Natural hazards come in various forms, from earthquakes to hurricanes. They're classified as geological, hydro-meteorological, or biological, each with unique characteristics and potential secondary effects. Understanding these types helps us prepare for and mitigate their impacts.

The causes of natural hazards are complex, involving geological, meteorological, and hydrological processes. Human activities like deforestation and urbanization can worsen their effects. Climate change is also altering the frequency and intensity of many hazards, making them more unpredictable.

Natural hazard classification

Types of natural hazards

• Geological hazards originate from internal earth processes (plate tectonics, seismic activity, volcanic eruptions)
  • Earthquakes occur when stored elastic strain energy is suddenly released along a fault plane, causing seismic waves that shake the ground
  • Tsunamis are generated by the displacement of a large volume of water, typically due to earthquakes, submarine landslides, or volcanic eruptions in oceanic regions
  • Volcanic eruptions happen when magma rises through the Earth's crust and is expelled onto the surface, often accompanied by ash, gases, and lava flows
  • Landslides involve the downslope movement of soil, rock, or debris, triggered by factors such as heavy rainfall, earthquakes, or human activities that destabilize slopes
• Hydro-meteorological hazards are caused by atmospheric, hydrological, or oceanographic processes
  • Tropical cyclones (hurricanes, typhoons) form over warm ocean waters and are characterized by low-pressure centers, strong winds, and heavy rainfall
  • Floods occur when water overflows onto normally dry land, often due to heavy rainfall, rapid snowmelt, or the failure of man-made structures (dams, levees)
  • Droughts are prolonged periods of low precipitation leading to water scarcity and increased wildfire risk
  • Heatwaves are extended periods of excessively hot weather that can cause heat-related health impacts
  • Storm surges are abnormal rises in sea level generated by strong winds and low atmospheric pressure during storms, which can cause coastal flooding
• Biological hazards are caused by exposure to living organisms and their toxic substances or vector-borne diseases
  • Epidemics are widespread occurrences of an infectious disease in a community at a particular time
  • Pandemics are epidemics that spread over multiple countries or continents
  • Insect or animal plagues are outbreaks of pests or diseases that can damage crops, livestock, or human health (locusts, rodents)

Hazard characteristics and secondary effects

• Natural hazards can be classified based on their frequency, duration, and area of extent
  • Rapid-onset hazards occur suddenly with little warning (earthquakes, flash floods, tornadoes)
  • Slow-onset hazards develop gradually over an extended period (droughts, sea-level rise)
• Some natural hazards can trigger secondary hazards, creating a cascade of impacts
  • Earthquakes can cause landslides, tsunamis, or damage to infrastructure leading to technological hazards (dam failures, chemical spills)
  • Hurricanes can cause flooding, storm surges, and tornadoes, leading to extensive damage and loss of life
  • Volcanic eruptions can trigger lahars (volcanic mudflows), wildfires, or create ash clouds that disrupt air travel and cause respiratory issues

Processes behind natural hazards

Geological processes

• Plate tectonics involve the movement and interaction of Earth's lithospheric plates, leading to geological hazards
  • Convergent plate boundaries, where plates collide, can cause earthquakes, volcanic eruptions, and mountain building
  • Divergent plate boundaries, where plates pull apart, can create rift valleys, submarine ridges, and volcanic activity
  • Transform plate boundaries, where plates slide past each other, are characterized by shallow earthquakes and offset landforms (San Andreas Fault)
• Seismic activity is the result of sudden movements within the Earth's crust or along plate boundaries
  • Elastic strain energy accumulates in rocks due to tectonic forces and is released suddenly during an earthquake
  • The focus is the point within the Earth where an earthquake originates, while the epicenter is the point on the surface directly above the focus
  • Seismic waves radiate outward from the focus, causing ground shaking and potential damage to structures

