Hazardous environments atmospheric hazards Flashcards
Pre-Conditions for tropical cyclones.
Sea temperatures must be over 27oC to a depth of 60m for an extended period as the latent heat given off during condensation provides the energy that drives the storm
The low pressure area has to be far away enough from the equator so that Coriolis force creates rotation in the rising air mass - if it is too close to the equator there is insufficient rotation and tropical storms will not develop. The storm needs to be approximately 5-15 degrees north or south of the equator as if it is too close to the equator there will not be enough rotation so the storm will not develop.
Conditions needs to be unstable with a high humidity (elaborate)
There also needs to be weak winds active in the upper troposphere which are strong enough to transport excess heat away from the storm but not so strong to that the top of the storm system is removed (elaborate)
Only 10% tropical disturbances develop into tropical storms
Impacts of tropical storm
Tropical storm brings intense rainfall and very strong winds, which may in turn cause storm surges and coastal flooding, and other hazards such as landslides.
Tropical storm are characterised by enormous quantities of water. This is due to their origin over tropical regions. High-intensity rainfall, as as large totals - up to 500mm in 25 hours invariably cause flooding in especially low lying areas.
Their path is erratic, so it is not always possible to give more than 12 hours notice of their position. This is insufficient for effective evacuation measures.
How are tropical storms measured?
Tropical storms are the most violent, damaging and frequent hazard to impact the tropical regions. They are measured on the Saffir-Simpson Scale, which is a 1-5 rating based on the tropical storm’s intensity. It is used to give and estimate of the potential property damage and flooding expected along the coast from a tropical storm landfall.
Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf and the shape of the coastline in landfall region. Tropical storms can also cause considerable loss of life.
Factors affecting the hazards caused by tropical storms
Tropical storm paths are unpredictable, which makes the the effective management of the threat difficult.
Firstly, warmer ocean waters leads to greater evaporation and more condensation, and so more release of latent heat and higher wind speeds. Maximum wind speeds of hurricanes between 2019 and 2023 were boosted by an estimated 19mph (30km/h) on average as a result of human-driven ocean warming, according to a recent study, external. Secondly, a warmer atmosphere can hold more moisture, leading to more intense rainfall.
Strength the strongest storms do not always cause the greatest damage.
Distribution of population. The distribution of the population will depend whether the risk associated with tropical storm is increased or reduced. Places like the Caribbean islands, for e.g. where much of the population lives in coastal settlements and is exposed to increased sea levels and flooding therefore will experience far greater impacts then that of a sparsely populated in land areas.
Hazard mitigation depends on the effectiveness of human response to natural events - including urban planning laws, emergency planning, evacuation measures and relief operations such as re-housing schemes and distribution of food aid and clean water.
Inadequate planning and preparation. LICs tend to lose more lives to than inadequate planning and preparation.
What is the distribution of tropical cyclones, hurricanes and typhoon? (large-scale atmospheric disturbances)
Tropical cyclones, hurricanes, and typhoons develop as low pressure systems over warm tropical oceans.
Globally, the spatial distribution of tropical storms is not even; they occur seasonally when the conditions for their formation are optimum. About 80% of tropical storms occur around the ITCZ - the zone of where two Hadley Cells meet - which alternates between 5 and 15 degrees north and south of the equator.
About 50% of all storms occur in the Pacific Ocean with most developing off the coast of Japan.
Other significant areas of formation include the seas surrounding Australia ( about 20%) and the Caribbean (about 11%).
Tropical storm also vary temporally; the Atlantic Hurricane season is from 1 June to 30 November and 97% of hurricane occur between these dates.
What is the distribution of tornadoes?
Whilst tornadoes have been observed in every continent, with the exception of Antarctica, they tend to be found in mid-latitude regions given that their formation is dependent upon the interaction of contrasting air masses. (elaborate)
Around 80% of all recorded tornadoes occurs in the USA with the Great Plain (Oklahoma, Texas and Kansas) having the highest global frequency of over five tornadoes per year, being named Tornado Alley.
