9.3 Hazards resulting from atmospheric disturbances

Question 1

Tropical cyclone characteristics

Answer 1

Surface winds of 74mph+: anti-clockwise in N hemisphere (v.v.)
5-6 miles high + 300-400 miles wide
Typically move at 10-15 mph (but up to 40 mph) but wind speeds within them may reach over 120km (75mph) – slower speed of travel may prolong impacts . An average tropical cyclone can travel about 300 to 400 miles a day, or about 3,000 miles

Question 2

Tropical cyclone definition

Answer 2

An area of low pressure (as low as 880mb) over tropical or sub-tropical waters where trade winds converge at the Inter-Tropical Convergence Zone

Question 3

Tropical cyclone pressure significance

Answer 3

The lower the pressure, the more wind rushes in which powers the storm

Question 4

Where tropical cyclones occur and why?

Answer 4

At latitudes between 5 and 30 N and S (mostly between 5-20 N/S within 500km either side of the Equator) - further out temps fall and mid latitude depressions lead to strong winds stopping thunderstorms from occurring
Sufficient spin

Question 5

Where do tropical cyclones not occur + why?

Answer 5

South America
- ocean is too deep and cold
- Humboldt current makes sea 16C where it should be 30C

Question 6

Where are tropical cyclones most common and why?

Answer 6

East Asia, the Caribbean and the Indian Oceans + Eastern Pacific north of equator

Question 7

Requirements for a tropical cyclone to occur (3)

Answer 7

Warm oceans (26C+)
Sufficient spin from the Coriolis effect
Depth of up to 50m

Question 8

Number of people who live on the coastal rim surrounding the Bay of Bengal

Answer 8

500 million

Question 9

Number of deadliest tropical cyclones that have occurred in the Bay of Bengal

Answer 9

26/35

Question 10

Formation of tropical cyclones

Answer 10

Warm oceans warm the air above and cause evaporation of large amounts of water vapour into the atmosphere
If the surrounding air is unstable, as in colder than the unwarmed air from above the ocean, it will continue to rise through convection as the heated, moist air expands and becomes less dense
- all happens around the ITCZ where trade winds converge near the ocean surface
At about 6 miles above the surface temps cool enough to dew point temperature and the rotating winds (caused by Coriolis effect) spin inwards + upwards releasing heat + moisture so that a cylinder of cumulonimbus clouds form
The winds spiral outwards carrying the cloud outwards, leaving the cyclone core cloud free
Low wind shear (lack of variation in wind speed + direction at different altitudes and lack of wind shear cause by lack of Jet Stream at this altitude allows further uplift and formation of cumulonimbus clouds + thunderstorms
As condensation occurs, 90% of energy in the storm is released as latent heat
This warms the air and causes it to rise further and faster. As the air rises, it leads to low pressure which causes a pressure gradient, drawing more moist air at the surface to fill the low pressure and this drives the storm on.
The lower the pressure, the more air is drawn into it and the greater the power of the storm

Question 11

Why are there stable conditions in the eye of a tropical cyclone?

Answer 11

As air convects upwards + reaches the tropopause, some of it cools and sinks

Question 12

Direction of movement of tropical cyclones

Answer 12

East to west

Question 13

When do tropical cyclones occur?

Answer 13

• May to November in northern hemisphere
• November to May in southern hemisphere- Link to sea surface temperatures which vary seasonally – notice that they extend beyond the peak summer months in each hemisphere due to specific heat capacity of the sea which means that temps remain higher for longer as they cool down more slowly than the land

Question 14

Primary hazards of tropical cyclones

Answer 14

Very low pressure (<920mb)
Strong winds
Torrential rain - fluvial flooding
Bands of thunderstorms
River flooding + coastal flooding

Question 15

Tropical cyclones LICs vs HICs impacts

Answer 15

Most deaths in LICs, most financial losses in HICs
Higher % of GDP in LICs lost

Question 16

Why do TCs stop over land

Answer 16

As it moves over land, its energy source is depleted and friction across the land surface distorts the air flow
This leads to the eye filling with cloud and the TC dies

Question 17

Where are tropical cyclones found?

Answer 17

· They occur at latitudes between 5 and 30 N and S of the Equator (majority between 5-20 N/S within 500km either side of the Equator. Further N or S and temperatures fall and mid latitude (40-60 º)depressions (low pressure systems) would lead to strong winds that would not allow thunderstorms to come together

· Within area of low pressure around the equator the air is heated over the warm tropical ocean. This air rises in discrete parcels, causing thundery showers to form. These showers usually come and go, but from time to time, they group together into large clusters of thunderstorms if low wind shear. This creates a flow of very warm, moist, rapidly rising air, leading to the development of a centre of low pressure, or depression, at the surface.

· They need sufficient spin from the Coriolis effect to form – not enough at the equator.

· They also need warm oceans (at least 26ºC) as the water must be warm enough for sufficient evaporation. Warm air in these tropical areas also holds more water. The subsequent condensation of this water vapour releases latent heat energy which drives storm.

· Notice that they don’t form around South America – ocean is too deep and cold eg Humboldt Current off west coast returning cold water back to Equator – sea is 16ºC in latitude where it should be 30ºC

· They also form on the west side of oceans / east side of continents due to ocean currents and easterly trade winds

· Highest frequencies occur off East Asia, the Caribbean and the Indian Oceans, plus eastern Pacific N of equator. Explanation should be in terms of the high sea temperatures generated in these areas supplying sufficient latent heat for the development of these large intense low pressure areas. Movement is predominantly east to west making low lying eastern coasts the most vulnerable.

· Location: Gulf of Mexico coast/ S.E. United States or Bangladesh Bay of Bengal or any other area where tropical storms hit islands or a coastline.

· Direction of travel and areas affected: Movement westwards is promoted by out flowing air from high pressure systems (the Bermuda high in the case of Atlantic hurricanes) but accept a general movement from the NE and SE trade winds westwards. However, movement is highly complicated and is often erratic.

· Deflection polewards is affected by the blocking land masses and storms die out over cooler sea areas which block their route towards the poles – means that they travel across the oceans from East to west

Question 18

Where and when are they found?

Answer 18

Spatially uneven and not all parts of the world affected if you are comparing to other hazards: 5-30°latitude 80% originate between 5-15°latitudes N/S within or just poleward of the ITCZ. Bay of Bengal especially at risk: The largest bay in the world - 500 million people live on the coastal rim that surrounds it - is also the site of the majority of the deadliest tropical cyclones in world history. According to a list maintained by Weather Underground, 26 of the 35 deadliest tropical cyclones in recorded have occurred here. Temporal distribution – they do not occur all year round, but climate change is changing the pattern The season of tropical cyclone occurrence is related to the shift in the ITCZ with the overhead sun shifting between the tropics. They occur in the summer season in each hemisphere They move westward due to the rotation of the Earth and the easterly trade winds They are a relatively common hazard. There are less in El Nino years and more in La Nina years

Question 19

Why are tropical cyclones hazardous?

Answer 19

• They are hazardous due to the characteristics of the cyclones:

Primary hazards:

· Very low pressure (<920mb) => buildings may explode outwards

· Strong, spiralling winds – high wind speeds over 74mph destroy buildings, infrastructure, cause deaths, carry debris and cause piling up of eye of storm where low pressure is

· Torrential rain concentrated around the eyewalls – can lead to fluvial flooding and this can extend inland even though they typically die out as they hit the coast

· Bands of thunderstorms (and hailstorms) associated with towering cumulonimbus clouds

· Storm surges – large scale coastal flooding make them hazardous in low lying, densely populated coastal areas.

· Flooding due to torrential rain (river flooding) and storm surges (coastal flooding)

· Particularly hazardous when the storm surge is combined with high tide causing coastal inundation. Combined with river floods from high rainfall, there is a multiplier effect- high discharge in rivers inter-plays with coastal flooding in lowland areas.

