Weather Hazards

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This icon indicates that the slide contains activities created in Flash. These activities are not editable. For more detailed instructions, see the Getting Started presentation. 1 of 45 © Boardworks Ltd 2006 What is a weather hazard? What are the causes and effects of massive hurricanes, such as Hurricane Katrina? What are the causes and effects of tornados? What are the causes, effects and dangers of

other weather hazards? Learning objectives Learning

2 of 45 © Boardworks Ltd 2006 What is a weather hazard?

A weather hazard is any naturally occurring weather condition that has the potential to cause either harm or damage.

We need to understand weather hazards so that we can minimize the risk to human life.

Weather hazards can have short-term and long-term effects.

3 of 45 © Boardworks Ltd 2006 Short-term effects of weather hazards

Short-term effects might include superficial damage to land and buildings or a temporary population migration from an area. Food sources, power lines and supply routes may also be temporarily damaged by any number of weather hazards.

Short-term effects will only last a few days or weeks. They will not cause any lasting changes to the ecosystem, the population or the ecology of the land. Not being able to go to school due to too much ice or snow on the roads would be a short-term effect of a weather hazard.

4 of 45 © Boardworks Ltd 2006 Long-term effects of weather hazards

Long-term effects can include large-scale destruction of property, or a complete alteration of the physical landscape. Some weather hazards may permanently alter the ecosystem through habitat destruction, which can have knock on effects for many species. This picture shows the Chandeleur islands in the USA, which have had their geography, permanently altered by Hurricane Katrina. This is a long-term effect of a weather hazard.

5 of 45 © Boardworks Ltd 2006 Short-term and long-term effects

6 of 45 © Boardworks Ltd 2006 What is a weather hazard? What are the causes and effects of massive hurricanes, such as Hurricane Katrina? What are the causes and effects of tornados? What are the causes, effects and dangers of

other weather hazards? Learning objectives Learning

7 of 45 © Boardworks Ltd 2006 How do hurricanes form?

8 of 45 © Boardworks Ltd 2006 Hurricane Katrina

Hurricane Katrina was the most powerful hurricane to hit the United States in known history.

9 of 45 © Boardworks Ltd 2006 Hurricane Katrina

Hurricane Katrina hit New Orleans on the morning of the 29th August 2005 bringing with it terrible destruction.

Winds of over 250 kilometres per hour were recorded as Katrina hit the coast, causing a storm surge 8.5 metres high. New Orleans

10 of 45 © Boardworks Ltd 2006 Hurricane Katrina’s effects

At first New Orleans seemed to have weathered the worst of the hurricane, but later storm surges breached the city’s protective levees.

The levees are walls and embankments built alongside the rivers to keep New Orleans safe from flooding.

11 of 45 © Boardworks Ltd 2006 Hurricane Katrina’s effects

80% of the city was flooded and over a million homes were left without electricity. Over 1,800 deaths were caused by the storm, around 700 of them in New Orleans. In some areas the flood level rose to over six metres. Those that had decided to stay in their homes had to either find high ground and await rescue or risk swimming and wading through polluted floodwater.

12 of 45 © Boardworks Ltd 2006 Hurricane Katrina’s effects

The storm forced over a million people to leave their homes. It also damaged oil refineries, spilling 24 million litres of crude oil. In total, Hurricane Katrina caused over $81 billion worth of damage, making it the costliest Atlantic hurricane ever.

Much of the damage is still being felt. In June 2006, the population of New Orleans was only about half what it had been before the hurricane and repairs on the levee system were still unfinished.

13 of 45 © Boardworks Ltd 2006 Dealing with Hurricane Katrina

For the mayor of New Orleans, Ray Nagin, Hurricane Katrina was the greatest challenge he had ever faced.

Imagine yourself in his position– you need to prepare the city as best you can, monitor the defences and communicate effectively with state and national organizations and coordinate a relief effort during a time of great crisis.

Which part of this job would you find the most stressful?

14 of 45 © Boardworks Ltd 2006 Decide the alert level

15 of 45 © Boardworks Ltd 2006 Hurricane Katrina news report

16 of 45 © Boardworks Ltd 2006 What is a weather hazard? What are the causes and effects of massive hurricanes, such as Hurricane Katrina? What are the causes and effects of tornados? What are the causes, effects and dangers of

other weather hazards? Learning objectives Learning

17 of 45 © Boardworks Ltd 2006 Tornados

Tornados are one of nature’s most powerful forces.

