What is a weather hazard? • What are the causes and effects of hurricanes? • What are the causes and effects of tornados? • What are the causes, effects and dangers of other weather hazards? • Summary activities The key concepts covered are: Place, Space, and Physical and human processes.
What is a weather hazard? By the end of this section, you will: • Know what is meant by the term weather hazard. • Be able to name some types of weather hazard. • Understand what some of the short-term and long-term effects of weather hazards are.
What is a weather hazard? A weather hazard is any naturally occurring weather condition that has the potential to cause harm or damage, such as: • hurricanes • tornadoes • white-outs • forest fires. By understanding weather hazards we can minimize the damage they cause. The effect of weather hazards can be felt for a short time or they can be more permanent.
In the short-term Short-term effects will normally only last a few days or weeks. They will not cause any lasting or permanent damage. Examples may include: • slight damage to land and/or buildings • temporary migration of the population • a disruption to power supplies. Can you think of any other short-term effects that might arise?
The long run Long-term effects can include large-scale destruction of property, or a complete alteration of the physical landscape. These pictures show the Chandeleur islands in the USA before and after Hurricane Katrina. As you can see, their geography has been permanently altered by the hurricane. Can you think of any other long-term effects that might arise?
What are the causes and effects of hurricanes? By the end of this section, you will: • Know how hurricanes are formed and why they cause so much damage. • Understand more about the devastation that was caused by Hurricane Katrina.
Hurricane Katrina Hurricane Katrina was the most powerful hurricane to hit the USA in known history. It hit New Orleans on the morning of the 29th August 2005 bringing with it terrible destruction. New Orleans Winds of over 250 kilometres per hour were recorded as Katrina hit the coast, causing a storm surge 8.5 metres high.
Devastation At first New Orleans seemed to have weathered the worst of the hurricane, but later storm surges breached the city’s protective levees. People that had not left their properties were stranded and had to wait to be rescued or wade through polluted floodwater. It was a hugely devastating natural disaster.
The aftermath How badly did Hurricane Katrina affect New Orleans? • Flood levels were over six metreshigh. • 80% of the city was flooded. • Over a million homes were left without electricity. • There were700 deaths in New Orleans. • Over a million people had to leave their homes. • Damaged oil refineries spilt 24 million litres of crude oil. • Over $81 billion worth of damage was done.
What are the causes and effects of tornadoes? By the end of this section, you will: • Know what a tornado is and how it is formed. • Know what Tornado Alley is and why tornadoes are found there. • Understand what the Fujita scale is and why it is used.
Tornado 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. Powerful tornados have produced wind speeds of over 500kmph – about double those of Hurricane Katrina.
How do tornados form? 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. If this spinning vortex, known as a funnel cloud, has enough energy, it grows larger until it eventually hits the ground, forming a tornado.
Tornado Alley Tornados occur all over the world but a large percentage of them form in an area of the USA known as Tornado Alley. Tornado Alley Can you identify Tornado Alley on this map?
Why here? Tornado Alley 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 warmfront meet, the combination ofwarm rising air and cold falling air is exactly right for tornado formation. The tornado season in the USA generally lasts from Marchuntil August.
What are the causes, effects and dangers of other weather hazards? By the end of this section, you will: • Know the causes and effects of more weather hazards. • See the impact that flooding has on different places. • Have formed your opinion on whether human activities contribute to weather hazards.
Floods Flooding is the most frequently occurring disaster in the world. Flooding occurs when rivers cannot contain their waters and overflow. It can also occur when storms at sea drive large amounts of water onto the coast and past flood defences. Heavy rain concentrated in a local area can cause water levels to rise sharply which may result in a flash flood. Can you think of any floods that have happened in the recent past?
Money flooding in? Gordon Brown promised £46 million in aid to flood-hit councils and an £800 million rise in annual spending on flood protection by 2010-11. “Some villages and communities have now been totally wiped off the map of Ghana.” George Azi Amoo - Ghana's national disaster management co-ordinator What do the different responses to the floods tell us about these countries?
Defending ourselves To combat the dangers of flooding, humans have built many different 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 coastal defences can help protect shorelines from sea-flooding. The Thames barrier is a floating barrierwhich can close to protect London from sudden tidal surges.
Flood plains and wetlands Flooding is an natural event that can never be fully controlled. Wetlands and flood plains contain life that has specially adapted to deal with flooding. These areas also act as flood defences, soaking up water like a sponge. This prevents flooding elsewhere. Flooding can bring natural benefits to many areas. The mineral rich nutrients that it spreads make soil fertile.
Human impact Building on flood plains dramatically increases the risk of flooding disasters. Water runs off tarmac. As a result, it cannot be absorbed by the earth. Human actions have added to the devastation floods can cause. Dams and flood defences disturb the natural flow of water. Although dams offer protection to some areas, they may cause flooding elsewhere.
Human activities Constructing dams may also severely affect the course of a river, causing it to dry up further downstream. This could possibly result in a drought affecting a region. Deforestationcan alter the soil’s ability to hold water, drying out the ground and triggeringdesertification. Do you think humans actions have had an impact on the destructive nature of weather hazards?
Summary activities By the end of this section, you will: • Be confident in your knowledge of what weather hazards are. • Know how to use and spell important terminology relating to weather hazards.