Secondary Hazards:

· Secondary hazards such as mudslides (linked to heavy rain- shear stress v shear strength and increased pore water pressure

Question 20

Tropical cyclone hazards + impacts overview

Answer 20

These phenomena can cause major destruction, especially when the tropical cyclone’s path takes it over land. However, a path over land also causes the destruction of the tropical cyclone itself. As it moves over land, its energy source is depleted and friction across the land surface distorts the air flow. This leads to the eye filling with cloud and the tropical cyclone dies. Major threat to coastal areas, especially in densely populated low-lying delta areas, most notably Bangladesh. Also isolated island groups eg Philippines, Japanese and Caribbean islands, densely populated coastlines of Gulf of Mexico, Atlantic coastline of USA and Queensland Gold Coast of Australia. Typically, most deaths in LICS, most financial losses in HICs although as % of GDP probably higher in LICs. Financial losses in LICs often confined to loss of cash crops and livestock and disease is much higher due to decaying bodies of livestock – agricultural economies most affected Multiple hazard – composite hazards - as loss of life and damage to property may result from winds, heavy rainfall and storm surge

Question 21

Tropical cyclone wind hazard

Answer 21

Question 22

Tropical cyclone heavy rainfall hazard

Answer 22

Heavy Rainfall and Inland Flooding

heavy rain - the tropical cyclone can pick up two billion tons of moisture per day and release it as rain. This also leads to extensive flooding - often well inland from where the tropical cyclone hit the coast

May produce widespread , torrential rains in excess of 15 cm which may result in deadly and destructive floods.

Flooding is the major threat from tropical cyclones for people living inland.

Flash flooding may occur quickly due to intense rainfall. Rainfall amounts are not directly related to the strength of the cyclone but rather to the speed and size of the storm as well as the geography of the area – slower moving and larger storms produce more rainfall. In addition, mountainous terrain enhances rainfall from a tropical cyclone (orographic rain and speeds up surface run off) Can lead to secondary hazards like flooding and land-sliding

Typical levels = 100mm per day within 200km of the eye so large area affected and 40mm per day between 200 and 400km of the eye.

Super-typhoon Durian, a category 5 storm, affected the Philippines in Nov. 2006. Nearly all the 1200 deaths occurred when torrential rains saturated volcanic deposits on the slopes of the Mayon volcano, causing mudflows that raced down the steep slopes onto the towns beneath. People had no time to escape as entire villages were buried under volcanic debris.

Question 23

Tropical cyclones storm surge hazard

Answer 23

Storm surge and large waves produced by hurricanes pose the greatest threat to life and property along the coast.
Storm surge is an abnormal rise of water generated by a storm’s winds. Storm surge can reach heights well over 20 feet and can span hundreds of miles of coastline
Storm tide is the water level rise during a storm due to the combination of storm surge and the astronomical tide
Cause 90% of deaths and extensive damage to agricultural land by contamination from inflowing sea water. Greatest effect on low-lying coasts eg 2005 Hurricane Katrina’s storm surge caused levees to break flooding 80% of the city killing 2000 people. Storm surge is caused by wind driving the ocean surface ahead of the storm (85-90% of the storm surge) and low pressure which is responsible for 5% of the cause– this allows the sea level to rise – it rises 260mm for every 30mb drop in pressure. The low pressure influences the height of the storm surge – the lower it is, the higher it is. Affected by: coastal topography with shallow continental shelf, speed of the cyclone, height of tide, wind strength, absence of features like spits to deflect energy then landuse, type of building, crop type, pop density, vulnerability and preparedness. The surge will be especially high if:
· The storm has strong onshore winds
· It approaches the coast at a right angle (perpendicularly) so head on to the coast line
· The coastline has headlands and bays and inlets which will cause water to be funnelled in and so increase the water height (seiching)
· The sea floor is gently sloping with a wide continental shelf
· There are few obstructions such as spits and islands to slow the flow of water
· The storm coincides with high tide - New York City and New Jersey experienced exceptional storm surge during Hurricane Sandy partly because the storm made landfall close to high tide under a full moon. During this phase of the moon, high tides can rise about 20% higher than normal. Enclosed areas of water eg bays may be affected adversely due to funnelling which leads to seiching – where strong winds cause waves to oscillate and produce tsunami-like waves
· Flooding due to torrential rain (river or fluvial flooding) and storm surges (coastal flooding)
· Particularly hazardous when combined with high tide causing coastal inundation. Combined with river floods from high rainfall, there is a multiplier effect- high discharge in rivers inter-plays with coastal flooding in lowland areas.

Question 24

Influence of local geography on storm surge

Answer 24

Once again, local geography important

• Hazard is not just about winds. In fact, storm surges leading to flooding are more hazardous.
• Huge volumes of water are pushed by hurricane-force winds towards the shore.
• Also low pressure means high tide is higher in any case-which exacerbates impact.
• When they meet land, the water surges inshore at levels far exceeding normal tides.
• Consider how climate change may affect this
• In New Orleans, 2005, Hurricane Katrina’s storm surge caused levees to break, flooding 80% of the city and killing 2000 people

Question 25

How are wind speeds measured in tropical cyclones - classification

Answer 25

Saffir-Simpson scale
Category 1: Winds 74-95mph
Category 2: Winds 96-110mph
Category 3: Winds 111-129mph
Category 4: Winds 130-156mph
Category 5: Winds 157+mph

Question 26

Saffir-Simpson overview

Answer 26

Tropical storms are the most violent, damaging and frequent hazard to affect many tropical regions.
They are measured on the Saffir-Simpson scale, which is a 1-5 rating based on intensity. It is used to give an 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 the landfall region. They can also cause considerable loss of life e.g. Cyclone Nargis, Myanmar (138,000 deaths); Typhoon Haiyan (6, 340)

Question 27

Other ways to measure cyclone intensity

Answer 27

Additionally, the Dvorak technique has also been developed to estimate cyclone intensity on a scale from 1-8. It is based on satellite images of patterns of weather systems, in particular the difference between the temperature within the eye and the coldness of the surrounding thunderstorm clouds

It is important to note that whilst the Saffir-Simpson Hurricane Wind Scale defines wind strengths and their likely impacts, severe impacts from tropical cyclones can also occur due to storm surge and heavy rain which are not necessarily directly related to the strength of the wind in the tropical cyclone.

Question 28

Conditions needed for the formation of tropical cyclone + eval

Answer 28

1. Ocean with surface temps over 26C with warm water to a depth of 60-70m. This is crucial as there must be a supply of latent heat and moisture to provide energy and ensure that the outflow of air from the upper atmosphere is replaced by an inflow at ground level. The sea also provides a surface with low frictional drag so energy is not lost – when the storm moves over a cooler ocean surface or land where friction increases, the storm will start to decay as the heat and moisture supply to sustain convection is lost
2. Instability and humidity– disturbance in lower atmosphere’s circulation as warm, humid air meets cooler air and starts to rise with convection
3. Low wind shear – winds at all levels in the same direction – allows thunderstorms to cluster
4. A large enough Coriolis force to produce a circular pattern of winds
5. Excess heat is transferred away from the storm by upper-atmosphere wind