Although hurricanes may be larger in size, the winds inside a tornado are far more concentrated. This gives them the power to cause extreme devastation wherever they hit. Powerful tornados have produced wind speeds of over 500 kmph, (about double those of Hurricane Katrina).

18 of 45 © Boardworks Ltd 2006 Tornado formation

Tornados form where there is warm air rising upwards from the ground. If this rising, warm air then collides with the descending cool air of an oncoming thunderstorm, it can produce a spinning vortex (similar to the vortex you see when you take the plug out of the bath).

If this spinning vortex, known as a funnel cloud, has enough energy, it grows larger until it eventually hits the ground, forming a tornado.

19 of 45 © Boardworks Ltd 2006 Where do tornados occur?

Tornados occur all over the world but a large percentage of them form in an area of the USA known as Tornado Alley.

Tornados per year

<1 1–5 6–10 11–15 >15 Tornado Alley

20 of 45 © Boardworks Ltd 2006 Tornado Alley

Tornado Alley in the USA is particularly prone to tornados as it is where cool, dry air moving southwards from Canada, collides with warm, humid tropical air moving northwards from the Gulf of Mexico. When the cold front and the warm front meet, the combination of warm rising air and cold falling air is exactly right for tornado formation. The tornado season in the USA generally lasts from March until August.

21 of 45 © Boardworks Ltd 2006 Classifying tornados

22 of 45 © Boardworks Ltd 2006 What is a weather hazard? What are the causes and effects of massive hurricanes, such as Hurricane Katrina? What are the causes and effects of tornados? What are the causes, effects and

dangers from other weather hazards? Learning objectives Learning

23 of 45 © Boardworks Ltd 2006 Heatwaves

A heatwave is when a region experiences a prolonged period of unusually hot weather. A heatwave in Britain may only reach temperatures considered normal for other areas of the world, but it will still be classed as a heatwave because it exceeds that region’s normal temperatures.

24 of 45 © Boardworks Ltd 2006 European heatwaves

In August 2003, Europe suffered one of the most extreme heatwaves of recent time. Temperatures in France soared to up to 40°C. Over 50,00 people died from the effects of the heat, nearly 15,000 of them in France. There were also shortfalls in crop production due to drought.

25 of 45 © Boardworks Ltd 2006 Forest fires

Extreme heat can also bring with it the danger of fire. Forest fire has been recognized as a natural part of the ecosystem, with many plants and trees requiring fire for germination of their seeds. The eucalyptus tree even has flammable oil in its leaves to encourage fire. Fire gives this tree an advantage over its competitors as it is faster at re-growing.

However, forest fires not only harm humans and animals, they can also burn away much of the vegetation that prevents erosion. This can sometimes result in landslides.

26 of 45 © Boardworks Ltd 2006 Why do forest fires start?

Forest fires start when there is little rain and a lot of heat. This dries out the soil, which causes the plants to release ethylene, a flammable gas. The combination of this and a lot of dry fuel on the forest floor, makes the environment highly flammable.

Some fires can start through spontaneous combustion - materials like hay and tree resin will catch fire if sufficiently heated. However, lightening and human carelessness cause most forest fires.

27 of 45 © Boardworks Ltd 2006 Humans and forest fires

Human activity and carelessness cause the greatest number of forest fires, however fires caused by lightning tend to burn far larger areas, as often these occur in remote places and it may be some time before fire-fighters are aware of them. As human development encroaches further into areas of wild vegetation, the risk to human life becomes far greater. In recent years, cities like Sydney, Australia and populated areas in southern California have all suffered great damage due to large forest fires.

28 of 45 © Boardworks Ltd 2006 Drought

Perhaps the most potentially dangerous weather hazard to human life, is long-term drought. Like heatwaves, there may be relative differences in drought conditions from region to region, but all droughts result from lack of available water. Without water, crops fail and animals die, so droughts are often followed by famines.

Disease is also prevalent during droughts due to a lack of sanitation and the pollution of water sources.

