ThinkHazard! provides information about 10 hazard phenomena triggered by Earth geophysical, hydrologic and meteorologic processes.
Geophysical hazards¶
These processes originates from within the Earth. They are not much influenced by climate variables or human actions, and typically the range of their return period spans over many centuries.
Earthquake
Earthquakes are the result of forces deep within the earth’s interior. When they reach the surface, the vibration of the ground can cause the collapse of buildings and destruction of life and property. Earthquakes are difficult to predict and can have devastating effects. Earthquakes usually happens along a fault plate, the border between tectonic plates. Earthquakes often trigger landslides, tidal waves and tsunamis. Powerful aftershocks frequently occur, causing further damage and increasing psychological stress.
Tsunami
A tsunami is a series of waves caused by a rapid displacement of a body of water (ocean, lake). The waves are characterised by a very long wavelength and their amplitude is much smaller offshore. The impact in coastal areas can be very destructive as the waves advance inland and can extend over thousands of kilometers. Tsunamis are triggered by be earthquakes and volcanic eruptions.
Volcanic eruption
Volcanic eruptions happen when lava, gas and ashes are discharged from a volcanic vent. This can trigger different type of hazards to life and property, including lava flows, lahars, ash falls, debris avalanches, and pyroclastic density currents. Ash plumes originated from volcanic eruptions can spread on large areas, causing disruption of air traffic.
Hydraulic hazards¶
A hazard caused by the occurrence, movement, and distribution of surface and subsurface freshwater and saltwater. These hazards are tied to the water cycle, and thus can be affected by human activities and meteoclimatic processes.
Floods (pluvial and fluvial)
Flood hazard includes two similar phenomena:
Fluvial (or riverine) floods occur when intense precipitation over an extended period of time causes a river to exceed its capacity, triggering the overflow or breaching of river embankments and ultimately causing the submersion of natural and human soil in the floodplains. Fluvial floods can also happen due to heavy snow melt and ice jams. Floods onset time and intensity can vary greatly due to geomorphological and climatic conditions, from very slow to extremely fast and intense (flash floods).
Pluvial (or surface water) floods are also a consequence of heavy rainfall, but they happen outside of a water body, such in an urban area. Pluvial floods can be triggered by the saturation of the urban drainage system, causing water to flow out into the streets; or they can happen due to the fast rainfall run-off from hillsides areas when degraded soil and lack of natural vegetation reduce the absorbing capacity of soil. Hillsides hit by wildfires, for example, can be sources of pluvial floods.
Landslides
A landslide is the movement of natural soil and rocks controlled by gravity. Landslides can involve dry mass or wet mass. Dry mass movements can be triggered by violent geophysical hazards such as earthquakes and volcanic eruptions, but they can also be a consequence of water scarcity and soil erosion. Diffeerently, wet mass movements (mudslides) are more often caused by heavy precipitation or ice melting. Landslides are associated with other hazards such as floods, tropical cyclones, and severe local storms.
Coastal floods
Coastal floods can be triggered by violent storm surge events or happen due to extreme tidal events; both pheonomena are made more severe by sea leve rise. A tidal wave/storm surge is the rise of the water level in a water body (the sea, an estuary or lake) as result of strong wind driving water towards the coast. This so-called wind setup is superimposed on the normal astronomical tide. The mean high water level can be exceeded by five and more metres, triggering coastal flooding. Storm surges are associated with tropical cyclones, strong winds, and tsunamis.
Meteo-Climatological hazards¶
A hazard caused by extreme weather and atmospheric conditions. Meteorological hazards range from hours to days, and influence the micro- to meso- scale. Climatological hazards are meso- to macro-scale processes ranging from intra-seasonal to multi-decadal climate variability. Human-induced global warming has a strong effect on the frequency and magnitude of such hazards.
Cyclonic Strong Winds
Cyclones, tropical storms, hurricanes and typhoons, although named differently, describe the same type of hazard: a non-frontal storm system that is characterised by a low pressure center, spiral rain bands and strong winds. Usually it originates over tropical or subtropical waters and rotates clockwise in the southern hemisphere and counter-clockwise in the northern hemisphere. The system is fueled by heat released when moist air rises and the water vapor condenses. The onset is extensive and often very destructive. Tropical cyclones can generate strong winds, floodings and storm surges.
Water scarcity
Water scarcity, or drought, is defined as a deficiency of rainfall over an extended period – a season, a year or several years – relative to the statistical multi-year average for the region. Lack of rainfall leads to inadequate water supply for the environments and human activities. A drought may trigger other natural hazards such as wildfires, extreme temperatures, desertification, famine and epidemics.
Extreme temperatures
A heat wave is a prolonged period of excessively hot and humid weather compared to the normal climate patterns of a region. Asphalt and concrete store heat and gradually release heat at night, resulting in the “urban heat island effect.” Consequently, people living in urban areas may be at greater risk from the effects of a prolonged heat wave than those living in rural areas.
A cold wave can be both a prolonged period of excessively cold weather and the sudden invasion of very cold air over a large area. It can cause damage to agriculture, infrastructure and property.
Wildfires
Wildfire and urban fires describes an uncontrolled burning fire, usually originated in natural areas, which can cause damage to forestry, agriculture, infrastructure and buildings. Naturally-occuring wildfires are triggered by extreme heat and drought conditions, but also by lightning storms.