1c - Tropical Storms Flashcards
What are Tropical Cyclones?
Tropical cyclones are intense low pressure weather systems with heavy rain and strong winds that spiral around the centre
Include: hurricanes, cyclones, typhoons - all same, just different location
What is needed for tropical cyclones to form?
- sea temp of 27 degrees or higher
- low wind shear in the upper atmosphere
- source location in the tropics (8-20 degrees N/S of equator)
- westerly trade winds
How do tropical cyclones form?
- Warm surface water evaporates, rises and condenses, releasing lots of energy powering the storm
- The rising air drawn up quickly ,creating an area of low pressure, which condense to produce cumulonimbus clouds
- Due to Coriolis force (winds moving in specific direction due to Earth’s axis) the storm spins
- When rising air reaches top of cyclone, air flows away from the centre and descends forming the eye wall
- As the storm moves over the ocean, energy from warm water strengthens storm, so increased windspeed
- Storm loses its strength when moving over land/cool water due to energy supply being cut off causing it to dissipate
What is the structure of tropical cyclones?
- alternating bands of rising and sinking air around a central eye
- rapidly rising air forms cumulonimbus clouds and rainfall
- eye has low pressure, light winds, no cloud or rain, high temp
- eye surrounded by eyewall, where there’s spiralling rising air, very strong winds, storm clouds, torrential rain, low temps
- spins anticlockwise in northern hemisphere and clockwise in southern
How are tropical storms measured?
- using the Saffir-Simpson scale
- based only on the measured, sustained wind speed
How do tropical cyclones intensify and dissipate?
Tropical cyclones intensify when water temperatures are warm, there is a low wind shear and high humidity
Tropical cyclones dissipate when they reach land so lose energy, move into colder waters and run into other weather systems where winds are blowing in different direction
The energy source is warm water of ocean temps above 27 degrees & overland cyclones are cut off from this
What physical hazards do tropical cyclones cause?
High winds
Intense rainfall
Storm surges - a large rise in sea level caused by low pressure, high winds
Coastal flooding - caused by storm surges and strong winds driving large waves onto shore
Landslides - heavy rain makes hills unstable causing landslides
What are the impacts of tropical cyclones on people?
- drowning in currents created by floodwater, storm surges
- wind speeds can destroy buildings, homelessness
- high winds and floodwater can carry debris which kills/injures people
- electricity supplies cut off because cables damaged by flood water
- flooding causes sewage overthrow, contaminating water supplies making it easier for disease to spread
- shortage of food as crops damaged and livestock killed
- damaged roads makes it difficult for aid & emergency vehicles to get through
What impacts do tropical cyclones have on the environment?
- trees uprooted by high winds which can damage/destroy wooded habitats
- storm surges can erode beaches and damage coastal habitats
- flooding can damage industrial buildings on the coast causing harmful chemicals to leak into the environment
- landslides deposit sediment in rivers and lakes which can kill fish/wildlife
Why are some countries more physically vulnerable than others to the impacts of tropical cyclones?
- low lying coastlines are vulnerable to storm surge flooding caused by low air pressure within cyclones, as well as large waves driven onshore by intense winds
- areas in the path of the tropical cyclones are hit more frequently
- steep hillsides may increase the risk of landslides
Why are some countries more socially vulnerable than others to the impacts of tropical cyclones?
Poorer countries are often more socially vulnerable as:
- health care is poor so they struggle to treat all casualties
- there is less money for flood defences/ training emergency teams
- its hard to rescue people due to poor infrastructure
- often higher pop. density in low quality buildings which are easily damaged
Why are some countries more economically vulnerable than others to the impacts of tropical cyclones?
Poorer countries are more economically vulnerable:
- people may not have insurance to cover cost of repairing damages
- many people depend on agriculture which is often badly affected leading to a loss of livelihoods
Economic impact is often greater in richer countries as the buildings/infrastructure is worth a lot more
How can countries predict tropical cyclones?
Weather forecasting - to predict its track and estimate likely storm surge heights and rainfall levels
Satellite technology - can be used to spot and track cloud formation
How can countries prepare for tropical cyclones?
ST: Warning and evacuation strategies - alerts people, giving them time to leave their home & govs can plan evacuation routes
Setting up shelters, emergency hospitals
LT: Flood defences - sea walls & levees could protect against storm surges
Education - residents know about dangers and how to respond
What is the flood risk equation?
Flood risk = hazard event x vulnerability / capacity to cope
What were the forecasting and satellite technology for Hurricane Katrina, USA
- National Hurricane Center issues forecasts using satellite images and planes that collect weather data on approaching storms - over 20 satellites operate every day
- Katrina was identified as a potential threat several days before landfall, with warnings issued as it intensified over the Gulf of Mexico.
