effects and damage caused by an earthquake at a particular place.
• Tsunami: A series of large sea waves usually generated by an undersea earthquake, volcanic eruption, submarine landslide, or similar disturbance.
• Volcanic eruption: The release of magma, gases, ash, and rock fragments through a vent or opening in the Earth.
• Landslide: The rapid downward movement of rock, soil, or debris under gravity.
• Flood: The temporary covering of normally dry land by water because of heavy rainfall, river overflow, storm surges, dam failure, or poor drainage.
• Flash flood: A sudden, rapidly developing flood, often caused by intense rainfall, cloudbursts, or the sudden release of water.
• Drought: A prolonged period of abnormally low rainfall that creates water shortages and affects agriculture, ecosystems, and human activities.
• Meteorological drought: Rainfall significantly below the normal level for a region and season.
• Agricultural drought: Insufficient soil moisture for crop growth.
• Cyclone: A large rotating low-pressure weather system associated with strong winds, heavy rainfall, and sometimes storm surges.
• Storm surge: An abnormal rise in sea level caused mainly by strong winds and low atmospheric pressure during a cyclone.
• Thunderstorm: A storm produced by a cumulonimbus cloud, commonly involving lightning, thunder, strong winds, and heavy rain.
• Heat wave: A period of unusually high temperatures that may cause illness, deaths, water shortages, crop damage, and stress on infrastructure.
• Cold wave: A period of unusually low temperatures that can harm human health, livestock, crops, and transport.
• Disaster management: The organised process of planning and acting before, during, and after a disaster to reduce losses and support recovery.
• Prevention: Actions intended to avoid disaster losses where possible.
• Mitigation: Measures that reduce the severity or effects of a hazard, including earthquake-resistant buildings and flood-control structures.
• Preparedness: Advance planning and arrangements that improve the ability to respond effectively.
• Response: Immediate actions during or just after a disaster, including search and rescue, evacuation, first aid, shelter, and relief.
• Recovery: The process of restoring and improving living conditions after a disaster.
• Rehabilitation: Short- and medium-term measures to restore essential services and livelihoods.
• Reconstruction: The rebuilding of houses, infrastructure, and institutions, ideally in a safer and more resilient manner.
• Early warning system: A system that detects hazards, analyses their likely effects, and communicates timely warnings so that people can take protective action.
• Community-based disaster management: Disaster planning and action involving local communities, their knowledge, resources, and participation.
• Structural measures: Physical engineering works such as embankments, shelters, retaining walls, and reinforced buildings.
• Non-structural measures: Policies, education, land-use planning, insurance, warning systems, building codes, and awareness programmes that reduce risk without major construction.

Causes and Consequences

• Natural processes create hazards, but social conditions determine whether they become disasters. Unsafe buildings, poor planning, poverty, environmental degradation, weak governance, and limited coping capacity can transform a hazard into a disaster.

• Earthquake impacts vary according to both physical and human factors. Damage is influenced by magnitude, depth of focus, distance from the epicentre, ground conditions, building quality, population density, and time of occurrence. Safety measures include seismic building codes, avoiding unstable ground, securing heavy objects, preparing emergency kits, and practising Drop, Cover, and Hold.

• Tsunamis can intensify near coasts. Tsunami waves may travel rapidly across deep ocean water but become higher and more destructive in shallow coastal areas.

• Volcanic eruptions produce several distinct hazards. These include lava flows, ash fall, poisonous gases, pyroclastic flows, lahars, and mudflows.

• Landslides result from the interaction of physical conditions and human activity. Steep slopes, intense rainfall, earthquakes, weathering, deforestation, road cutting, mining, and unplanned construction promote landslides. Land-use planning and environmental protection can reduce exposure and slope instability.

• Flooding has multiple causes and requires combined management. Intense rainfall, river overflow, cloudbursts, snowmelt, cyclones, dam failure, poor drainage, and encroachment on floodplains may produce floods. Impacts can be reduced through watershed management, afforestation, floodplain zoning, improved drainage, embankments, reservoirs, raised platforms, wetland conservation, and flood forecasting.