Question 29

How tropical cyclones develop

Answer 29

• In the tropics there is a broad zone of low pressure which stretches either side of the equator – the ITCZ. The NE and SE Trade winds converge here. This is often at the boundary between cold air and warm moist air masses creating unstable air
• The converging trade winds cause instability so that warm air parcels rise due to convection and storm clouds to form. Low pressure is left at the surface.
• Energy and water from sea temperatures of 26oC and ocean depth of 60m+ (in late summer) lead to evaporation and convection => moist air rises => leads to storm clouds forming.
• Rising, unstable air => creates extreme low pressure at surface around eye of storm ( with pressures below 920mb and as low as 880mb)
• Winds blow from high pressure to low pressure along a pressure gradient
• Rising air takes in latent heat as moisture evaporates and this drives the storm.
• As the warm, unstable air rises, it cools and condenses and so latent heat is released from condensation => this warms the air so it rises further and more rapidly => creating towering cumulonimbus clouds and lower pressure at surface
• This causes an area of low pressure at the surface and thundery showers to form. These showers usually come and go, but from time to time, they group together into large clusters of thunderstorms if there is low wind shear. (winds that do not vary much in height and direction).
• Low wind shear: winds in upper troposphere must be strong enough to transport excess heat way from storm (air moves away) but not strong enough to remove top of storm system (allows the storm clouds to rise vertically to high levels)
• These thunderstorms must cluster at a sufficient distance from the equator to provide spin or twist.
• At 5-30 N/S , the Coriolis force caused by the rotation of the Earth helps the spin of this column of rising air. The development of the surface low pressure causes an increase in the strength of the trade winds. The spiralling winds accelerate inwards and upwards, releasing latent heat and moisture as they do so.
• Moist air in mid-troposphere (5km above surface) – provides extra water vapour which is evaporated and takes in latent heat => this latent heat drives storm on further
• As the depression (Low pressure system) strengthens it becomes a tropical storm and then a hurricane or typhoon. A mature hurricane or typhoon takes the form of a cylinder of deep thundercloud around a centre that is relatively free from clouds. There is a relatively small area of intense horizontal winds at the surface, often well over 100 m.p.h., while air rises strongly above, maintaining the deep cumulonimbus clouds.
• Further aloft at about six miles, the cloud tops are carried outwards to give thick layer clouds due to the outward-spiralling winds leaving the tropical cyclone core. At the centre of the tropical cyclone, air is subsiding, which makes it dry and often cloud free, and there is little or no wind at the surface. This is called the eye of the storm

Question 30

Tropical cyclone formation diagram

Answer 30

Question 31

Where is the risk from tropical cyclones greatest?

Answer 31

Greatest risk from tropical cyclones is at the coast as energy is lost over land. The slower the cyclone, the greater the damage (speed of onset and duration). Also, in the northern hemisphere, the greatest risk is for cities on the right of the eye’s path because there the travel speed is added to the speed of the winds that are rotating anticlockwise.

However, sometimes conditions on the land can resemble the moist environment of the ocean maintaining and even increasing the power of the storm. This is the ‘brown ocean effect’

Question 32

Brown ocean effect

Answer 32

It is rare, but the brown ocean effect refers to when a tropical storm or cyclone maintains or even intensifies in strength as it moves inland, contrary to the usual behaviour of such systems which tend to fragment and peter out once they make landfall. As most tropical storms or cyclones get their energy from warm sea water and weaken once they cross the coast and lose their usual source of heat and moisture, and hence energy, from the sea. So for most tropical storms/cyclones the largest amounts of rain are usually recorded before or on landfall.

Some cyclones remain energised or intensify once they make landfall. Recent scientific research has found that three conditions appear to be necessary:

1. The ground must be very warm and have a similar temperature to the sea from where the tropical storm or cyclone has come from.
2. The ground must be very wet or saturated and so this land ‘mimics’ the sea - and hence the name ‘brown ocean effect’. The high amount of moisture in the soil, then allows a high rate of evaporation, which then acts as a source of heat energy for the storm or cyclone, technically known as latent heat - similar to the process over the sea.
3. The amount of this latent heat must be at a certain level - at least 70 watts per square metre. Over the sea it would normally be around 200 watts per square metre

Question 33

Effect of frequency on tropical cyclone hazard

Answer 33

The degree of hazard from tropical cyclones depends partly on how frequently they occur in the same area, their magnitude and the location of the area affected. The most powerful storms are not necessarily the most hazardous.

Question 34

Tropical Cyclone Management Prediction & Warning

Answer 34

· Coastal areas at risk from tropical cyclones are protected by warning systems. These monitor tropical cyclone development and forecast their intensity and tracks so population can move to shelters or evacuate their property from the danger area
· HICs most protected due to cost of technology and communications.
· US has most developed warning services –National Hurricane Centre (NHC) in Miami, Florida
· Data is collected from geostationary satellites and land and sea-based recording centres – in real time and constant. If a storm develops, more accurate data is collected by reconnaissance flights. The data is then sent to NHC to be analysed by super-computer.
· NHC issues tropical cyclone advisory information at least every 6 hours at 5 am, 11 am, 5 pm, and 11. Watches give updates every 3 hours and communicate on TV, radio, and cell phones; and NOAA radios – has 1000 transmitters covering all 50 states
· Even less developed countries have early warning systems eg India’s Cyclone Warning and Dissemination Systems (CWDS) implemented along the Andhra coast in 1978 reduced the death toll eg category 5 storms in 1977 – 10,000 deaths v 1000 deaths in 1990.
· Predictions and forecasts are based on statistical models of hurricane activity and previous tracks and global climate data and ocean surface temperatures to make predictions – stresses the importance of sea temps.
· The track of the hurricane is better predicted than its intensity. Predicting the intensity accurately remains an outstanding challenge of meteorology. There is a cone of uncertainty in prediction -The cone represents the probable track of the centre of a tropical cyclone- Based on forecasts over the previous 5 years, the entire track of the tropical cyclone can be expected to remain within the cone of uncertainty roughly 60-70% of the time.
· Once these cyclones reach land, they are less easy to predict because they interact with weather systems over the land
· However, if prediction proves wrong – there are high economic losses due to evacuation and too many false predictions may result in complacency and affect perception of risk– Much progress to address this in India - the uncertainty in 5 day prediction in India has been reduced by 30% between 2014 and 2018 which has reduced the evacuation area by 300km which has reduced economic losses when prediction is wrong by 60%.
· Timing is crucial in hurricane forecasting – as pop densities along coastlines increase, evacuation takes longer and exit roads are put under strain eg Lower Florida Keys are over 100km from closest mainland and could take 31 hours to evacuate along the main highway – this is longer than the prediction with accuracy time that scientists have and warning times are rarely issued more than 12-18hrs before landfall. Believed that a city would take 72hrs to evacuate
· Once predicted, communication to the wider audience is key.
· Need to emphasise though, that whilst early warning systems can save lives, they cannot minimise the socio-economic impacts of recurring disasters. Many lives were saved by advanced warning and shelters ahead of the arrival of Cyclone Amphan, Bangladesh in 2020, but it still left an estimated half a million homeless,

Question 35

Tropical cyclone community preparedness

Answer 35

· *****Despite the advances in prediction and warning, the public needs to know how to prepare themselves and protect their property – even with prediction, people may not evacuate the area or move to shelters due to personal perceptions of risk, cultural or economic factors ….. Perception of risk:
· Those who have never experienced a hazard will conform to the norm and are less likely to heed evacuation advice – in Hurricane Andrew, Florida in 1992, some did not evacuate as a cyclone had never reached that far in land before but

