Storm Hazards Flashcards
The nature of tropical storms
They are huge spinning storms with tropical winds and torrential rain.
They require warm water (27 degrees to a depth of at least 70 metres).
As warm, moist air rises, it releases energy that increases wind speed.
Conditions needed for tropical storms to form
A disturbance, such as an area of low pressure that triggers the storm
A convergence of air in the lower atmosphere - either within the inter-tropical convergence zone or along the boundary between warm and cool air masses. This forces warm air to rise.
How tropical storms form
They form in the tropics and move westwards due to easterly winds.
They occur at least 5 degrees from the equator.
They cannot form any closer because the coriolos effect isn’t strong enough to make them spin.
They also move away from the equator because of this
They lose strength as they move over land because their supply of warm, moist air is cut off.
The Coriolos effect
The rotation of the earth which deflects objects and air (to the right in the northern hemisphere) along the earths surface.
Latent heat
The energy that is the driver of tropical storms, while the presence of moisture allows low frictional drag with the surface of the ocean.
Circular storms
There is a low pressure point at the centre, called the eye.
In the eye wall there are rising air spirals that cause strong winds.
Near the top of the storm, there is an outflow of moisture - laden air so cloud cover extends for a long distance either side of the eye.
Measuring storms
Storm magnitude is measured in the Saffir-Simpson scale.
It measures wind speed from 1 (weakest winds of 120-150kmh) to 5 (strongest winds of over 250kmh)
It also measures damage done from 1 (limited) to 5 (catastrophic)
Frequency
Tropical storms are quite frequent with around 100 occurring each year.
Some never reach land so don’t develop into hazards.
Predictability
Storms are more frequent in the Northern hemisphere between June and November, and the Southern Hemisphere between November and April.
They can be predicted using satellite imagery to identify cloud formations.
The storm can then be predicted using satellite imagery and models, helping scientists to work out when it will hit.
Predictions are usually accurate however storms are largely irregular due to the number of factors affecting when one will form.
Winds
Wind speeds on the ground can reach more than 300km/h.
They can destroy buildings, uproot trees and carry debris long distances before smashing them into other objects.
Storm surges
A large rise in sea level caused by high winds pushing water towards the coast, and by the low pressure of the storm.
They account for around 90% of tropical storm deaths.
Waves can reach 10m high if a surge coincides with high tide, devastating coastal communities by destroying buildings, roads and contaminating agricultural land with salt from sea water.
Heavy rain
Warm moist air rises, cools, condenses and then falls as torrential rain. This can lead to secondary hazards such as flooding and landslides. During tropical storms, there tends to be around 100mm of rainfall a day.
E.g. Storm Denise 1966, over 1000mm of rain fell in 12 hours
Standing water + warm temperatures = breeding ground for mosquitos, leading to malaria.
Flooding
Heavy down pours cause river discharge to increase suddenly, causing rivers to overtop their banks and flood the surrounding area.
Heaving rain and storm surges can also cause flooding in coastal areas.
Landslides
Water infiltrates soil and rock, adding weight and making it less stable, increasing the risk of landslides.
Social impacts
People may drown, be injured or killed by debris that’s blown around or carried by water.
People left homeless
Electricity cables damaged, so supplies are cut off
Flooding = sewage overflow = contaminated water = disease
Food shortages due to damage to agricultural land
Economic impacts
Buildings and infrastructure cost a huge amount to rebuild
Businesses are destroyed, so they can’t trade
Commercial farming suffers as agricultural land is damaged
Environmental impacts
Beaches are eroded and coastal habitats are damaged (e.g. Coral reefs)
Fish breeding grounds could be damaged by sediment
Landslides can block water courses so they change course.
Political impacts
People may blame authorities for a lack of food, water and energy, leading to political unrest.
Repairs are expensive so the development of the country will be limited.
Social impacts - Katrina
1836 people died
300,000 homes destroyed, many homeless and 3 million without electricity
Parts of the 1-10 bridge collapsed, blocking one of the main routes out of New Orleans.
Water supplies were polluted with sewage- 5 died from contaminated water.
18 schools destroyed and 74 badly damaged
Economic impacts - Katrina
Largest impact
230,000 jobs lost
Industry disrupted - 30 oil platforms in the Gulf of Mexico were damaged or destroyed, ports such as Gulfport in Mississippi was damaged.
5300km^2 of forest was destroyed in Mississippi, causing around $5 billion lost income from logging
Total cost of damage was around $300 billion
Environmental impacts - Katrina
Coastal habitats such as sea turtle breeding beaches were damaged.
Coastal conservation areas such as Breton National Wildlife refuge in Lousiana were destroyed.
Flooding to oil refineries in Louisiana caused spills
Flooding of salt marshes lead to habitat loss
80% of New Orleans was flooded.
Economic impacts - cyclone nargis
6000km^2 of agricultural land was damaged, including rice paddies.
40% of food stores were destroyed
Fishing boats were destroyed, meaning millions of people loss their livelihood.
The total cost of damage was around US $4billion
Social impacts - Nargis
140,000 people killed
2.5 million left without shelter
450,000 homes destroyed
75% of health facilities destroyed
43% of fresh water ponds, a valuable source of water for local people were damaged by salt water.
70% of people had no access to clean water
Environmental impacts - Nargis
380km^2 of mangrove forests were destroyed
Flooding caused erosion and salinisation of the land
14,000km^2 of land was flooded.
Hurricane Katrina - Key facts
Hit the south east USA on the 29th of August 2005.
It moved North west and strengthened as it passed over the warm water of the Gulf of Mexico.
It brought winds of around 200kmh and 200-250mm of rainfall to Louisiana, and a storm surge of up to 8.5m to Mississippi
Cyclone Nargis - Key facts
It hit Myanmar on the 2nd of May 2008.
It was category 4 as it reached the coast.
It hit with wind speeds of 215kmh and a storm surge of 5m.
Prevention
Future development plans can avoid high risk areas.
Preparedness
Emergency services can train and prepare for disasters.
Governments can educate people (stockpiling water and food and boarding up windows)
Adaptation
Buildings are made up from reinforced concrete or by fixing roofs securely.
They can be built on stilts so that they are above flood water
Flood defences can be built along rivers (levees) and coasts (sea walls)
Responses to Katrina - Before
On the 26/08/05 the National Huricane Centre issued a hurricane warning, meaning preparations could begin.
The US coast guard positioned helicopters and boats in high risk areas.
The federal emergency management agency organised teams and supplies.
New Orleans ordered mandatory evacuation - 80% were evacuated before the hurricane reached land.
Responses to Katrina - After
The Louisiana superdome in NO sheltered 26,000 people
50,000 were rescued
$5 billion pounds in charity donations was collected.
Responses to Nargis - Before
No dedicated cyclone monitoring centre
Indian weather agencies warned Myanmars government 48 hours before the storm hit.
Myanmars weather forecasters issued warnings via TV and radio but didn’t say how severe it was going to be or give any advice on how to prepare.
There was no emergency preparation or evacuation plans.
Responses to Nargis - After
The government initially refused to accept foreign aid.
On the 9th of May they decide to accept aid donations such a food and tents.
The UN refugee agency sent shelters, water purification tablets and blankets.
Aid workers weren’t allowed into the country until the 19th of May
Military ruled Myanmar and seized and turned away some aid.