Explain the formation of a large-scale atmospheric disturbance.
Warm, moist air rises, leaving an area of low pressure below. This causes warm air in surrounding areas of higher pressure to move into this low pressure areas and rise too. Overall, warm air is constantly rising accumulating into the atmosphere.
When the warm air rises, it cools, condensing into thunderstorm clouds.
The whole system spinning due to the Coriolis effect.
The constant addition of energy from the warm air causes the storm to spin faster and generate higher wind speeds. At 39mpg the storm can be classed as a tropical storm.
The eye of the storm is in the centre. This is an area that is around 30 miles wide and it is an areas of extremely low pressure. Cool, dry air from higher altitudes descends into the eye, causing the weather to in the eye to be relatively calm and cloud free.
Surrounding the eye is the eyewall, the most intense and powerful area of the storm, Warm, moist air rapidly rises here, with extremely high winds and torrential rain. When winds reach 74mph, it becomes a hurricane/cyclone/typhoon.
How do hurricanes “die” over land?
Hurricanes require warm ocean water, typically above 27oC to sustain their strength via latent heat. With less evaporation occurring over land, there’s a decrease in moisture available, disrupting the storm’s circulation. Furthermore, the rough terrain of land creates more friction which reduces the hurricane’s surface circulation and weakening its overall structure.
Why do hurricanes take particular directions?
In the tropic, where hurricanes for, easterly winds known as trade winds steer a hurricane towards the west. In the Atlantic ocean, storms are carried by these trade winds from the west coast of Africa, westward towards the Caribbean Sea and the North American coasts.
Due to the clockwise rotation of air in the northern hemisphere of air associated with high pressure systems often cause hurricanes often cause hurricanes to stray from their initially east-to-west movement and curve northward.
Explain the formation of a tornado.
The sun heats the grounds, warming the surface and stimulating convection..
Warm air rises, cools and condenses to form shallow cumulus clouds. If the atmosphere is unstable, this warm air will continue to rise to greater heights, thereby creating a taller cumulonimbus cloud.
Where this occurs in environment where wind speed increases strongly with height, the higher fast moving air can begin to spin over the slower air below, creating a horizontal wind that spins and rolling like a cylinder.
Powerful warm updraughts tilt the cylinder vertically, creating of column of spinning winds.
Thunderstorms that have persistent and rotating updraughts (supercells).
Falling downdraughts of cold air within the supercell bring the column of spinning winds downwards. If this column of air reaches the ground a tornado is formed.
Explain the hazard of storm surges (large scale atmospheric disturbances)
The majority of deaths (over 90%) resulting from tropical storm are caused by storm surges. As storm surge hit land low-lying coastal areas are particularly vulnerable to the waves driven by the strong winds of hurricanes. For example, Hurricane Katrin in 2005 was a category 5 storm with winds up to 280km/h. Theses strong winds pushed waves towards the south eastern coastline in U.S., causing water to “pile up”. Consequently, resulted in a storm surge with waves over 8m high, destroying 80% of New Orleans in Louisiana. The surge was responsible for the deaths of over 1800 people. Furthermore, the influx of seawater can cause extensive salt water contamination, this reduce soil fertility, leading to a reduction in agricultural productivity.
How can you evaluate the impacts of a storm surge?
(Good points for eval)
The impact of storm surge depends on the topography of the coast, the wind strength and the height of the tide, land use, population density, vulnerability and preparedness.
(elaborate)
Explain how heavy rainfall is a hazard?
(large-scale atmospheric disturbances)
Heavy rainfall leads to more water infiltrating the soil. This increases the pore water pressure of the soil, reducing the slope’s internal strength. Heavy rainfall will lead to the soil becoming saturated, causing the cohesive bonds between soil particles to break. Consequently, lead to mass movement as the slopes moves similar to that of a viscous liquid. For instance, in 2017, Hurricane Maria caused of 40,000 landslides in Puerto Rico, damaging infrastructure such as roads and isolating communities from emergency services.