Hurricane Andrew hit and 15 died and 80000 homes were destroyed. Dissemination of warnings is crucial:
· However, some groups in society will be difficult to reach: In India, warnings are issued by telephone, tv or digitally to those who have signed up to the app. Many poor communities eg fisherman in Godavari Delta do not have access to these – surveys have suggested that only 30% of fishermen carry radios and these may be with a weak signal
· Evacuation is also challenging as not all communities are connected by all-weather roads
· National Weather Service in US gives information on strengthening your home, updating insurance policies and devising evacuation plans
· Bangladesh is a good success story for monitoring and prediction with effective communication
· The death toll from extreme weather events has drastically decreased thanks in large part to a multi-layered early warning system consisting of weather monitoring equipment, communication systems and a comprehensive network of volunteers. Crucially, half of these volunteers are women, who are working hard to overcome the huge gender disparities in who is most impacted by disasters.
· Prediction and forecasting investment began in 1970, when Cyclone Bhola resulted in the death of an estimated half a million people in the Bay of Bengal – one of the deadliest storms ever recorded.
· The disaster prompted Bangladesh to begin investing heavily in weather forecasting technology, cyclone shelters and training up a network of volunteers along the coast.
· When Cyclone Amphan made landfall in 2020 as a strong Category 2 cyclonic storm – almost as severe as Bhola’s Category 3 – it recorded a death toll of just 26.
· This was due to warnings of a depression forming over the Bay of Bengal 2 days before Amphan which was tracked and communicated on social media and led to evacuation
· Bangladesh’s success in lowering its death toll is due, in part, to this improved ability to monitor and track cyclones as they form over the Bay of Bengal. In 1970, the country had only two coastal radars, with an ability to track the progress of cyclones once they were within 200 miles (322km) of the coast. Today, a comprehensive network of weather stations, including coastal radars, ground-based stations and balloon-borne instruments measuring air pressure and humidity enable Bangladesh to closely monitor developments in real time. But simply having the data is only one part of effectively warning people about the dangers coming their way. Ensuring this information actually reaches them is another huge component. “Even if you have the best science, the best predictions available, if it’s not translated into the right language or format for the community they won’t understand,” “[It] has to be built with that local perspective from the very start.”
· Bangladesh’s early warning systems uses a variety of communication methods: TV and radio broadcasts, push messages via mobile phone networks, targeted SMS notifications, and a helpline which people can dial to listen to pre-recorded voice messages. But the key to reaching as many people as possible – known as “the last mile” by disaster risk reduction experts – lies in the country’s huge network of volunteers.
· Bangladesh Red Crescent Society set up a cyclone preparedness programme (CPP), with over 76,000 volunteers in villages along the coast.
· They are responsible for making sure that everyone in their community is aware of the latest weather risk warnings. Volunteers use a tiered flag system, displayed in the central marketplace or village square, to communicate the severity of the storm. They also patrol through the streets with megaphones to disseminate the warning, and even go door-to-door by foot or motorcycle to ensure that the information reaches everyone – including those who are homebound, illiterate or without access to a mobile phone.
· Several studies have found that during disasters, a community-led response – with government and non-profit support – is essential for the rapid, widespread action which saves lives.
· In the past year, the CPP has attempted to extend the last mile approach all the way down to schoolchildren, initiating the Prostoot or “learning through playing” programme in some secondary schools. The schools run dedicated disaster-preparedness days, where they do evacuation simulations throughout the day. Children also learn basic first aid and form disaster management teams. The goal is to create a “disaster-ready generation”. Gender disparity
· The ability to quickly spread information at a local level has been particularly important in saving the lives of women, who across the globe are often disproportionately affected by sudden-onset disasters.
· Gender inequality results in lower literacy rates, gendered roles which confine women to the home, and less decision-making power in the household, limiting women’s access to information, “The early warnings that the women and girls receive are often filtered through the male members of the family,” “It is not properly disseminated to the female.”
· This has led to women often being over-represented in death statistics from cyclones in Bangladesh. During Cyclone Bhola in 1970, female deaths outnumbered males by 14:1. This was compounded by many women choosing not to evacuate in the belief that their place was in the home, or out of a fear of gender-based violence in overcrowded shelters – this affects their perception of risk .
· women often feel that it would bring dishonour to the family to stay in a shelter without male guardians to accompany them.
· Female volunteers have increased in Bangladesh – women are able to access spaces that men might not, ensuring that vital messages about incoming cyclones are spread among female networks which might otherwise remain isolated, As a result, the ratio of male to female deaths in disasters has been falling in recent years, and during Cyclone Amphan in 2020 decreased to 1:1,

Question 36

Landuse planning And Hazard mapping to assess risk tropical cyclones

Answer 36

· Most effective in the coastal zone at risk from the storm surge.
· Past cyclone data and coastal topography can be used to identify high-risk areas
· Aim is to limit development in these areas or make them more compatible with flooding such as beaches or parkland and put most important facilities (emergency, comms, roads, power stations) in least vulnerable places
· However, in LICs space is a commodity or people live by the coast for their living eg fishermen or tourism as in the Philippines
· poorer most disadvantaged may live in marginal areas of land and may be dependent on coast for living , or they may live in temporary accommodation eg trailer parks etc , on steep slopes or river floodplains – you can hazard map the areas but sometimes it is not possible to move people who are forced to live there as have little choice
- Also, aerial extent maybe too large to manage ie 800km across,
· need to understand that on coastal areas, storm surges most hazardous and can stretch for 100s of miles whereas inland fluvial flooding due to high rainfall more hazardous all over the area and winds can affect areas 100 miles in land eg Hurricane Charlie in 2004 – affected Florida with gusts upto 100mph inland

Question 37

Hazard Resistant Design tropical cyclones

Answer 37

· This protects against the storm surge and wind hazards
· Impacts of the storm surge hazard may be reduced by engineering structures eg sea walls, flood barriers – Galveston, Houston, Texas was actually elevated by 3.5m – but it was very costly and took 7 years so unlikely to be repeated ever again
· As well as being costly, this protection can also give a false sense of security and distort perception of risk even if it is inadequate – New Orleans built on the Mississippi Delta which is 3m below sea level – flood walls and embankments collapsed when Hurricane Katrina, a category 5 storm, hit in 2005 – the defences were only designed to withstand a category 3 storm – 80% of the city was inundated and 1800 deaths. The main cause was flooding due to the storm surge and rain – interestingly buildings withstood the wind speeds.
· Buildings may be raised on stilts and use concrete/brick rather than wood which is more easily swept away. – storm shelters – but people need to know about these and be able to access them – many people in poorer parts of the world will not leave their belongings or their livestock so perception affects this form of management
· ‘Shelter-ready Bangladesh’
· These shelters are themselves another huge part of Bangladesh’s success in reducing the risks to people of extreme weather. Through them Bangladesh has excelled at offering people clear and accessible means to protect themselves when they receive warnings.
· In 1970, Bangladesh had just 44 cyclone shelters. But in the wake of the Bhola disaster in 1970, and with the combined efforts of the government and international aid, this had increased to almost 4,000 formal shelters by the mid-2000s. Most double up as schools and community centres.
· A study published last year found that Bangladesh’s combination of increased access to shelters and community management has helped to improve evacuation behaviours.

Question 38

Hurricane Mitch, 1998 - Honduras + Nicaragua case study

Answer 38

LIC , slow moving so impact of rainfall was severe and caused most of the impacts, local geography led to increased rainfall and triggering of secondary hazard of landslides which killed many people and damaged crops

Scale:
- 5 Saffir Simpson Scale, top 5 Atlantic hurricanes ever Pressure: 905mb Winds 180mph
- Was predicted and tracked but took a more westerly path despite predictions to the north and unclear which countries would be hit

Impacts:
- 11,000 deaths $10billion damage, collapse of volcanic crater that sent an debris flow of mud which buried 80km²and killed 2000 people
- Honduras Homeless : 600,000 – 10% of population 85% infrastructure destroyed 70% crops destroyed such as cash crops like bananas – food insecurity and trade affected
- Cost to agriculture: $2 billion Long term: Set the economy back 50 years
- Widespread landslides and flooding

Main Hazards:
- Huge amounts of rainfall due to storm’s slow movement – it became stationary for 24 hours along with orographic effects of the Central American mountains. Rainfall duration and intensity were exceptional – when Mitch made landfall, it rained for 61 hours with intensities of up to 584mm/hr. Led to secondary hazards with widespread flooding, rivers changed course and landslides triggered
- Exacerbated as soil saturated as occurred at end of wet season
- Mountainous terrain and agricultural practices and left slopes unstable and soils exposed so floods and landslides caused most deaths and loss to crops

Management:
- International aid – after the event totalling over $100,million along with personnel like airforce and drs.
- International Red Cross raised an appeal for $4.5million

Question 39

Hurricane Katrina, 2005 - New Orleans case study

Answer 39

HIC – prediction and yet poorly managed – poor perception of risk, poverty- some groups more affected than others, acting on evacuation advice long term impacts, local geography (human and physical) increased vulnerability, flooding not winds main hazard

Scale:
- Made ground-fall at Grand Isle 90km south of New Orleans 200km winds along 200km stretch of coastline Category 5 storm declared only 2 hours before it reached the coastline Storm surge – 6m and inundated 80% of the city due to coastal and river flooding
- Storm surge overtopped levees and destroyed 50 before flooding residential areas

Local geog exacerbated the impacts
***Local geography made the area more vulnerable:
- New Orleans has always been vulnerable to flooding, it sits by Lake Pontchartrain and the Mississippi river for a start.
- The wetlands of the Mississippi delta that used to protect New Orleans have diminished in size because they have been drained and because they are starved of sediment because the Mississippi river is so heavily embanked against flooding it stops erosion upstream which prevents deposition downstream.
- New Orleans is also sinking! The drained soft sediments it is built upon have compacted under the weight of the buildings, and the draining of water that supported the structure of the soil has also had an impact.