29 of 45 © Boardworks Ltd 2006 Human activities and drought

Droughts are not just the result of weather conditions. Human actions can also cause droughts.

Constructing dams may severely affect the course of a river, causing it to dry up further downstream.

Deforestation (the removal of forests) can dramatically alter the soil’s ability to hold water, drying out the ground and triggering desertification.

30 of 45 © Boardworks Ltd 2006 Match the definitions

31 of 45 © Boardworks Ltd 2006 Lightning effects

It is thought that lightning strikes occur 100 times every second. Most of these strikes only happen within storm clouds and never reach Earth, but those that do can be very dangerous. One estimate suggests that over 2,000 people die each year from lightning, but with many strikes unreported or occurring in remote areas, it is hard to gauge the real number. Central Africa has the highest rate of lightning strikes per year.

32 of 45 © Boardworks Ltd 2006 Why does lightning occur

33 of 45 © Boardworks Ltd 2006 Lightning facts

A lightening bolt contains on average over 300 million volts and can raise the air temperature around it to 27,700°C, (about 5 times that of the surface temperature of the sun).

Lightning also moves more than 15,000 times faster than a bullet with the average length of a lightning streak being around six miles long.

Hailstorms can devastate crops and cause extensive damage. On rare occasions, hailstones have grown so large that their impacts have had fatal consequences.

The heaviest hailstone ever recorded had a mass of over one kilogram and fell during a storm in India that killed 92 people.

Flooding is the most frequently occurring disaster in the world today. Heavy rain concentrated in a local area can cause water levels to rise sharply which may result in a flash flood. Flash floods arise quickly with little advance warning, like the flood at Boscastle, England in 2004. Flooding occurs when rivers cannot contain their waters and overflow. Flooding can also occur when storms at sea drive large amounts of water onto the coast which can surge past flood defences.

To combat the dangers of flooding, humans have built a variety of flood defences.

Dykes and levees act as flood barriers along major rivers. Dams make it possible to control the amount of water flowing through a river.

Sea walls and costal defences can help protect shorelines from sea-flooding. The Thames barrier is a floating barrier which can close to protect London from sudden tidal surges.

Although flood defences can minimize the danger from flooding to certain areas, flooding is an natural event that can never be fully controlled. In many parts of the world, flooding brings great benefits as it spreads mineral-rich silt and nutrients over the land, making the soil very fertile. Wetlands and flood plains contain animal and plant life specially adapted to deal with flooding. These areas also act as flood defences, soaking up lots of water like a sponge, which prevents flooding elsewhere.

Building roads and houses on flood plains dramatically increases the risk of flooding disasters. Water simply runs off tarmac and concrete and continues on its journey to more populated areas, without being absorbed into the ground.

Dams and flood defences also disturb the natural flow of water. Although dams offer protection to some areas, they may inadvertently cause flooding elsewhere.

A blizzard is an extreme winter storm, which is characterized by strong winds, decreased visibility, freezing temperatures and falling snow or ice.

The decreased visibility in blizzards causes many accidents. For anyone trapped or injured in a blizzard, the risk of hypothermia is very severe.

The most extreme form of blizzard is known as a white-out. This is when the snow is so heavy that it becomes impossible to distinguish the ground from the air.

People easily become lost and disorientated in these very dangerous conditions. Car accidents are common and aeroplane pilots caught in these conditions, may have difficulty in keeping a steady altitude.

Hurricanes form out at sea, when warm ocean air rises upwards to create a cycle of evaporation and condensation.

Tornados occur when warm fronts collide with cold fronts, forming a vortex or funnel cloud which then hits the ground.

Heatwaves are when the temperature is unusually high over an extended period for a certain region.

Forest fires are mainly caused by human activity but are also caused by lightning. Drier conditions increase the risk of fire.

Droughts are extended periods when water availability falls below the statistical requirements for a region.

Lightning is an electrostatic discharge which occurs within a cloud, or strikes from a cloud to the Earth.

Hail forms when ice crystals gather moisture and refreeze over and over again, until heavy enough to fall to Earth.

Floods are an overflow of water that submerges land. They vary in severity and may occur for many different reasons.

Blizzards are extreme winter storms, characterized by strong winds, freezing temperatures and decreased visibility.