Additionally, as mentioned previously, heavy rainfall causes the soil to become saturated. This leads to overland flow, increasing the rate at which water enters the river. As a result, the increases the risk of river flooding.
Large areas of standing water coupled with warm tropical climate can result in water-borne diseases that can induce epidemics long after the storm has passed. However, heavy rainfall from storm can sometimes bring much-needed precipitation to arid regions, leading to the irrigation of crops as well as an increase in water security. For example, Japan receives over half of its precipitation from typhoon events.
Explain how strong winds are a hazards?
(Small scale and large scale disturbances)
Winds from tropical storms and cyclones can reach 320km and cause structural damage to buildings and infrastructure.
Loose debris can become lethal projectiles.
Strong winds can also destroy power lines, hampering communication and disrupting rescue efforts. Due to Hurricane Helene in 2024, over a million customers lost electric power in the state of Georgia as the strong winds caused trees to fall on power lines. In parallel, the state had agricultural damage of $6.36 billion as strong winds as crops were defoliated, snapped or uprooted by strong winds.
The 2011 Hackleburg-Phil Campbell tornado was an EF5 tornado. According to the American Red Cross, 70% of Hackleburg was destroyed with trees uprooted and cars thrown hundreds of yards.
Explain how pressure differences are a hazard (small scale hazards)
The air pressure inside a tornado can be as much as 10% lower compared to the surrounding air. This creates a significant pressure difference between the inside and outside of buildings. As a higher pressure always moves to lower pressure, roofs are lifted of buildings.
Explain how HICs struggle with the management of large-scale atmospheric disturbances.
In 2012 Hurricane sandy led to 24 states being directly affected and people killed were in 9 states, including New York (49 deaths), New Jersey (10 deaths) and Connecticut (3 deaths). Two days after the storm hit, the widespread destruction of electricity grid led to 6 million customers without electricity, highlighting the fragility of the ageing American electricity network.
Explain how large scale atmospheric disturbances are monitored.
The National Hurricane Centre in Miami, Florida uses geostationary satellites and ground-based recording stations to observe developing storms. The data is then fed into computer models based on previous events and hurricane paths to estimate the likely track and intensity of the storm event. The track of the hurricane is difficult to predict, however it is vital that data is interpreted accurately for warning to be given and for lives to be saved.
Satellite and radar data and automated land and sea surface observations can be used to generate storm imagery using computer graphics.
Developing hurricanes with well-formed eyes can be located out to sea within 30-50km. When a hurricane is about 250kn offshore, weather radar enables the position of the hurricane to be constrained within about 10km.
Continuous real-time monitoring enables forecasting and warning in a similar way to weather monitoring and forecasting.
What are the issues of monitoring large-scale atmospheric disturbances?
The track of the hurricane is difficult to predict, however it is vital that data is interpreted accurately for warning to be given and for lives to be saved.
Too many wrong warning can induce complacency in the population and causes massive economic losses as people are evacuated unnecessarily.
Why is the issues of evacuating communities from large scale atmospheric disturbances?
Evacuation of communities at risk has become more time consuming and complex as population densities around coastal areas have increase. For example, it took 24 hours for 1 million people to be evacuated before Hurricane Katrina hit the city of New Orleans.
How are tornadoes predicted?
Radar and satellite technology are used to monitor atmospheric conditions although its is not possible to accurately predict the tornado’s location, path or intensity. However, using these technologies have resulted in the number of false warning from tornadoes falling from 73% to 24%.
The US National Severe Storms Laboratory (NSSL) uses data from weather balloons, satellites, aircraft and surface weather stations to calculate atmospheric conditions and issue warnings. Areas of the USA that frequently receive tornadoes such as the Oklahoma and Kansas, have reduced the death rate due to these warning and subsequent responses to the hazard.