Meteorological and hydrological processes

• Meteorological processes in the atmosphere, such as air pressure differences, wind patterns, and moisture content, can lead to various weather-related hazards
  • Tropical cyclones form when warm, moist air rises over warm ocean waters, creating a low-pressure system that draws in more air and generates strong winds
  • Severe thunderstorms develop when unstable atmospheric conditions allow warm, moist air to rise rapidly, leading to the formation of tall cumulonimbus clouds
  • Jet streams, fast-moving air currents in the upper atmosphere, can influence the path and intensity of weather systems
• Hydrological processes involve the movement and distribution of water on Earth's surface and can contribute to hazards
  • The water cycle describes the continuous movement of water through evaporation, transpiration, condensation, precipitation, and runoff
  • Soil moisture and groundwater levels can influence the occurrence and severity of floods and droughts
  • Snowmelt in mountainous regions can contribute to spring flooding and alter the timing and magnitude of peak river flows

Human impact on hazards

Land-use changes and infrastructure development

• Human activities can exacerbate the frequency and intensity of some natural hazards by altering the natural environment and increasing vulnerability
  • Deforestation reduces the capacity of vegetation to intercept rainfall and stabilize slopes, increasing the likelihood of landslides and flash floods
  • Urbanization can increase the area of impervious surfaces (roads, buildings), leading to higher surface runoff and increased flood risk in cities
  • Agricultural practices, such as overgrazing or monocropping, can degrade soil quality and increase erosion, making land more susceptible to hazards
• The construction of infrastructure can provide protection against some hazards but may also create new risks
  • Dams and levees can regulate river flow and prevent flooding, but their failure can lead to catastrophic floods downstream
  • Coastal defenses (seawalls, breakwaters) can protect against storm surges and erosion, but may also alter sediment transport and beach dynamics
  • Buildings and bridges designed without proper hazard-resistant features can collapse during earthquakes or strong winds

Population growth and vulnerability

• Population growth and migration can increase the number of people exposed to natural hazards
  • Coastal areas are attractive for settlement and tourism but are exposed to hazards like hurricanes, tsunamis, and sea-level rise
  • Floodplains provide fertile soil for agriculture but are prone to river flooding
  • Seismically active regions near plate boundaries are often densely populated (Japan, California), putting many people at risk from earthquakes
• Inadequate land-use planning, building codes, and risk reduction measures can increase the vulnerability of communities to the impacts of natural hazards
  • Informal settlements and substandard housing are more likely to suffer damage during hazard events
  • Lack of early warning systems and evacuation plans can hinder timely response and lead to higher casualties
  • Limited access to resources and services (healthcare, insurance) can make it harder for communities to recover from disasters

Climate change and hazards

Impacts on hydro-meteorological hazards

• Climate change is expected to alter the frequency, intensity, and distribution of various natural hazards, particularly those related to hydro-meteorological processes
  • Rising global temperatures are likely to increase the frequency and severity of heatwaves and droughts, leading to increased water scarcity, wildfire risk, and heat-related health impacts
  • Changes in precipitation patterns, such as more frequent and intense extreme rainfall events, can increase the risk of flooding and landslides in some regions
  • Sea-level rise, resulting from thermal expansion of the oceans and melting of land-based ice, can increase the risk of coastal flooding, storm surges, and coastal erosion, particularly in low-lying areas and small island states
• The impacts of climate change on tropical cyclones remain uncertain and may vary regionally
  • Warmer ocean temperatures may increase the intensity of tropical cyclones, but changes in atmospheric circulation patterns could also influence their frequency and tracks
  • Rising sea levels can exacerbate storm surge heights and coastal flooding during cyclones

Indirect effects on geological hazards

• Climate change may have indirect effects on geological hazards through various mechanisms
  • Increased frequency and intensity of rainfall events can raise the risk of landslides by saturating soils and destabilizing slopes
  • Melting of glaciers and permafrost in high-altitude and high-latitude regions can increase the risk of glacial lake outburst floods and landslides as previously frozen ground thaws and weakens
  • Changes in the distribution of water and ice mass on Earth's surface due to melting glaciers and ice sheets may alter the stress patterns in the Earth's crust, potentially influencing earthquake frequency or volcanic activity, although these effects are not yet well understood
• The impacts of climate change on natural hazards will vary regionally and will interact with other factors such as population growth, urbanization, and land-use changes
  • Adaptive risk reduction strategies, such as improved land-use planning, hazard-resistant infrastructure, and early warning systems, will be necessary to build resilience to the changing hazard landscape
  • International cooperation and support will be crucial to help vulnerable communities and developing nations cope with the increasing impacts of climate change on natural hazards