Download Tropical Cyclones

Tropical Cyclones
Case Studies:
Cyclone Heta, Niue, 2004
Cyclone Zoe, Solomon Islands, 2002
Cyclone Kina, Fiji, 1993
Processes that produce tropical cyclones
The development of a cyclone is called cyclogenesis and occurs in the following
way:
1. The ocean is heated to 27◦C by the overhead sun (between November and
April). This causes warm moist air to rise and to condense into clouds.
2. As surface air rises a low pressure cell forms along the South Pacific
Convergence Zone (SPCZ), drawing in the surrounding warm air.
3. The rising air spins clockwise due to the Coriolis Effect that deflects winds.
Huge storm clouds form.
4. A jet stream or jet streams suck air from the top of the cyclone causing air
to rush into the system even faster, speeding the cyclone’s development.
Cyclone Heta – jet stream present that had a vacuum effect.
Sequence of events in a tropical cyclone
Before the tropical cyclone:
- Pressure falls and wind speeds increase dramatically. Cyclone Zoe –
pressure fell to 900hPa
- Cyclone warning and preparations: windows are boarded by, roofs are
secured, schools and businesses close, ripe fruit is picked, animals
and boats are brought in. Cyclone Heta – cyclone alert issued the day
before. Workers went home to secure houses. Boats were lifted out of
the water and the airport was closed.
During the tropical cyclone:
- Torrential rain, hurricane force winds and storm surge cause severe
damage to any thing in the cyclones path. Cyclone Heta – 200mm rain,
winds exceeding 250km/h, 4-7m high storm surge. Cyclone Zoe – 1m
storm surge, 350km/h winds
- People take shelter. They usually shelter in the strongest buildings and
in the highlands (mountains). Cyclone Zoe – people fled to mountain
shelters
- Deaths and injuries: mainly due to drowning, being hit by flying debris
or crushed by collapsed buildings. Cyclone Heta – one person killed.
Cyclone Kina – 22 people died either drowning or hit by flying debris.
- Widespread destruction: business buildings, homes, schools and
community buildings are destroyed. Cyclone Heta – Hotel Niue
destroyed, phone system and homes destroyed. Cyclone Kina – homes
had roofs blown off, no water, electricity or communications, three
major bridges destroyed.
After the tropical cyclone:
- Emergency response: search and rescue, evacuations, etc. Cyclone
Heta – evacuation centres were set up for those who had to leave their
homes. Cyclone Zoe – survivors had to wait more than a week for help
to arrive by sea.
- Clean-up and Assessment: the clean up begins, overseas aid comes in,
temporary shelters are set up and essential services are restored.
Cyclone Heta – New Zealand gave $5 million. New Zealand and
Australian aid workers went to Niue to help. Cyclone Kina – New
Zealand sent 200 tents and emergency supplies.
- Repair and Reconstruction: there is a decrease in tourism, new crops
are planted (only subsistence at this stage), income is lost and
rebuilding starts. Cyclone Heta – slowly reestablished the coconut and
fruit tree plantations, loss of income from expected 2700 tourists.
Cyclone Kina – some damaged hotels on the Coral Coast were forced
to close.
- Recovery: repairs to infrastructure, planning for reducing the effects of
tropical cyclones in the future and life goes on – tropical cyclones are a
part of Pacific life. Cyclone Heta – capital, Alofi, relocated to the centre
of the island. Cyclone Kina – 3 major bridges took 6 months to rebuild.
Effects of a tropical cyclone on the land
-
-
-
-
Coastal erosion: storm surges alter the shape of the island and can
destroy or change the shape of coral reefs. Cyclone Heta – shape of
the sea cliffs and the coral reef changed.
Flooding: low lying areas are flooded by storm surge, rainfall or rivers.
Cyclone Heta – flooding occurred in coastal areas. Washed away top
soil. Cyclone Kina – there was widespread flooding due to the heavy
rainfall.
Landslides: occur on steep and unstable slopes as a result of heavy
rainfall. Cyclone Kina – landslides occurred in inland areas.
Wind damage: the wind causes damage and destruction to the natural
vegetation. Cyclone Heta – most trees were toppled, 80% of foliage
stripped, burnt by salt spray.
Salinisation: salt from the storm surge contaminates the soil and
affects its fertility. Cyclone Heta – soil was contaminated by salt and
become inhospitable to plants.
Social effects of a tropical cyclone
-
-
-
Deaths and injuries: caused by drowning, falling debris and collapsed
buildings. Cyclone Heta – 1 dead. Cyclone Kina – 22 dead from flying
debris and drowning.
Damage and destruction: to homes, schools, churches and other
community buildings. Cyclone Heta – 100s of homes destroyed (10% of
population homeless) and the hospital also destroyed. Cyclone Kina –
2000 people evacuated from homes which were covered in mud or had
roofs blown off.
Disease: stagnant water and “off” food. Cyclone Kina – outbreak of
diarrhoea from people eating food that had gone off.
-
No drinking water: supplies cut or contaminated. Cyclone Heta – no
running water, supplies contaminated with salt. Cyclone Kina – piped
water supplies cut, salt contamination caused people to use muddy
water from rivers.
Economic effects of a tropical cyclone
-
-
-
-
Reduced income: from agriculture because of crop losses and from
tourism because of the damage to hotels. Cyclone Heta – Hotel Niue
was destroyed, loss of income from expected 2700 tourists, $240000
of crops lost. Cyclone Kina – 30% of sugar cane was destroyed, rice
crop and dairy industry were wiped out, hotels on the Coral Coast
damaged.
Cost of rebuilding: both business building and infrastructure. Cyclone
Heta - $20 million to clean up, $25 million to rebuild, phone system
destroyed. Cyclone Kina - $140 million damage, 3 major bridges
destroyed, 3000 telephone lines wiped out.
Dependence on foreign aid: they have to depend on other countries to
help them rebuild and help their people. Cyclone Heta – New Zealand
gave $5 million.
Better rebuilding: towns and cities are rebuilt in safer locations and
using better methods. Cyclone Heta – capital, Alofi, relocated to centre
of island.
How people increase the effects of tropical cyclones
-
-
-
Living and working around the coast: this means people are
concentrated in the areas that are most affected by tropical cyclones.
Cyclone Heta – most development was around the coast including the
capital, Alofi.
Growing cash crops: crops such as sugar cane and rice that are grown
for profit are not as cyclone resistant as traditional crops such as taro.
The tropical cyclone can wipe out the entire cash crop making the
country reliant on foreign aid. Cyclone Kina – 30% of sugar cane
destroyed and rice crop wiped out.
Lack of reliable communication: remote islands and villages do not
receive warnings so people aren’t prepared.
How people decrease the effects of tropical cyclones
-
Evacuate: move people to higher ground. Cyclone Zoe – people took
shelter in the mountains.
Monitoring of cyclones: means that people can be warned and
evacuated. Cyclone Heta – people were warned the day before.
Preparedness: people should know what to do and have emergency
kits ready for if a tropical cyclone strikes.
Building stop banks: to stop major flooding.
Building codes and land-use zoning: to stop people from building in
hazardous areas and to make sure that buildings are strong.
Cyclone resistant crops: grow these type crops (e.g. potatoes) that are
not easily damaged by winds.