Explain how perception of risk influences the effects of hazards.
People who have not experienced the hazards are not usually willing to take the necessary actions to avoid it. In 1992, when Hurricane Andrew threated southern Florida, the authorities decided to evacuate people from coastal areas likely to be affected. The decision was difficult because the economy is harmed by stopping normal, so the authorities who make the decision to evacuate are strongly criticised in the disaster does not occur. Hurricane Andrew caused 15 deaths amongst citizens who refused to evacuate because they had never known a Hurricane as far inland as Andrew reached. In contrast, individuals who have experienced natural disasters tend to have heightened risk perceptions.
Social and cultural influences: Countries such as China, Japan and South Korea Many Asian cultures tend to be collectivist, meaning that there are stronger social networks with shared experiences of past natural hazards. In some cultures such as Aboriginal communities in Australia, strong emotional and historical ties to land can influence decisions about staying in high risk areas.
Explain how income effects vulnerability to a hazard?
For the poorest in society, accessing basic necessities may be a greater cause for concern compared to the potential risk of natural hazards. Additionally, the poorest may have low quality education and may be therefore completely unaware that they are living in a dangerous location. In contrast, the rich have access to private mobility and can afford to move quickly out of danger and can afford to regain a normal life more rapidly after the hazard life.
Explain how age effects vulnerability to a hazard?
In Japan, 35% of the population older than 65. The elderly are weaker and are less able to migrate or withstand the effects of a hazard on their health.
Explain how water can cause mass movement.
If too much water infiltrates into the soil, this will increase pore water pressure, reducing friction between soil particles. The internal strength is thus reduced and the material become unstable as cohesive bonds between soil particles become weaker. Consequently, this results in liquefaction, causing flows to occur.
Explain how tectonic factors can cause mass movement.
The mountain building process occurring at convergent margins (collisional and destructive) can create the high and steep relief on which slope failure is more likely to occur, and such areas are found in both humid and arid tropics.
As the slope becomes steeper, the proportion of the gravitational force acting parallel to the slope (shear force) increases, thereby increasing the shear stress and increasing the risk of mass movement.
The presence of volcanic activity at destructive and constructive margins as well as hot spots at intra-plate locations also produces steep slopes, which are often have unconsolidated volcanic ash and lapilli. If this material combines with intense rain or glacial meltwater from subglacial high altitude eruption, then lahars can form and travel rapidly.
When an earthquake occurs, shock waves radiate outwards from the epicentre in all directions, causing ground shaking which increases shear stress on the slope.
(mass movement doc)
Explain how human factors increase the risk of mass movement.
Humans can increase the likelihood of mass
movement occurring through construction of buildings
and infrastructure - this may be by cutting or excavating
land, which can remove underlying support previously
given to slopes, thus reducing (shear strength), or by the
constructions adding weight and pressure to the ground
(building on slopes adds weight, increasing shear stress).
Humans may also play a part in determining vegetation
cover by cutting down and removing trees and changing
the dominant vegetation type in an area, or allowing
overgrazing to take place in an area, reducing the shear
strength of slopes.
Mention how as population are growing much throughout the tropics, land use is extending to increasingly marginal areas.
Causes of avalanches
Management of slope hazards.
How do warning work for hurricanes?
A hurricane watch is issued for a specific coastal area for which a hurricane or hurricane-related hazard is a possible threat within 36 hours. A hurricane warning is issued when a severe storm with sustained winds of 74 mph or higher is expected in a specified coastal area in 24 hours or less.
A hurricane warning can remain in effect when dangerously high water or exceptionally high waves continue, even though the winds may have subsided below hurricane intensity.
Medium sized cities need about 12 hours to evacuate and larger cities
need at least 72 hours, so evacuation warnings advising people at risk are issued alongside forecasts.