Impacts:
Social:
- 1200 deaths – one third by drowning due to nature of the hazards and bulk due to disease (secondary or even tertiary impact)displaced over one million people from the central Gulf coast elsewhere across the United States. For example, Houston, Texas, had an increase of 35,000 people putting pressure on cities beyond New Orleans
- These people were displaced long term – US Census in 2006 showed 5% drop in population and this impacted poorer, Afro-Caribbean people the most with children losing a year of schooling and communities broken up
- Longterm: Widespread housing damage prevented residents’ returning: 72% percent of the 188,000 housing units in Orleans were damaged, with 56% percent having major or severe damage

Economic:
- $105 billion needed for repairs and reconstruction in the region interruption of the oil supply, destruction of the Gulf Coast’s highway infrastructure, and exports of commodities such as grain. Katrina damaged or destroyed 30 oil platforms and caused the closure of nine refineries – affected oil supply; -1.3 million acres (5,300 km2) of forest lands were destroyed costing about $5 billion
- It is estimated that the total economic impact in Louisiana and Mississippi may exceed $150 billion
- Additionally, some insurance companies have since stopped insuring homeowners in the area because of the high costs from Hurricanes Katrina and Rita, or have raised homeowners’ insurance premiums to cover their risk

Environmental:
- The storm surge caused substantial beach erosion, in some cases completely devastating coastal areas. eg Dauphin Island the barrier island was transported across the island into the Mississippi Sound, pushing the island towards land
- Lands lost were breeding grounds for marine mammals, brown pelicans, turtles, and fish
- Oil spills from 44 facilities throughout southeastern Louisiana, which resulted in over 7 million U.S. gallons (26 million L) of oil being leaked.
- Finally, as part of the cleanup effort, the flood waters that covered New Orleans were pumped into Lake Pontchartrain, a process that took 43 days to complete. These residual waters contained a mix of raw sewage, bacteria, heavy metals, pesticides, toxic chemicals, and oil, which sparked fears in the scientific community of massive numbers of fish dying

Political:
- Racial tensions - government criticised for its response, with many critics claiming it was very slow to respond and that the management lacked coordination.
- The use of emergency centres was also criticised, with the Louisiana Superdome (designed to handle 800, yet 30,000 arrived) and the New Orleans Civic Center (not designed as an evacuation center, yet 25,000 arrived) deemed by many as inadequate.
- Structural racism: Race and class were also stipulated as issues, with Kanye West claiming that there was a racial reason for the slow response, given that most of the stranded people were African American.

Main Hazards:
- Winds 200km/hr but main issues were storm surge of 6m which overtopped levees built only for a category 3 storm – 50 failed and 80% of city of New Orleans inundated causing flooding and 1/3 of casualties drowned

Management:
Before the event:
- Prediction/forecasting: The storm was predicted by the National Hurricane Centre and they gave a very accurate plot of the Hurricane’s track and expected landfall, not far from New Orleans. This allowed for a coordinated EVACUATION
- The mandatory evacuation order by FEMA (Federal Emergency Management Agency) issued the day before required that all residents leave the city.
- About 70 % of the approximately 452,000 residents in the city of New Orleans did evacuate but many people were left behind and many refused to move.
- 5 % never evacuated. African Americans were the majority of the small group who never evacuated.
- Risk perception affected evacuation: Risk perception and response are also important in understanding why people may not have evacuated, although these are linked to a lack of resources also - 49 % of New Orleanians who did not evacuate said they did not think that the hurricane would be as bad as it was and 21 % reported they lacked finances or a car that would have allowed them to evacuate - Risk perception is influenced by the fact that New Orleans residents had experienced hurricane warnings before, with many close calls and non-events but very rarely a direct hit. Further, it was not the weather event itself but the flood caused by the failure of the levees which meant so many of them had to evacuate - - Takes 72 hrs to evacuate a city – but depends on pop. size, density, wealth car ownership etc

After the event:
- Approximately 58,000 National Guard personnel were activated to deal with the storm’s aftermath, with troops coming from all 50 states.
- The “draining” of the below-sea-level city took six weeks and was prolonged when Hurricane Rita added rain to the floodwaters on September 25.

Question 40

Super Typhoon Haiyan – Philippines 2013 case study

Answer 40

MIC -high social costs but economic costs still relatively high, accurately predicted but poor rates of evacuation and access to shelters, issues in managing multiple hazardous areas – caused by Bohol earthquake a month before, local geography exacerbated impacts, main impacts from storm surge as a hazard not rain or winds

• Scale 5 Saffir Simpson Scale Dvorak 8.1 (off the scale as so intense)
• Pressure: 930mb
• Winds 314km/hr
• Storm surge: 7 m
• A storm impacting a coast with a shallow and gently sloping seabed will create a higher surge if its approach is perpendicular to the shore rather than at a more oblique angle to the shore and/or the seabed is steeper. Coastal orientation also matters, as a large volume of water forced into a narrow bay or inlet will mound up even higher.
• Haiyan passed over the Leyte Gulf—which narrows at its northern end to form San Pablo Bay—heading almost directly for Tacloban City. Because of the storm’s track and extreme onshore winds, and the bathymetry and orientation of San Pedro Bay, an exceptional storm surge was funnelled into the shallow bay between Leyte and Samar islands and into Tacloban City.
• The contours of the coastal landscape determine how far inland storm surge will penetrate. Steeper slopes lead to more rapid weakening of the surge, but low-lying terrain will enable surge to penetrate far inland. (During Hurricane Ike in 2008 surge was able to reach nearly 30 miles into some parts of Texas). Most of Tacloban’s populated area is less than 5m above sea level, and there were no coastal defences to stop the surge from inundating the city.
  Impacts:
• Made landfall at Guiuan
• 11,000 deaths , 11 million people affected
• 2 million homeless
• $2.9billion total cost of damage – but nb that GDP per capita only $3485
• 90% towns destroyed
• Airport damaged – only allowing 20 flights a day which hampered relief efforts
• Disease prevailed and power was cut – 4 provinces including Leyte had no power as power lines were destroyed by winds and storm surge
• 20,000 people never returned

Main hazards:
- Fortunately, fast moving so rainfall did not have the usual devastating impact often seen in the Philippines (in 2006 Typhoon Durian had caused 1200 deaths all from landslides triggered by rainfall on the unconsolidated geological slopes of volcano Mayon)
- Winds were severe but worst impacts came from storm surge and coastal flooding.
- This was at 5m but in island areas of Samar and Leyte where land is less than 5m above sea level and in a bay area, seiching occurred, where tsunami like waves were caused by the funnelling in the enclosed waters of the bay leading to storm surges of 7m.
- Tacloban was especially affected including the Tacloban City Convention Centre which was the designated evacuation centre.
- Tacloban’s population had trebled in recent years so density made impacts worse
- 90% of the wooden buildings in the poorest parts of Tacloban were washed away
- Some areas already suffering from after-effects of Bohol Earthquake 7.2Mg which left 5000 people living in tents – multi-hazardous areas more difficult to manage
- Flooding drowned people in the streets

Management:
- Before the event – prediction Accurately predicted , warnings issued and shelters opened
- However, only enough shelters for 0.5 million people and warnings were not made mandatory
- Perception affected people’s willingness to evacuate – afraid of leaving their belongings due to risk of looting and evacuation fatigue due to previous earthquake
- After the event Emergency supplies decimated a month earlier due to the Bohol earthquake
- Aid difficult to access due to limited flights out of airport (20 a day ) as a result of no power Philippines – archipelago of 7000 islands so challenging to get relief to all areas especially as communication lost – had to rely on satellite images
- Mangrove forests were replanted along coast to protect against winds and storm surges – evidence of sustainable management in Philippine