What were the warning and evacuation systems for Hurricane Katrina
- Towns and cities such as Forty Myers are classified into risk zones based on risks from high winds or storm surges
- NHC issued hurricane warning 6 days prior landfall as Mississippi and Louisiana were declared states of emergency
- 70-80% of New Orlean residents were evacuated before hurricane reached land - some delayed evacuations of elderly, homeless and prisoners abandoned by evacuating guards - this evacuation order was not passed until less than 24hrs before landfall
- Superdome shelter used as emergency shelter but overcrowded (designed to accommodate 800ppl but 20,000 arrived) , lacking supplies
What were the defences for Hurricane Katrina
- Flood defences such as flood barriers & levées were there
- However these failed, over 50 breaches - inadequate for this magnitude
- Many of the deaths caused when a 4m high storm surge flooded 80% of New Orleans
- This is because of government spending cuts leaving levées poorly maintained
- Pumping stations flooded and failed to work
What were the environmental impacts of Hurricane Katrina
- Flooding damaged oil refineries in Louisiana causing massive oil spills - over 7 million gallons of oil leaked into water sources
- 80% of New Orleans submerged
- Coastal habitats such as sea turtle breeding beaches damaged
- Some coastal conservation areas destroyed eg about half of Breton National Wildlife Refuge
What were the social impacts of Hurricane Katrina
- Over 1800 deaths - mostly vulnerable elderly and African-Americans due to flooding in low-lying areas where low-income people were
- 300,000 destroyed houses with over a million displaced
- Damaged roads, collapsed bridges
- Overcrowding in shelters eg Superdome led to unsanitary conditions
- Waterborne diseases spread due to contaminated floodwaters
- 3m people left without electricity
What were the economic impacts of Hurricane Katrina and responses?
- $125bn damage - most expensive natural disaster in US history
- Widespread looting - police unprepared and national guard needed
- Businesses destroyed leading to high unemployment
- 30 oil platforms damaged -> rising fuel prices
- over 70 countries pledged money assistance to USA with NGO’s such as Red Cross providing assistance
- US gov provided $62bn aid for victims and mobilised 60,000 guard troops
What were the forecasting and satellite technology for Typhoon Haiyan?
- Advanced warnings tracked Haiyan using satellite technology by PAGASA
- Forecasting was fairly accurate but underestimated impact of storm surge - originally given level 1 warning
What were the warning and evacuation systems for Typhoon Haiyan?
- 2 days warning via radio, TV, texts
- 750,000 evacuated before storm
- Many shelters were in low-lying areas so destroyed by storm surge
- Due to communication breakdown after power and phone lines destroyed, some remote communities didn’t receive timely warnings
What were the defences for Typhoon Haiyan?
- No significant levees or sea walls to protect against storms surges
- There were mangroves and natural defences but many had been removed for urban development
What was the environmental impact of Typhoon Haiyan?
- 70,000ha of farmland ruined, 1.1m tonnes of crops lost affecting food supplies
- 30,000ha of tropical mangroves lost, no future protection against storms
- 5m storm surges hitting 6 islands resulting in cut communications and isolated people
- Landslide triggered by heavy rainfall due to steep terrain
What was the social impact of Typhoon Haiyan?
- 7000 deaths
- 2m destroyed homes
- 6m displaced people
- Malnutrition due to destroyed food supplies
- Many poor people lived in coastal slums making them more vulnerable, low-lying areas
- UK provided portable toilets, hygiene supplies and psychological first aid
What was the economic impact of Typhoon Haiyan?
- estimated $6bn cost of damages
- 6 million people lost their jobs
- Rice, corn and sugar-production destroyed, reducing exports
- Tacloban City Airport flooded so planes couldn’t land
- Many people left dependant on aid from NGOs
- $500m raised by UN global appeal
Compare the physical geography of Typhoon Haiyan and Hurricane Katrina
Typhoon Haiyan:
- Category 5
- 5m storm surge
- low lying areas impacted eg Tacloban
- steep terrain leading to landslides
- intensified over strong Atlantic Ocean
- 195mph wind
Hurricane Katrina:
- Category 5 - 3
- 4m storm surge
- low lying areas impacted eg New Orleans
- flat terrain so no landslides
- intensified over warm Pacific oceans
- 175mph wind
Describe how social media could be used to record the impact of a cyclone
Whatsapp etc could be used to post photographs showing cyclone damage
The location of cyclone impacts can be shared
Describe how satellite imagery could be used to assess the impact of tropical cyclones
Before and after satellite images could be compared and used to assess damage to natural and man made features
When does the frequency of hurricanes increase in the North Atlantic region?
More hurricanes in late summer/early autumn as they require sea surface temperatures of 27 degrees which provides them with more energy
Suggest a reason for the overall increase for the frequency of tropical cyclones over time
Burning of fossil fuels leading to global warming, increasing ocean temperatures leading to increased frequency
More accurate monitoring now meaning that more cyclones are recorded so overall frequency increases
