Extreme Weather Example Severe Thunderstorms

Extreme Weather

Extreme weather is when a weather event is significantly different from the average or usual weather pattern. This may take place over one day or a period of time. Flash floods, heat waves, thunderstorms and cyclones are examples of extreme weather.

Starter

Brainstorm types of extreme weather. From your list, work out the likely chance of being caught in each of these weather events. Use a ranking scale of 1 (Very Likely) to 4 (Very Unlikely).

Extreme weather example – ‘Severe Thunderstorms’

The following information has been taken and edited from: http://www.bom.gov.au/info/thunder/

1. THE IMPACT OF SEVERE THUNDERSTORMS

Severe thunderstorms are localised events, usually affecting smaller areas than tropical cyclones and floods, so their devastating impact is often underestimated. These storms, which are more common than any other natural hazard, can occur anywhere in Australia. Each year, on average, severe thunderstorms are responsible for more damage (as measured by insurance costs) than tropical cyclones, earthquakes, floods or bushfires. Unfortunately, thunderstorms also kill people - between 5 and 10 deaths are caused by lightning strikes each year. More deaths occur when strong winds cause tree limbs to fall, debris to become projectiles and small boats in open water to capsize. Although many people believe that tornadoes do not occur in Australia, they have caused at least 41 deaths here.

2. SEVERE THUNDERSTORMS: DEFINITION, CAUSES AND OCCURRENCE

A severe thunderstorm is defined by the Bureau of Meteorology as one which produces:

 hail, diameter of 2 cm or more ($2 coin size); or

 wind gusts of 90 km/h or greater; or

 flash floods; or

 tornadoes, or any combination of these.

Most thunderstorms do not reach the level of intensity needed to produce these dangerous phenomena, but they all produce lightning which can cause death, injury and damage.

Lightning and Thunder - Lightning is the discharge produced when voltage differences between ground and atmospheric electrical charge are large enough (several hundred million volts) to overcome the insulating effect of the air. Strokes can occur within the cloud, between clouds, or between clouds and the ground. Thunder is the sound produced by the explosive expansion of air heated by the lightning stroke to temperatures as high as 30,000°C.

Hail - Hailstones can form in a thunderstorm with a strong updraught when frozen raindrops, 'suspended' in the updraught, grow rapidly by 'sweeping up' small cloud droplets which freeze on contact. Hailstones larger than cricket balls have been recorded in Australia (eg Sydney, April 1999). Wind Gusts - In a mature thunderstorm, the falling rain and hail drag the surrounding air downwards. In addition, evaporation from the raindrops cools the nearby air, accelerating the downward rush. This strong downdraught spreads out upon reaching the ground, producing a cool, gusty wind that can cause damage.

Flash Floods - The updraught of a mature thunderstorm produces raindrops by the condensation of moist air that cools as it rises. When the raindrops become too large to be supported they fall, but the intense updraught of a severe thunderstorm can suspend huge amounts of rain before releasing a deluge. Such rain can reach intensities of more than 200 mm/h, provided the environment is humid enough to feed the thunderstorm with enough moisture. Flash floods often result when the thunderstorm moves slowly, so that a small area receives most of the rain, but the drainage and run-off characteristics on the ground can also determine the area of greatest impact.

Tornadoes - These rarest and most violent of thunderstorm phenomena are rapidly rotating columns of air that descend in the well- known funnel shape from the base of a storm cloud. A tornado vortex, which can range in width from a few metres to hundreds of metres, usually whirls clockwise (viewed from above) and contains very damaging winds that may reach more than 450 km/h. Photo 8 shows tornado tree damage, while 9 & 10 are tornadoes at Tarlee, SA, & Northam, WA respectively.

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Case Study - Australian Severe Weather: Cyclone Yasi

Research sources

The following information has been taken and edited from: BBC news report written on Feb 2, 2011 - http://www.bbc.co.uk/news/world-asia-pacific-12342031 Queensland government website - http://www.derm.qld.gov.au/parks_and_forests/cyclone-yasi.html

When and where did it occur?

Fierce winds and driving rains brought by the most powerful storm ever to hit Queensland are lashing northern coastal areas of the Australian state. Cyclone Yasi made landfall between Innisfail and Cardwell at around midnight local time on February 2, 2011. The eye of the storm was reported to be 35km (22 miles) in width, with a front stretching across 650km (400 miles). What caused it?

BBC meteorologist, Holly Green, provides this explanation:

“ There are lots of ingredients needed to develop a tropical storm including heat, moisture and falling surface pressure. All these factors have come together this time to create a powerful storm. Yasi developed into a severe tropical cyclone as it tracked across the Coral Sea and large amounts of very warm, moist air were drawn into the system, giving it a great deal of energy. There have been seven tropical cyclones in the vicinity of Australia, New Zealand and Fiji in the past three weeks. This is unusual and possibly linked with the strong La Nina weather pattern.”