Question 41

Cyclone Yasi, Australia, 2011

Answer 41

HIC, good management, main impact from storm surge and coastal flooding, evacuation heeded, quick recovery, main impacts economic

Scale:
- 5 Saffir Simpson Scale Dvorak 6.5
Pressure: 930mb Winds 285km/hr
Storm surge: 7 m 300km inland but did not coincide with hightide so was 2m lower than forecast
- Speed – 35km/hr so rainfall not as much of an issue as passed through
- Main hazard – flooding caused by storm surge

Impacts:
- 1 death , 400 thousand people affected
- 2 million homeless
- $3.6 billion total cost of damage
- 4000 buildings damaged Impact to agriculture – sugar cane and banana – 75% loss to banana exports but all trade resumed 1 yr later
- Rainforest destroyed so cassowary lost habitat - Great Barrier Reef affected by rainfall as runoff led to pollution which led to outbreak of crown of thorns starfish

Main Hazards:
- Storm surge of 7m inundated 300km inland
- Roofs ripped off and Tully High School destroyed
- Unusual speed of 35km/hr meant rainfall not as much of an issue but all areas received excess of 200mm and Mission Beach received 430mm so flooding was an issue in some parts and the main management challenge was getting emergency relief to communities isolated by flooding

Management:
Before the event – prediction
- Accurately predicted, warnings issued to people along low-lying Queensland coast including people in Cairns and as far south as Brisbane
- 4th cyclone of season and aware that heavy rainfall associated with La Nina over the previous 3 months had saturated soils and so rainfall could have had a significant impact and caused secondary hazard of flooding so evacuation area extended to Brisbane 29,000 people did.
- Evacuation orders issued via media and warnings for storm surge at high tide were issued
- Strict building codes had been enforced since 1974 when a cyclone in Darwin killed 74 people

Question 42

Explain the variations in the warning time and hazard duration shown in Fig. 7.1 (7)

Answer 42

Question 43

Contrast the warning times and hazard durations shown in Fig. 7.1 (3)

Answer 43

Question 44

Tornadoes definition

Answer 44

Rapidly rotating vortex/column of air rotating at destructively high speeds, usually accompanied by a funnel-shaped downward extension from a cumulonimbus cloud down to the ground. Winds blow from 40-300mph. They result from the interaction of air masses with different characteristics of temperature, density, humidity and wind flow.

Question 45

Tornadoes typical characteristics

Answer 45

20-100 m wide at surface and always less than 600m (whereas 500-700km for a tropical cyclone- these are the most violent atmospheric storms but because of their smaller size and because they are short-lived, damage is high but the area affected is smaller)
Lasts for a few minutes but may last for longer. No certainty on why they die out – there must be some break in temperature, moisture, unstable air or vorticity
Track length of around a mile (1.6km) - usually less than 4km
In USA tend to move from SW to NE but can take erratic paths
Localised & short-lived: a typical twister damages an area of only about 13 km² – limited by tornado track (<4km length) and only a few 100m in diameter; lasting several minutes – (important if comparing with effects of tropical cyclones) Lightening, hail or very heavy rain can accompany them

Question 46

Tornado vs tropical cyclone comparison

Answer 46

• The most obvious difference between a tornado and hurricane is that a hurricane’s horizontal scale is about a thousand times larger than a tornado. In addition, hurricanes and tornadoes form under different circumstances and have different impacts on the atmosphere.
• Tornadoes are small-scale circulations, that are rarely more than a few hundred metres across when they touch the ground.
• Most tornadoes grow out of severe thunderstorms that develop in the high wind-shear environment of the United States Central Plains (over land) during spring and early summer.
• Many tornadoes form when the large-scale wind flow leads to a violent clash between moist, warm air travelling north from the Gulf of Mexico and cold, dry, continental air coming from the United States Northwest. Tornadoes can also form in many other locations and from other forcing factors. For example, a hurricane making landfall may trigger many tornadoes to form. Tornado wind speeds may reach 100 to 300 mph and cause havoc on the ground, but tornadoes typically last only a few minutes and rarely travel more than 10 or 20 miles along the ground.
• Tornadoes have little impact on the global circulation of the atmosphere. Hurricanes, on the other hand, are large-scale circulations that are 60 to over 1,000 miles across.
• Hurricanes form near the Equator, generally between 5 and 20 degrees latitude, but never right on the Equator. Hurricanes always form over the warm waters of the tropical oceans and generally where the sea-surface temperature exceeds 26°C

Question 47

Where and when are tornadoes found?

Answer 47

• Spatially uneven and not all parts of the world affected if you are comparing to other hazards:
• Tornado reports are concentrated between 20-60°latitude N/S – India, Bangladesh, Australia, NZ and even UK.
• Equatorial regions lack the contrasting air masses required for their development and insufficient Coriolis force needed to develop their circulation although the role of Coriolis is questioned.
• Polar regions lack warm, moist air necessary for their development.
• 80% and the almost all violent ones originate in the USA
• The area of the Great Plains in the USA is named Tornado Alley - central United States (L-shaped region): western Iowa down through Nebraska and Kansas to southern Oklahoma and then over Arkansas and Louisiana to south-eastern Mississippi
• This area experiences the temperature differential in contrasting and converging air masses from the Rockies and Gulf of Mexico.
• As air travels over the Great Plains, there is no variation in altitude to cause warm, moist Gulf air to rise and cool so it maintains its characteristics until it meets the cold air mass descending over the Rockies.
• Temporal distribution – they do not occur all year around but climate change is changing the pattern
• USA – between mid-March and August
• Shift from the south to the north: Southern states, including the Gulf Coast, are most at risk from March to May, while the southern plains (further north) face the greatest threat from May through to early June. This emphasises the role of temperature differential in their formation.
• UK – September and January when the contrasts between the air masses are most marked

Question 48

Conditions needed for tornado formation

Answer 48

1. They are found in temperate continental interiors in spring and early summer when insolation is strong and the air may be unstable
2. Warm moist air – usually over 18C
3. At boundary of two air masses (cold and warm and moist) – In the USA, contrasting air masses often with temp differences of 20-30 C meet along a cold front. The flat land of the plains encourages rapid movement of the cold air as there is no friction at the surface which also means that the warm air is not cooled by adiabatic cooling as not forced to rise over mountain chains. This also leads to necessary wind shears to develop which begins rotation.
4. This creates instability and turbulence which creates supercell thunderstorms with large updrafts
5. These updrafts may start to rotate if there is high wind shear ie winds moving in different directions at different speeds – this creates a mesocyclone about 16km wide
6. With heavy rainfall from the cumulonimbus clouds that are formed, a rapid descending column of air may be dragged down to the ground which may then drag in warm moist air producing a storm wall cloud as it condenses
7. Cold air flows out which focuses the base whilst the updraft grows causing low pressure at the base at the surface. This creates the funnel cloud which reaches the surface.

Question 49

Tornado formation

Answer 49

1. Warm, moist air from Gulf of Mexico moving northwards meets cold air from the Rockies or Arctic air from Canada.
2. As the air descends as it passes over the Rockies it warms and starts to rise, this creates low pressure at the surface which causes more air to flow in from the surrounding area along a pressure gradient
3. As the landmass warms up during the day, the warm, moist air becomes unstable and lifts upwards through the cold air to form a small, low-pressure system called a mesocyclone.
4. Air from the surrounding area converges into the cyclone centre from high to low pressure and cumulonimbus clouds form with updraughts of warm air developing into a thunderstorm
5. The different wind speeds and directions between the warm and cold air masses results in vertical wind shears.
6. The converging air is deflected by the Coriolis force into a circular pattern and together with wind shears, results in air spinning upwards through the storm.
7. At higher levels, the jet stream must be fast at 65m/s to enable wind shears to develop high up and this jet stream also removes air at higher levels which maintains updraught allowing a fast inflow of air at the ground level.
8. Warm air continues to rise in the middle whilst cool air descends on the outer edge – this creates a supercell thunderstorm with a giant updraught along with heavy rain, hail, thunder and lightning.
9. Near the rear edge of the thunderstorm, tornadoes develop when the down-draughts of cold air create funnels which reach the ground.

