Hurricanes

The strongest tropical storms are called hurricanes, typhoons or tropical cyclones. The different names all mean the same thing, but are used in different parts of the world. If these huge storms start in the Atlantic off the west coast of Africa, they are called hurricanes.

In an average year over a dozen hurricanes form over the Atlantic Ocean and head westwards towards the Caribbean, the east coast of Central America and the southern USA (Florida in particular). Hurricanes may last as long as a month, and although they travel very slowly, usually about 24 km/h (15 mph) – wind speeds can reach over 120 mk/h (75 mph).

Map showing route of hurricane Mitch, 1998

How hurricanes form

Hurricanes need a lot of heat to form (a sea surface temperature of at least 26 degrees), which is why they usually occur over tropical seas. They also need to be between 5 and 20 degrees north or south of the equator. It works like this:

• Rising warm air rises fast, causing towering clouds, heavy rainfall, and intense low pressure.
• The low pressure sucks in air, causing very strong winds which spiral - anti-clockwise in the northern hemisphere - around the centre of the low, at speeds of around 120 km/h (75 mph).
• Seen from above hurricanes are huge circular bodies of thick cloud around 450 km (300miles) wide. The cloud brings heavy rain, thunder and lightning.
• In the centre is the eye of the hurricane, about 45 km across (30miles) across. Often there will be no cloud in the eye. Seen from below it will seem calmer, with a circle of blue sky above. The eye is formed because this is the only part of the hurricane where air is sinking.
• In the northern hemisphere, the prevailing easterly tropical winds tend to steer hurricanes toward land - although their course is unpredictable. As they move inshore their power gradually reduces, because their energy comes from sucking up moist sea air.

Cross section diagram of a hurricane

Effects of tropical storms

The intense winds of tropical storms can destroy whole communities, buildings and communication networks. As well as their own destructive energy, the winds generate abnormally high waves and tidal surges, which cause flooding in coastal areas. The most destructive elements are the high seas and the flooding that accompany the storms.

MEDCsMEDC: A More Economically Developed Country [MEDC] has high levels of development, based on economic indicators, such as gross domestic product (the country's income). More of the countries in the northern hemisphere are MEDCs, eg UK, USA, Canada, Europe. More of the countries in the southern hemisphere are Less Economically Developed Countries [LEDCs]. are better placed to reduce the effects of tropical storms, because they have more financial resources and educational and technological know-how to help deal with them. This means they are better able to observe and predict storm behaviour, and to invest in infrastructure, which can withstand storms - as well as having more resources for repairing the damage caused.

Preparation and prediction

Techniques can be very different in MEDCs and LEDCs

Bangladeshi villager affected by cyclone Sidr

MEDCsMEDC: A More Economically Developed Country [MEDC] has high levels of development, based on economic indicators, such as gross domestic product (the country's income). More of the countries in the northern hemisphere are MEDCs, eg UK, USA, Canada, Europe. More of the countries in the southern hemisphere are Less Economically Developed Countries [LEDCs]. have the resources, and technology to predict and monitor the occurrence of storms, eg using satellites and specially equipped aircraft, to train the emergency services appropriately, and to educate people about necessary precautions.

Storm warnings can be issued to enable the population to evacuate or prepare themselves for the storm, eg storing food and water or boarding up windows.

LEDCsLEDC: A Less Economically Developed Country [LEDC] has low levels of development, based on economic indicators, such as gross domestic product (the country's income). More of the countries in the southern hemisphere (eg countries in southern Africa, southern Asia and South America) are LEDCs, while more of the countries in the northern hemisphere are More Economically Developed Countries [MEDCs]. are often less prepared and may rely on aid (sometimes reluctantly) from MEDCs for the rescue and recovery process, eg Cyclone Sidr in Bangladesh, November 2007.