• Drought affects water supply, agriculture, ecosystems, and human activities. Rainwater harvesting, watershed development, efficient irrigation, drought-resistant crops, groundwater recharge, crop diversification, and careful water management reduce its impacts.

• Cyclones develop over warm ocean waters and generally weaken over land or cooler water. Their hazards include destructive winds, intense rainfall, flooding, storm surges, coastal erosion, and damage to crops, houses, roads, power systems, and communication networks. Preparedness includes accurate forecasts, timely evacuation, cyclone shelters, strong housing, protection of communication systems, and securing boats and loose objects.

• Thunderstorms and lightning create both direct and indirect risks. They can cause deaths, fires, crop damage, power failures, and disruption of transport and communication. During lightning, people should avoid open fields, isolated trees, water bodies, metal objects, and exposed high places; safe shelter is preferable.

• Heat waves are intensified by urban conditions and climate variability. Urbanisation, lack of vegetation, concrete surfaces, high humidity, and climate variability can increase heat-wave severity. Heat waves may cause illness, deaths, water shortages, crop damage, and stress on infrastructure. Cold waves similarly threaten human health, livestock, crops, and transport.

• Exposure can be reduced through land-use planning. Avoiding settlement in floodplains, unstable slopes, coastal surge zones, and other high-risk areas can substantially reduce disaster risk.

• Environmental degradation increases disaster impacts. Deforestation, wetland destruction, soil erosion, and unplanned urban growth can increase the frequency or severity of impacts. Sustainable development should protect wetlands, forests, and mangroves.

• Climate change influences some weather-related hazards but does not determine every hazard independently. It can affect the intensity, frequency, or distribution of some hazards, while natural processes and local geographical conditions remain important.

• Disaster management is a continuing process rather than only an emergency response. Its stages include prevention, mitigation, preparedness, response, recovery, rehabilitation, and reconstruction. Risk reduction is more effective and economical when integrated into development planning.

• Scientific and technological systems support, but do not replace, community action. Remote sensing, geographic information systems, satellite data, weather forecasting, seismological monitoring, and communication networks assist hazard mapping, prediction, warning, and relief operations. Warnings are effective only when they reach people in understandable form and communities know how to respond.

• Local communities are essential to disaster management. They are usually the first responders and possess knowledge of local conditions. Effective management therefore requires coordination among government agencies, local authorities, scientific institutions, emergency services, voluntary organisations, and communities.

• Disaster management must be inclusive. Poor communities, children, older people, persons with disabilities, women, and people dependent on natural resources may face greater vulnerability. They require equal access to warnings, evacuation, relief, healthcare, and recovery support.

• International policy has strengthened disaster-risk reduction. The United Nations declared the 1990s the International Decade for Natural Disaster Reduction, encouraging international cooperation. The Sendai Framework for Disaster Risk Reduction, covering 2015–2030, emphasises understanding risk, strengthening governance, investing in resilience, and improving preparedness and recovery.

What Gets Asked

• Distinguish between a natural hazard, disaster, risk, exposure, and vulnerability, and explain the relationship Disaster risk = Hazard × Exposure × Vulnerability.
• Explain why the same hazard may produce different levels of damage depending on building quality, population density, poverty, preparedness, environmental conditions, and coping capacity.
• Compare the causes, impacts, and management measures associated with earthquakes, tsunamis, volcanic eruptions, landslides, floods, droughts, cyclones, thunderstorms, heat waves, and cold waves.
• Evaluate the relative importance of structural measures, non-structural measures, early warning systems, land-use planning, environmental protection, and community-based disaster management.
• Explain why prevention and mitigation integrated into development planning are more effective than relying solely on emergency relief after a disaster.
• Assess the significance of the International Decade for Natural Disaster Reduction and the Sendai Framework for Disaster Risk Reduction (2015–2030) in promoting international cooperation and resilient development.