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Weather Hazards


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?

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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.



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 daysor 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.

Short-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 byHurricane Katrina. Thisis a long-term effect of a weather hazard.

Long-term effects of weather hazards


Short-term and long-term effects






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How do hurricanes form?


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

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 surge8.5 metres high. New Orleans

Hurricane Katrina


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

At first New Orleansseemed to have weathered the worst of thehurricane,but laterstorm surgesbreachedthe city’s

protective levees.

Hurricane Katrina’s effects


80% of the city was flooded and over a million homes were left without electricity.Over 1,800 deaths werecaused by the storm, around700 of them in New Orleans.

In some areas the flood level rose to over six metres. Thosethat had decided to stay in theirhomes had to either find highground and await rescue or risk swimming and wadingthrough polluted floodwater.



The storm forced over a million people to leave their homes. Italso 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.



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?

Dealing with Hurricane Katrina


Decide the alert level


Hurricane Katrina news report






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Although hurricanes may be larger in size, the winds inside a tornado are far more concentrated. This givesthem 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).

Tornados are one of nature’s most powerful forces.

Tornados


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

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).

Tornado formation


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

>15Tornado Alley

Where do tornados occur?


Tornado Alley in the USA is particularly prone to tornados asit is where cool, dry air moving southwards from Canada, collides with warm, humid tropical air movingnorthwards from the Gulf of Mexico.

The tornado season in the USA generally lasts from Marchuntil August.

When the cold front and the warmfront meet, the combination ofwarm rising air and cold falling air is exactly right for tornado formation.

Tornado Alley


Classifying tornados





What are the causes, effects and dangers from other weather hazards?

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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.

Heatwaves


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

European heatwaves


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

However, forest firesnot only harm humans andanimals, they can also burnaway much of the vegetationthat prevents erosion. This cansometimes result in landslides.

Forest fires

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http://www.sxc.hu/browse.phtml?f=download&id=204085


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 environmenthighly 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.

Why do forest fires start?


As human developmentencroaches further into areasof 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.

Human activity and carelessness cause the greatest numberof forest fires, however fires caused by lightning tend to burnfar larger areas, as often these occur in remote places and itmay be some time before fire-fighters are aware of them.

Humans and forest fires


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 sanitationand the pollution of water sources.

Drought


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

Constructing dams mayseverely affect the courseof a river, causing it to dryup further downstream.

Deforestation (the removalof forests) can dramaticallyalter the soil’s ability to hold

water, drying out the groundand triggering desertification.

Human activities and drought


Match the definitions


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.

Lightning effects


Why does lightning occur


A lightening bolt containson average over 300 million volts and can raise the air temperature around it to27,700°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.

Lightning facts


How does hail form?


Hailstorms can devastate crops and cause extensivedamage. On rare occasions, hailstones have grownso large that their impacts have had fatal consequences.

The heaviest hailstone ever recorded hada mass of over one kilogram and fell duringa storm inIndia that killed 92 people.

Hailstorm effects


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 floodat 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.

Flooding


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

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

Dykes and levees act as flood barriers along major rivers. Dams make it possibleto control the amount ofwater flowing through a river.

Flood defences


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 benefitsas 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 asponge, which prevents flooding elsewhere.

Flood plains and wetlands


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

Human impact on flooding


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

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

Blizzards


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.

White-out


Weather hazards bingo


Hurricanes form out at sea, when warm ocean air risesupwards 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 overan extended period for a certain region.

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

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

Key ideas


Lightning is an electrostatic discharge which occurs withina 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.

Key ideas

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