Case study: Hurricane Katrina 2005

The path of Hurricane Katrina

Impacts

• Katrina was a category 4 storm.
• Storm surges reached over 6 metres in height.
• New Orleans was one of the worst affected areas as it is below sea level, and protected by leveeslevee: Levees are ridges formed by deposits of alluvium left behind by the periodic flooding of rivers.. The defences were unable to cope with the strength of Katrina.
• Despite an evacuation order, many of the poorest people remained in the city.
• People sought refuge in the Superdome stadium. However conditions were unhygienic, and there was a shortage of food and water. Lootinglooting: Looting is a term which refers to stealing from unguarded homes or businesses. was commonplace throughout the city. Tension was high and many felt vulnerable and unsafe.
• 1 million people were made homeless and about 1200 people drowned in the floods.
• Oil facilities were damaged and as a result petrol prices rose in the UK and USA.

Responses

Flooding caused by Hurricane Katrina in New Orleans 2005

There was much criticism of the authorities for their handling of the disaster.

Although many people were evacuated, it was a slow process and the poorest and most vulnerable were left behind.

$50 billion in aid was given by the government.

The UK government sent food aid during the early stages of the recovery process.

The National Guard was mobilised to restore and maintain law and order in what became a hostile and unsafe living environment.

Drought

Droughts occur when a long period of abnormally dry weather leads to a severe water shortage. Extreme weather conditions are not the only cause of droughts, however – they are often caused by the activity of man as well. Human activities that can help trigger droughts include:

• Constructing a dam on a large river may help provide electricity and water to irrigate farmland near the reservoir. But it may also cause drought downstream by severely reducing the flow of water.
• Widespread cutting down of trees for fuel reduces the soil’s ability to hold water, - drying out the ground, triggering desertificationdesertification: Desertification is the spread of desert conditions in arid regions due to human activities, drought or climate change., and leading to drought.

Effects of drought

Parched ground during drought in Namibia

• Droughts endanger people's lives and livelihoods through thirst, hunger (due to crops dying from lack of water) and the spread of disease.
• Millions of people died in the 20th century due to severe drought and famines. One of the worst hit areas was the Sahel region of Africa, which covers parts of Eritrea, Ethiopia and the Sudan.
• Droughts and famines can have other geographical impacts - for example, forcing people to migrate to a new home, thus putting pressure on resources in neighbouring countries.
• Droughts can have severe impact in MEDCs as well as LEDCs. Droughts in Europe in recent years have caused deaths especially amongst the elderly. In the UK in summer 2006, there were hose pipe bans and campaigns to make people save water.

Drought in the Sahel

Map showing location of Sahel

Food for distribution Yabelo area, Southwest Ethiopia

The Sahel region of Africa has been suffering from drought on a regular basis since the early 1980s. The area naturally experiences alternating wet and dry seasons, but if the rains fail, it can cause drought and much suffering.

In addition to natural factors, the land is marginal, and human activities such as overgrazing, over-cultivation and collection of firewood can lead to desertificationdesertification: Desertification is the spread of desert conditions in arid regions due to human activities, drought or climate change., particularly when combined with drought conditions.

The result is crop failure, soil erosion, famine, and hunger, which then means that people are less able to work when their need is greatest. In Niger in 2004, a plague of locusts consumed any remaining crops which made the situation worse It becomes a vicious circle and can result in many deaths, especially among vulnerable groups such as infants and the elderly. People then rely on food aid from the international community.

Food aid in itself is unsustainable in the long term. What is really needed is development aid, which involves the local community in education in farming practices.

Case study: the impact of drought in the UK, 2004

The years 2004 – 2006 were one of the driest periods on record in the UK.

The South East of England is particularly vulnerable to drought due to the high population density – 13 million people live in the region – and the demand for water resources. There are few reservoirs, therefore there is a heavy reliance on groundwater supplies. Two consecutive dry winters meant that these supplies were not replenished.

Drought warning in Devon

• Hose-pipe bans were introduced in an effort to conserve water.
• Ground-water fell to its lowest level on record.
• Some rivers dried up.
• Low river flow means that pollution has a greater impact on the environment.
• Fish are more likely to die because of low flow, low oxygen levels, and higher water temperatures.
• Kew Gardens introduced a range of measures to conserve water, eg only watering newly planted trees, and newly turfed areas.

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