Tropical Storms

• Typhoon Haiyan was a 5 on the Saffir Simpson scale, with wind speeds over 200km/hr
• Typhoon Haiyan affected the island archipelago of the Phillippines, in East Asia in the Western Pacific Ocean.
• The Phillippines is made up of 7000 island and is in an area where 33% of all tropical storms occur annually, so there should have been a heightened hazard perception
• Impacts of Typhoon Haiyan

  • 6300 official deaths, but most likely 10,000
  • 2 million homeless
  • 90% of Tacloban destroyed in 7m storm surge
  • $2.9 billion in damage
  • Over 300mm of rain
• Responses to Typhoon Haiyan

  • UK sent over 200,000 tonnes of aid
  • Only 100 of the 1300 allocated police went out
  • $788 million aid from the UN
  • Tent schools and cash for work schemes
  • 25,000 of 205,000 promised houses built
• Hurricane Maria was a category 4 storm, with wind speeds over 175mph
• Huricane Maria mainly affected Puerto Rico in the Carribean Sea
• Puerto Rico has long suffered slow violence, it is classed as a HIC as it is a territory of the US, 40% of the population live below the poverty line and it is in $73 billion debt to the US
• Hurricane Maria was the 10th most intense Atlantic storm on record, and 2017 was the most expensive Carribean storm season
• Impacts of Hurricane Maria

  • Estimated 3000 death
  • No electric for 2 weeks
  • 60% of people got denied help by FEMA due to a lack of resident papers
  • $90 billion damage
  • Floods of 6 foot
  • 70,000 evacuated
• Responses to Hurricane Maria

  • Aid had been used in the prior Hurricane Irma, very little to go around
  • The Trump administration prevented $20 billion from reaching Puerto Rico
  • Population fell by 14%
  • Caused a mental health crisis still present over a year later
• A tropical storm is also known as a cyclone (India), hurricane (North Atlantic) and typhoon (south-east Asia)
• Tropical storms can extend to 500km in diameter
• By definition, tropical storms must have average wind speeds in excess of 75mph
• The most powerful and damaging part of a tropical storm is the menacing bank of cloud that rings the central eye, this is called the eye wall. Surrounding this is cloud and rain in a series of waves moving out
• The highly localised nature of tropical storms makes them difficult to predict and their impact can be highly destructive
• Most tropical storms form between 5 degrees North and South of the equator
• Factors needed for a tropical storm

  • Above the ocean
  • High temperatures
  • Atmospheric instability
  • Rotation of the Earth
  • Uniform wind direction
• Oceans = Tropical storms derive their moisture through evaporation and energy (in latent heat) from the oceans
• High temperatures = Tropical storms need a sea surface temperature in excess of 26 C, this is why they form in low latitudes during summer
• Atmospheric Instability = Tropical storms are most likely to form in areas of atmospheric instability, where warm air is rising. The inter tropical convergence zone is where the two limbs of the Hadley cell converge to form low pressure.
• Rotation of the Earth = Tropical storms require the Coriolis effect where there is a certain amount of spin which starts the topical storm spinning
• Uniform wind direction = Winds from different directions prevent tropical storms from gaining height and intensity, the vertical development is 'sheared off' with multiple winds
• Once a tropical storm has started to form, it will soon develop its distinct and clearly defined rotation. Warm, moist air rises rapidly in its centre, to be replaced by air drawn in at the surface. A central vortex will develop as more and more air is drawn in and rises. The very centre of the storm (the eye) is often characterised by a column of dry, sinking air.
• As the air rises, it rapidly cools. This leads to condensation and the formation of towering cumulonimbus clouds. Sometimes a number of isolated thunderstorms will coalesce to form a single giant storm. When condensation occurs, latent heat is released, which effectively powers the storm.
• Tropical storms continue to grow until it reaches land the supply of energy and moisture is released
• Storm Surge = High surges of water, typically up to about 3m in height which are swept in land. They are a combination of the intense low atmospheric pressure of tropical storms and powerful surface winds.
• The warm, humid air associated with a tropical storm can generate torrential rainfall, often in excess of 200 mm in just a few hours. This can trigger flash flooding at the coast, particularly in urban areas where surface water can overwhelm the drainage system.
• It has been estimated that up to 90 per cent of landslides each year are caused by heavy rainfall, and many are triggered by tropical storms.
• The intense rainfall increases pore water pressure (hydrostatic pressure within a slope), which weakens cohesion and triggering slope failure.
• There is some evidence that load release caused by tropical storminduced landslides may trigger earthquakes in tectonically stressed regions. E.g. 2010 Taiwan earthquake occured just 2 years after Typhoon Haiyan with 300mm of rain in five days.
• Tropical storms are classified according to the Saffir-Simpson scale, which is based on wind speeds. It doesn't take into account rainfall or the area directly impacted by the storm.
• There is no clear evidence that the number and intensity of tropical storms are increasing as global temperatures increase, in the past two decades there have been several years with high numbers, but the pattern is erratic
• There is logic to assume that a warmer atmosphere will hold more moisture, but this is countered by increased wind sheer acting as a negative feedback loop.
• Tropical storms can be predicted to some extent, they are mostly restricted to the tropics and pek from late summer into autumn
• Every year, the NOAA (US National Oceanographic and Atmospheric Administration) publishes the predictions of hurricane activity based on sea-surface temperatures, atmospheric and the climatic cycles such as El Nino and La Nina
• A hurricane return period is the frequency at which a certain intensity of hurricane can be expected within a given distance of a given location.
• Tropical storms can be prepared for through education, public awareness campaigns, preparing emergency supplies and planning evacuation routes
• Satellites and other technology can identify and track tropical storms, computer models which are based on historical data enable scientists to predict the likely course or track of an individual storm
• Mitigating tropical storms involves

  • Structural Response = hard engineering such as sea walls to protect against storm surge, and property reinforcements to protect against wind
  • Disaster Aid = Once the government declare emergency, this triggers disaster aid which can help provide food and water and for locating missing people
  • Insurance = People take insurance out against wind damage, so that when the storms hit they can get money to rebuild