Hurricanes (SL IB Geography)

• “Hurricane” is one of the names given to tropical storms:
  • Other names used for tropical storms include cyclones and typhoons
  • Storm names vary depending on the location in which they form
• Hurricanes form over waters in tropical or subtropical regions:
  • Hurricanes usually form in the Atlantic Ocean, the middle or northeast of the Pacific Ocean, the Caribbean Sea and the Gulf of Mexico
  • Hurricanes form in these regions as the waters are warmer
• Hurricanes tend to occur over the months of June – November
• The Pacific Ocean has the largest number of hurricanes per year
• More hurricanes occur in the northern hemisphere than in the southern hemisphere

Distribution of tropical storms

Distribution of tropical storms

• Hurricanes are low-air-pressure systems formed over oceans
• Hurricanes need warmer waters to form (minimum 27 degrees Celcius)
• Warm and moist air above the ocean rises upwards, leaving behind a pocket of low pressure underneath
• Cooler air moves into this low-pressure area, heats up and rises
• This air cools and condenses as it rises and releases heat energy, forming clouds and storms
• The Coriolis Effect causes a spinning action. Storms in a low-pressure system will spin clockwise in the southern hemisphere and anti-clockwise in the northern hemisphere
• As this process intensifies with more heat energy, winds will increase and the spinning will worsen
• Wind with low wind shear helps storm clouds rise straight upwards
• The centre of a hurricane is the eye:
  • This is a large area of low-pressure air that is colder and drier
  • It results in a calm centre inside the storm
• When hurricanes reach land or move over colder waters, they will lose energy and slow down
• The Saffir-Simpson scale shows the intensity of hurricanes, by measuring wind speed

Formation of a hurricane

Formation of a hurricane

• Hurricane paths are hard to predict. This makes it more difficult to prepare for and manage hurricanes
• Hurricane winds can rip up trees, cause airborne debris and damage infrastructure, e.g. homes, power lines etc.
• Hurricanes can cause a rise in the water level, resulting in storm surges. This can cause dramatic coastal flooding as the wind moves the water inland
• Flooding can occur inland as a result of heavy rainfall after the hurricane
• Hurricanes can affect boats and offshore oil/gas stations out on the ocean

Case Study – Hurricane Katrina

• Hurricane Katrina was a category 5 hurricane that hit the Gulf Coast in 2005
• It formed over the Atlantic Ocean, building up to be one of the most deadly hurricanes in history
• It battered the areas of Florida, Mississippi and Louisiana, among others

The path of Hurricane Katrina as it hit the southwest coast of the US

The path of Hurricane Katrina as it hit the southwest coast of the US

Impacts of Hurricane Katrina

• Roughly 1833 people died with millions of people left homeless
• Damages cost roughly $300 billion 
• New Orleans was the worst hit area:
• Storm surges caused intense flooding
• Levees and floodwalls were not strong enough to deal with the Category 5 storm
• This failure of flooding protection resulted in the dramatic loss of life
• Coastal erosion destroyed beaches
• Land and forests were destroyed, impacting habitats and ecosystems
• Residents were left stranded, causing tensions. This resulted in increased crime e.g. looting
• People did not have any electricity for up to a week
• Tourism was severely affected
• The hurricane affected the agriculture and oil/gas industry, negatively affecting the economy

Responses to Hurricane Katrina

• Evacuation during Hurricane Katrina was poorly planned:
  • Many underprivileged people were left stranded
• The US government provided $50 billion, whilst other countries sent aid relief 
• The Superdome (stadium) became a space for people to find shelter and food:
  • There were issues with food availability and unsanitary conditions 
• Eventually, repairs were made to the levees and floodwalls, however, it took many months until the water was gone
• Many people living back in New Orleans cannot get home insurance or have to pay very high premiums as a result of hurricane risk