Question 50

How are tornadoes measured?

Answer 50

Classified by their path length and width and wind speed. Fujita Intensity Scale classifies tornadoes based on an estimate from the damage they cause.

Question 51

Tornado wind hazard

Answer 51

High wind velocity – Within the tornado are rotating violent winds which may exceed 100m/sec and may reach 500km/h – faster than tropical cyclones Winds of 75 to 100 mph for F0 (120 to 180 km/h) Winds tend to spin anti-clockwise in northern hemisphere (& vice versa in southern hemisphere) despite being too small to be affected by Coriolis effect Remove and pick up objects – can injure or kill

Question 52

Tornado low pressure hazard

Answer 52

V. low pressure in centre (winds blow from high to low pressure along a pressure gradient which drops by 25mb per100m down to a pressure of 850mb in minutes- lower than a cyclone). (Compare with larger scale tropical cyclones which drop by 20mb per 100km.) The rapid change in pressure is very damaging – as a tornado passes over a building, the outside pressure is up to 200mb lower than the pressure inside causing buildings to undergo and explosive effect. People and animals can appear burnt by a tornado due to the rapid dehydration caused by the pressure fall.

Question 53

Tornado lifting force of funnel wall + intense ppt (rain + hail)

Answer 53

Can be considerable with reports of train carriages being lifted and moved hundreds of metres

Heavy rainfall / hail – risk of flash flooding but hail can actually damage homes eg mobile trailers

Question 54

Tornadoes prediction and warning

Answer 54

· Weather prediction technology has become so precise in recent years that tornadoes are almost always foreseen- a vast improvement in forecasting.
· 1980s, before the use of Doppler radar and other technologies, meteorologists were able to issue warnings just more than 50% of tornadoes
· In recent years, powerful tornadoes have been preceded by warnings 97 % of the time.
· Moreover, the rate of false warnings has been reduced from 73 to 24% with improvements in doppler and satellite technology
· However, unlike hurricanes, tornado warnings come with a much shorter lead time: around 15 to 18 minutes on average.
· And when tornadoes strike at night, as they did in Kentucky in December 2021 residents are more likely to miss the warnings. Tornadoes at night are 2.5 times as likely to result in fatalities..
· The F3 form in Kentucky had received Warnings the day before - reports by the national Storm Prediction Centre that tornadoes were quite likely.
· Others heard the warnings but chose not to act, being unsure that their neighbourhood would be affected – this is increasingly the case in a world with increasing risks from fires, floods etc where the public are suffering from information overload and fail to respond to warnings
· Nocturnal tornadoes are said to enhance vulnerability because they are difficult to spot and occur when the public tends to be asleep and in weak building structures.
· From 1950 to 2005, a mere 27% of tornadoes were nocturnal, yet 39% of tornado fatalities and 42% of killer tornado events occurred at night. Tornadoes during the overnight period are 2.5 times as likely to kill as those occurring during the daytime hours.
· This vulnerability is magnified when other factors such as increasing proportions of people living in mobile homes and an increasing and spreading population are realized. Nearly 61% of fatalities in mobile homes take place at night revealing this housing stock’s distinct nocturnal tornado vulnerability.
· Further, spatial analysis illustrates that the American South’s high nocturnal tornado risk is an important factor leading to the region’s high fatality rate.
· Even when warning systems are in place, the aged and children have higher mortality rates.

Question 55

Tornadoes Communicating the forecasts is crucial for community preparedness:

Answer 55

· NOAA Weather Radio may be purchased for $25-$100– daily forecasts showing areas likely to experience extreme weather.
· National weather radar network - improved from having no warning of threatening weather to about a 15-minute lead-time.
· Outdoor storm warning sirens in some areas and warnings issued by TV

Question 56

Tornadoes community preparedness

Answer 56

• In reality, an average of 60 people every year are killed by 1,200 tornadoes while 1,500 others suffer injuries. In addition, tornadoes cause roughly $400 million in damages, putting them on par with hurricanes.
• A tornado can strike quickly with little or no warning and may appear nearly transparent until the last minute – unlike hurricanes.
  Therefore….
  The only way for individuals to protect their lives and property from these unpredictable and devastating storms is through early education and preparedness training.
• Preparedness involves knowing the major dangers to avoid. However, only 20 states actively participate in community preparedness despite tornadoes being possible anywhere.
• Residents are advised to learn about the tornado warning system of their locality. Most tornado-prone areas have an outdoor siren system.
• Know how to distinguish between the siren’s warnings for a tornado watch and a tornado warning. Know that a watch means the conditions are right for a tornado to occur so listen out for advice, warnings are that one is occurring in the area
• Wireless Emergency Alerts (WEAs) are another method to stay up to date on weather emergencies. WEAs are emergency messages sent by authorized government authorities, such as the National Weather Service, through your mobile carrier. The alerts look like a text message and typically show the type and time of the alert, any action you should take, and the agency issuing the alert.
• Most states in the midwestern and southern United States conduct a state wide tornado drill in late winter or early spring in preparation for the severe weather season.

Question 57

Tornadoes landuse planning and hazard mapping

Answer 57

• Risk assessment carried out and development restricted or advised against eg avoid allowing mobile home parks in such areas FEMA produces:
• National Risk Index: a Tornado Risk Index score and rating represent a community’s relative risk for Tornados when compared to the rest of the United States.
• A Tornado Expected Annual Loss score and rating represent a community’s relative level of expected building and population loss each year due to Tornados when compared to the rest of the United States.
• Climate change is shifting the pattern making hazard mapping more difficult: Tornadoes, long associated with Oklahoma, Kansas and other sparsely populated Plains states, appear to be shifting eastward, occurring more frequently in states like Kentucky and Tennessee. And it’s putting more people at risk because the population density as you go east of the Mississippi River increases exponentially increasing the hazard risk.
• Although scientists lack the data to clearly connect tornadoes with climate change, a warming planet is producing more humid air near the Earth’s surface, which may in turn be fuelling more tornadoes, he said.

Question 58

Tornado hazard resistant design - preparedness

Answer 58

• Despite the success in prediction, as with all prediction and warning systems, community preparedness is important if the warnings are to be effective. People need to be aware of the threats and the safest place to be.
• It is not possible to modify the tornado event itself but hazard-resistant design can help to mitigate and reduce deaths by requiring solid construction of buildings and using basements as part of the structure to create ‘safe rooms’ – safe structure designed to comply with the Federal Emergency Management Agency criteria to provide near absolute complete protection – high probability of avoiding death from hurricanes and tornadoes
• Safe Rooms: First, the roof must be tightly secured to the walls, and the walls to the foundation, in order to transfer the pressure from the tornado downward to the strongest part of the building. Second, windows and other openings have to be strong enough to survive the debris, like tree limbs, that gets hurled through the air at high speeds during a tornado.
• However: Adding a safe room can cost from $7,000 for a house to as much as $100,000 for a version that holds about 100 people in a commercial building
• FEMA has tried to make these mandatory via building codes but they have been vetoed by housing developers because of the increased costs they will add to new builders - the cost benefit analysis concludes they are not cost effective due to their low incidence rate.
• Perception of risk affects response: States in Tornado Alley have no state-wide building codes. The National Association of Home Builders opposes even “safe rooms” on the basis of cost/benefit analysis .
• The probability/chance of any given location in Tornado Alley getting hit by an F-2 tornado (strong enough to do major structural damage) is about 1 in every 4,000-5,000 years; in other areas the annual probability is one in several million. The response has been less effective compared with hurricanes
• 3000 of them in Moore, Oklahoma where 55000 people live. Perception of risk and of state intervention and regulations by FEMA have limited willingness to install these, along with cost and hard ground which is difficult to dig into if installing retrospectively.
• 1999 – Moore – shelters worked in a tornado that killed dozens of people.
• Shelters for private houses are expensive – (2k-£3k) and there is an argument that the state should not invest its money – Midwesterners dislike state intervention (Republican voters – affects perception of risk) so, FEMA (Federal Emergency Management Agency) have a programme known as Sooner Safe – providing 75% of the cost to help people to increase the number and protection
• Poorer countries – less access to storm shelters, not enough for dense pops along vulnerable coastlines, These people also reluctant to leave their livestock so will not evacuate

