Storm Hazards: Flashcards
Nature of tropical storms:
A tropical storm is a low pressure spinning storm with torrential rain and high wind speeds.
Underlying causes of tropical storms:
Temperature - Ocean temperatures must be 27 degrees celcius and 50m deep. Warm water provides the storm with energy.
Air pressure - Convergence of air in the lower atmosphere, forces warm air to rise.
Wind shear - Winds must be present for the swirling motion to form, but not too strong otherwise the system will be ripped apart early on.
Rotation - Form 5 degrees around the equator, due to the coriolis effect
A trigger: An area of low pressure near the sea surface triggers the storm.
What is the coriolis effect:
The Coriolis Effect is the effect of the Earth’s rotation on weather events. The storm spins because the Earth is spinning; but there is no Coriolis Effect at the equator, hence why these storms will only form a certain distance away from it.
Characteristics of a tropical storm:
- Hundreds of Km wide
- Usually last 7-14 days
- Spin anticlockwise in the northern hemisphere and clockwise in the southern hemisphere.
- Centre of the storm is the eye, which is an area of low pressure.
- The eye wall is where the highest winds and rainfall is
- Above the storm, there is an outflow of moisture laden air so cloud cover extends for a long distance either side of the eye.
39 mph classed as a tropical storm
eye wall wind speeds at 74 mph.
Forms of storm hazards:
High winds
Storm surges
river flooding
coastal flooding
Landslides
High winds:
- Average wind speeds in access of 120km/h can reach around 250km/h
- Cause significant damage to infrastructure such as ripping off roofs, breaking windows and damaging communications.
- Flying debris can kill people
- Major transport disruption.
Storm surges:
Typically 3-5m
- Cause 90% of deaths in tropical storms
- Formed by a combination of low atmospheric pressure with driving surface winds.
- Pollute freshwater supplies.
- Destroy infrastructure.
River flooding:
Rainfall of 200mm in just a few hours can result in sudden increase in river discharge. to increase the risk of flooding.
- River flooding also sends more floodwater to other places.
Coastal flooding:
Extensive rainfall can cause flashfloods at the coast. Exacerbated by urbanisation.
Landslides:
90% of landslides each year are caused by rainfall.
Increased rainfall increases hydrostatic pressure within a slope, which leads to slope failure.
- Soil becomes heavier
- Hurricane mitch 1998, landlsides killed 18,000 people.
Spatial distribution of storm hazards:
- Vast majority are formed over the tropics.
Magnitude:
Measured on the Saffir Simpson scale.
Which is based on wind speeds (1-5)
Category 1 = winds of 120-150 kmh
Category 5 = winds over 250kmh
Also estimates how much damage a storm of a given magnitude will do.
Frequency:
- Increasing frequency due to global warming.
- Form in NH from June-November
- Form in SH from November- April
Around 100 occur each year.
Some never develop to be a major hazard.
Regularity:
No clear spatial or temporal pattern. Largely irregular.
The route taken depends on the climactic conditions.
Predictability of storm events:
Tropical storms form away from land meaning satellite tracking of cloud
formations and movement can be tracked and the general route can be
predicted.
The closer the hurricane gets, the easier it is to predict. Storm surges can also be predicted based on the pressure and intensity of the storm.
From past storms and climatic trends, the probability of a storm hitting an area can also be predicted. Scientists have predicted how many years it will take for a tropical storm to hit certain areas.