What were the impacts on people?

With winds reaching up to 290km/h (181mph), Cyclone Yasi is ripping roofs off buildings and has cut power to at least 100,000 people. The storm struck south of Cairns and is moving inland, with forecasters warning of severe damage and likely deaths. Queensland's premier has warned of devastation on an unprecedented scale.

'Destroyed'

The town of Tully, close to where the cyclone hit land, is a "scene of mass devastation", resident Ross Sorbello told the Sydney Morning Herald. Mr Sorbello, who briefly went outside as the eye of the storm passed over, said roofs were ripped from houses, electricity poles were down and the streets were covered with debris. Tully resident Stephanie Grimaz said that houses in her street had been torn apart, the Queensland Times reported.

"The flat from across the street is in our front yard and we can see other houses which have just been destroyed," she said.

Other eye-witness reports

"We couldn't get any tape for our windows so we tried to use wide sticky tape but it's peeling off... we are very scared. One side of our whole house is just glass," she told ABC News.

"We are actually camping under a desk that is bolted to concrete walls on two sides."

Those remaining in their homes were told to tape up windows, fill sandbags and prepare a "safe room" with mattresses, pillows, a radio, food and water supplies to wait out the cyclone. They were also encouraged to fill bathtubs with water for drinking supplies. Cairns resident Philip Baker told the BBC it seemed "a safer bet" to stay in his home rather than flee or head to an overcrowded evacuation centre with his wife and young daughter.

The nearby communities of Mission Beach and Innisfail are also believed to be badly affected. Officials say the full extent of the damage will not be known until daybreak. More than 10,000 people are in evacuation centres, which became so overcrowded that people were turned away.

What were the impacts on environment?

Other residents of Tully described tree tops being shredded by winds that roared like jet engines, and water being forced under doors by the pressure.

Impacts on parks and forests

The parks and forests within the cyclone’s path suffered extensive damage with tree falls; loss of branches, epiphytes and vines; and leaf stripping of the canopy. As part of Queensland Parks and Wildlife Service’s (QPWS) disaster response, rangers from around the state were quickly mobilised to begin the immense task of reopening parks. Find out more about the QPWS cyclone response. An immediate concern was the damage to the rainforest habitat of the endangered southern cassowary. Loss of canopy fruit resources has caused a severe food shortage for the cassowary population that will last for months after the cyclone. Find out more about the QPWS Cassowary Response Team.

The cyclone also caused severe damage to important habitat for endangered mahogany gliders. These elusive gliders live in a fragmented strip of lowland sclerophyll forest between Townsville and Tully. Find out more about the QPWS mahogany glider disaster response strategy.

What was the extent (scale) of the hazard?

Yasi was classed as a category five cyclone as it crossed the coast - the highest grade in the scale used to measure such storms. The Australian Bureau of Meteorology later downgraded the storm to category four and then to category three, but still classified it as dangerous. State Premier Anna Bligh described the weather system as the "most catastrophic storm ever seen" in the state. She warned that it could cause a tidal surge as high as 9m (nearly 30ft) in some places, overwhelming low-lying coastal areas.

"It will take all of us and all of our strength to overcome this. The next 24 hours I think are going to be very, very tough ones for everybody," she told a news briefing.

Prime Minister Julia Gillard described the storm as a "cyclone of savagery and intensity".

The state disaster co-ordinator, Ian Stewart, warned residents they would be on their own during the coming hours as it was too dangerous to send out emergency workers. Many fear that Yasi could be worse than Cyclone Tracy, which hit Darwin on Christmas Eve in 1974 and killed 71 people. That was a category four storm. The cyclone follows the worst floods in Queensland's history, triggered by tropical storms which have battered the region since the end of November.

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Research Task – Severe weather case study

Select a type of severe weather to research. Collect background information and create a case study report including the following information:

• Include a world map that shows the global distribution of this type of extreme weather

• Write an explanation for this type of extreme weather

• Obtain information on the frequency and severity of this type of extreme weather

• Amazing facts on this type of extreme weather hazard (List using a table)

Research one example of this type of hazard that has occurred in the last decade:

 When and where did it occur?

 What caused it?

 What was the extent (scale) of the hazard?

 What were the impacts on people?

 What were the impacts on environment?

 What is the history of this type of extreme weather at this location?  How prepared were the people at this location?

 Explain and evaluate how the local community responded to this extreme weather event.

 Include some images of the impacts of this extreme weather on the environment and on people.