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 at about 24 km/h (15 mph) - wind speeds can reach over 120 mk/h (75 mph).

Map showing route of Hurricane Mitch, 1998

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. Sometimes the most destructive elements of a storm are the subsequent high seas and flooding.

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). are better placed to reduce the effects of tropical storms because they have more financial, educational and technological resources to help deal with them. They better able to observe and predict storm behaviour and can invest in infrastructure to withstand storms - as well as spending more money on repairing the damage caused.

How hurricanes form

• When this warm and wet air rises, it condenses to form towering clouds, heavy rainfall. It also creates a low pressure zone near the surface of the water.
• Rising warm air causes the pressure to decrease at higher altitudes. Warm air is under a higher pressure than cold air, so moves towards the ‘space’ occupied by the colder, lower pressure, air. So the low pressure ‘sucks in’ air from the warm surroundings, which then also rises. A continuous upflow of warm and wet air continues to create clouds and rain.
• Air that surrounds the low pressure zone at the centre flows in a spiral at very high speeds - anti-clockwise in the northern hemisphere - at speeds of around 120 km/h (75 mph).
• Air is ejected at the top of the storm – which can be 15km high – and falls to the outside of the storm, out and over the top, away from the eye of the storm. As this happens, it reduces the mass of air over the ‘eye of the storm’ - causing the wind speed to increase further. Some ejected air also cools and dries, and sinks through the eye of the storm, adding to the low pressure at the centre.
• The faster the winds blow, the lower the air pressure in the centre, and so the cycle continues. The hurricane grows stronger and stronger.
• Seen from above, hurricanes are huge circular bodies of thick cloud around 450 km (300 miles) wide. The cloud brings heavy rain, thunder and lightning.
• In the centre is the eye of the hurricane, about 45 km across (30 miles) across. Often there will be no clouds 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 cold air is descending.
• In the northern hemisphere, the prevailing easterly tropical winds tend to steer hurricanes toward land - although their course is unpredictable. As hurricanes move inshore, their power gradually reduces because their energy comes from sucking up moist sea air.

Cross section diagram of a hurricane

Preparation and prediction

Preparation and prediction techniques to help cope with hurricanes can be very different in 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). and 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)..

MEDCs

Bangladeshi villager affected by cyclone Sidr

MEDCs have the resources and technology, such as satellites and specially equipped aircraft, to predict and monitor the occurrence of storms. They are also equipped 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. People can prepare by storing food and water or boarding up their windows.

LEDCs

LEDCs are often less prepared. They may rely on aid (sometimes reluctantly) from MEDCs for the rescue and recovery process, as was the case with 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 because it is below sea level and protected by leveeslevee: Ridges or banks formed by deposits of alluvium left behind by the periodic flooding of rivers. Can also be artificially constructed banks or walls.. These protect it from the Mississippi River and Lake Ponchartrain. The levee defences were unable to cope with the strength of Katrina, and water flooded into the city.
• Despite an evacuation order, many of the poorest people remained in the city.
• People sought refuge in the Superdome stadium. Conditions were unhygienic and there was a shortage of food and water. Lootinglooting: 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 1,200 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. Droughts are also often caused by the activity of humans as well. Human activities that can help trigger droughts include:

• Widespread cutting down of trees for fuel. This reduces the soil's ability to hold water and dries out the ground, triggering desertification [desertification: The spread of desert conditions in arid regions due to human activities, drought or climate change. ], leading eventually drought.
• Construction of a dam on a large river. This may help provide electricity and water to irrigate farmland near the reservoir: however, it may also cause drought downstream by severely reducing the flow of water.

Effects of drought

Parched ground during drought in Namibia

• Droughts endanger 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. If drought forces people to migrate to a new home it could put pressure on resources in neighbouring countries.
• Droughts can have a severe impact on MEDCs as well as LEDCs. Droughts have caused deaths in Europe in recent years, especially among the elderly. During the UK summer of 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. If the rains fail it can cause drought.

In addition to natural factors, the land is marginal. Human activities such as overgrazing, over-cultivation and the collection of firewood can lead to desertification, 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. It becomes a vicious circle and can result in many deaths, especially among infants and the elderly. In Niger in 2004, the situation was made worse when a plague of locusts consumed any remaining crops. In these cases, people rely on food aid from the international community.

On its own, food aid is unsustainable in the long term. What is really needed is development aid, which involves educating the local community in farming practices.

Case study: the impact of drought in the UK (2004)

The years 2004-06 were one of the driest periods on record in the UK.

Southeast England is particularly vulnerable to drought because it has a high population density. There are 13 million people living in the region and the demand for water resources is high. There are few reservoirs, which means 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.
• Groundwater fell to its lowest level on record.
• Some rivers dried up.
• Low river flow meant that pollution had a greater impact on the environment.
• Fish were 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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