Question 59

Tornado modify the loss after the event

Answer 59

• Tornado Insurance: In US, typical homeowner insurance policies include coverage for tornadoes . However, not everyone is covered and usually the poorest most vulnerable are not - 96% of US citizens have homeowners’ insurance
• Despite the high % of coverage, homes may be undervalued for insurance purposes

Question 60

Oklahoma, May 1999

Answer 60

Typical formation over Great Plains region – warm moist air from Gulf of Mexico, cool drier air on top from Canada and Rockies. This leads to instability. The layers do not mix as separated by a layer of warm dry air. Wind shear in upper levels is high and there is a clear frontal boundary between two contrasting air masses. Rotation occurs in jet stream. Does show that even in HIC with all the prediction and warning, some groups are worse affected and more vulnerable eg poor living in mobile homes which only 2% of which were affected but these housed 25% of the deaths

Scale:
- Swarm of 65 tornadoes along 150 mile belt from SW Oklahoma State towards Kansas
- Large tornado – 1-2km wide
- Tracked over 61km

Impacts:
- 45 people dead Widespread damage – 8000 buildings ruined or damaged
- First tornado to cause over £1billion worth of damage

Main Hazards:
- Winds up to 318mph – reached F5 on US based Fujita Scale – F4 and F5 tornadoes are rare and account for only 2% of US tornadoes but cause 66% of deaths – even following the guidelines and sheltering in a safe room may not save lives
- Lifted 22 homes off their foundations

Management:
Prediction and warnings:
- Storm Prediction Centre predicted small risk of tornadoes on 3 May but considered upper winds to be not strong enough for wind shear for them to develop – small changes in the atmosphere were missed by 100 weather balloons launched that morning.
- By mid-day – wind profiles (upward pointing radars) picked up increasing upper atmosphere winds and Storm Prediction centre gave warnings of strong risk of tornadoes - but not possible to say if and where they would strike.
- All of the storms were strong supercell thunderstorms and all produced tornadoes so risk even higher

• Death toll relatively low for a F5 , no deaths in 4-24 age group:
  Why? :
  · Tornadoes were huge, visible and audible
  · Local radio and TV gave huge coverage – NOAA radio broadcasts and people had signed up for free phone and email alerts
  · Warnings from the National Weather service gave average lead time of 32mins for Oklahoma City – twice the normal time · Warnings have improved with eth use of dopplar radar which detect wind changes
  · The Storm Prediction Centre gave early warnings – but not everyone takes notice of these as 75% are inaccurate

Preparation:
- Walls caved in, 20 homes lifted by lifting force of funnel wall, roofs blew off and 8000 buildings ruined or damaged – even buildings built to withstand 80mph winds could not withstand this
- Damage was widespread – at right angle stop the tornadoes’ paths as weak roofs were sucked into the vortex.
- Mobile homes most vulnerable – F1 overturns mobile homes but F2 demolishes them, Mobile homes here accounted of less than 2% of damaged structures but 25% of deaths were in these homes – poverty, social class and race determiners to vulnerability.

Question 61

Moore, Suburb of Oklahoma City 2013

Answer 61

Shows lessons learnt from 1999 and improved risk perception so people acted on warnings and so death toll low. Also shows that poverty and residential quality and vulnerability still not addressed in the USA despite wealth and lessons not learned from Oklahoma in 1999 and other hazards eg Hurricane Katrina.

Scale:
- F5
- Usually narrow track but this was an unusual wedge shape so damage greater
- 200mph wind
- Stayed on the ground for 45miutes prolonging impacts and track stretched 27 km long and 2 miles wide
- Hit densely populated suburb of Oklahoma City – Moore with population of 55,000 people

Impacts:
- 24 people dead
- Injured 237 and in total 10,000 people affected
- Plaza Tower Elementary and Briarwood Schools demolished – long term impacts on community and education
- Trailer parks worse affected eg on Highway 102 near Shawnee, Oklahoma
- Total cost: $2bn
- Homes destroyed: 2,500. Bridge destroyed (it crossed the Canadian River). Other buildings destroyed: cinema, bowling alley, Moore hospital etc
- Destruction to an oil production site= four oil tankers were blown away (one was found a mile away).

Main Hazards:
- High winds and hail hit Iowa and Kansas – hail as big as 10.8cm had destroyed the trailer park at Shawnee, Oklahoma

Management:
Prediction:
- Only 16 minutes warning time and whilst many people usually do not heed warnings (because 75% are found to never happen) , it is likely that they did in this area since they had suffered a devastating tornado swarm in 1999 so their perception of risk was heightened since their experience was in living memory

Question 62

Jiangsu, China 2016

Answer 62

Contrast with Moore – lack of explicit overall watch and warning system and no building design preparation

Scale:
- F4.
- Why? Late spring & early summer, a semi permanent frontal boundary emerges across eastern China. This leads to prolonged rainfall and thunderstorms.
*Rainfall along this boundary tends to be particularly heavy in post El-Nino summers e.g., Summer of 2016. On June 23, a band of intense thunderstorms hit eastern China.
- One storm complex over Jiangsu province spanned 400km and produced a tornado.
- Wind speeds= up to 322 km/h
- Hailstones (20-50 mm) in diameter (the hailstorms caused destruction to homes, shops and commercial buildings).
*Similar to the Moore tornado- it was wedge-shaped (this resulted in a wide path of destruction).
- Secondary hazard= flooding

Impacts:
- Death= 99 and 846 injured.
- US$760million
- Damage: thousands of brick homes were destroyed (many were completely leveled); manufacturing plants; businesses and rice mills were also destroyed. Additionally, multiple large factory buildings were severely damaged at a Canadian Solar plant and a large school building sustained severe damage. Many vehicles were tossed and destroyed; trees were completely uprooted and metal power line pylons.
- In total= 3,200 homes were destroyed.
- Power and telephone communications were knocked out over a broad area and roads were blocked.
**According to Greenpeace- the tornado substantially damaged a hazardous chemical storage warehouse that stored large quantities of hazardous chemicals (including: hydrofluoric acid, hydrogen chloride, ammonia and sulphuric acid). = Significant impacts to public health and the local ecosystem.

Main Hazards - Winds and hail

Management:
Before – prediction
- Similar Dopplar radar to National Weather Service – limited time to predict as first indication appeared on radar about 30 minutes before the tornado formed.
**Weaknesses= Although China is vulnerable to tornadoes, they do not have an explicit watch or warning system. Instead, forecasters may opt to mention the possibility of a tornado. In this instance though, the real-time nowcast and warning services in this event were quite successful for the severe weather hazards but understated the tornado risk. Automated software detected a potential tornado, and forecasters made a nowcast at 2:30 pm acknowledging the potential for an F2 tornado within two hours. By this point, the tornado had already been on the ground for 20 minutes. Finally, the possibility of a developing tornado was noted in a subsequent bulletin at 2:40 pm, more than halfway through the tornado’s 50-minute lifespan.
- Preparation *Building regulations do not combat tornadoes= not tornado hazard proof (vs USA with its safe rooms).

After
* The event was declared a national level disaster.
* Disaster response teams were deployed from Beijing that evening providing: 1,000 tents; 2,000 beds and floodlights to aid the rescue efforts. Food and water were also delivered.
*More than 1,300 police officers were mobilised to help.
- The China Meteorological Administration has now embarked on a program to develop an improved tornado reporting system and is testing new methods of monitoring and warning

Question 63

Describe the relationship between the number of tornadoes and the number of tornado-related deaths shown in Fig. 7.1 (3)
Suggest reasons for the relationship you described (7)

Question 64

Describe the pattern of trends in frequency of tornadoes shown in Fig. 7.1 (4)
Explain why the location of tornadoes varies (6)

Answer 64

Question 65

Describe the pattern of tornadoes shown in Fig. 7.1 (4)
Suggest reasons for the pattern of tornadoes just described (6)

Answer 65