Notes on Weather and climate
Updated 22 Feb 2014 for the new syllabus
Factors influencing the temperature of locations
10. Describe and explain the weather and
climate of Singapore with reference to rainfall, relative humidity and
temperature.
Hygrometer / psychrometer to measure relative humidity
Read and record the temperature on the dry bulb thermometer.
Refer to the relative humidity chart.
Read the temperature of the dry bulb thermometer on the left column. The depression of the wet bulb is the difference between the wet bulb thermometer and the dry bulb temperature.
Find the value at which the dry bulb temperature intersects with the depression of the wet bulb.
Wind vane and wind sock to measure wind direction
Wind direction refers to the direction that the wind is blowing from.
It is shown by a freely moving pointer on a wind vane. The wind vane is usually placed on a high, open place with little or no obstruction to the flow of wind. The direction the wind vane is pointing to is the direction where the wind is blowing from.
A windsock is a kite made from a tube of cloth. One end of the tube is held open by a ring. Windsocks point in the direction opposite of the wind's direction of origin. For example, if a windsock is pointing west, the wind is coming from the east. The faster the wind blows the straighter and more horizontally the wind extends. A 15-knot (28 km/h; 17 mph) wind will fully extend the properly functioning windsock. A 3-knot (5.6 km/h; 3.5 mph) breeze will cause the windsock to orient itself according to the wind.
Anemometer / pocket weather tracker to measure wind speed
An anemometer is used to measure wind speed and direction. It includes 3 to 4 cups mounted on a vertical pole. The cups catch the blowing wind and turn the pole. Each time the anemometer makes a full rotation, the wind speed is measured by the number of revolutions per minute (RPM). The number of revolutions is recorded over time and an average is determined.
Wind rose to record wind
Barometer to measure air pressure
A barometer has two hands. The hand on the inside is called the measuring hand. The hand on the outside directly over the measuring hand is called the movable pointer. The moveable pointer is arranged over the measuring hand to mark the current pressure. The measuring hand will move according to the air pressure. Take the reading to see whether the hand moves to right which is rising or to the left which is falling.
The dial expresses mercury in measurements in millibars (Mb).
12. Discuss
climate change in the last 150 years.
Limitations
Contributed to an estimated 60,000 trees planted yearly throughout Singapore by the National Parks Board. Limitations: Trees take many years to mature, so the positive effects of tree planting will take time to materialise. E.g. Angsanas, Raintrees and Yellow Flames take25 years to reach their full height.
19.Describe the location and characteristics of tropical cyclones
• Occurrence of tropical cyclones
– 8–15° latitude from the Equator
– Warm sea temperature greater than 26.5°C
21. What are the
impacts of tropical cyclones?
Physical
1. Differentiate
between weather and climate.
Weather
is the condition of the atmosphere at a particular place and time whereas
climate is the average condition of the atmosphere of a specific place over a
long period of time, usually over 30 years.
2. Calculate the following:
Mean daily temperature – sum of hourly
temperatures divided by 24 hours
Diurnal temperature range –maximum
temperature minus minimum temperature
Mean monthly temperature – sum of mean
daily temperatures in the month divided by number of days in the month
Mean annual temperature – sum of mean
monthly temperatures in the year divided by 1
Annual temperature range – maximum
temperature minus minimum temperature recorded in a year
Daily rainfall - the amount
of rain that falls over 24 hours
Monthly rainfall - total amount of
rainwater collected throughout the month
Annual rainfall - total amount of
rainwater collected throughout the year.
3.
Explain the daily and seasonal variations in temperature at a particular
location.
· Temperature
varies throughout the day in a place.
The temperature rises and falls as the Earth rotates from west to east.
The location facing the sun experience day and the location which is away from
the sun experience night. Temperature rises during the day and falls at night.
· Temperature generally increases with
the length of the day. Places along the equator have equal lengths of day and
night all the year. Beyond the equator, places have longer days and hence higher
temperatures in summer, and shorter days and lower temperatures in winter.
Temperatures are higher from June to August in the Northern Hemisphere due to
the position of the sun in relation to the Earth’s axis which is tilted at an
angle of 23½° from the vertical. From June to August because of the position of
the overhead sun, there is a higher intensity of the sun rays in the northern
hemisphere. Thus the temperatures are higher during this period.
4. Compare and explain
the variations in temperature between different locations.
Factors influencing the temperature of locations
Ø
Latitude
– Temperature generally decreases with increasing latitude. Places in low
latitudes have higher temperatures because they receive vertical sunrays and
hence more concentrated insolation. Temperatures are higher as the vertical
sunrays travel through shorter distance of the atmosphere and smaller amount of
insolation is lost through reflection and scattering.
Ø
Altitude
- The atmosphere is mainly heated by long wave radiation (heat energy) from the
earth's surface (land or sea surfaces). Thus, the higher the altitude, the
cooler the air temperature. With increasing altitude or elevation, air becomes
less dense and contains less dust and water vapour. . Heat from the earth's
surface thus escapes more rapidly, thereby lowering the air temperature. In
general, air temperature decreases with increasing altitude at a rate of about
0.6°C to 0.65°C per 100 metres (or 6°C to 6.5°C per 1000 m) in a free
atmosphere. This change of temperature gradient is called the normal lapse rate
(or vertical lapse rate).
Ø
Distance
from the sea- Land heats up and cools faster than water or the sea.
Maritime effect - onshore winds
blowing from the sea or ocean to coastal regions tend to lower summer
temperatures and raise winter temperatures. Such moderating influence is called
maritime influence and is confined to coastal areas. Thus, coastal regions have
a cooler summer and a warmer /milder winter than inland regions. The annual
range of temperature in coastal regions is therefore smaller than that in
inland regions. This is particularly felt in temperate regions.
Continental effect - Inland regions
situated at a great distance from the sea have hotter summers and colder
winters than coastal regions. The annual range of temperature in inland regions
is greater, and the climate is thus more extreme than that of coastal areas
Ø
Cloud
cover - Blanket effect of cloud produces small diurnal and annual ranges of
temperature. Clouds reduce the amount of solar radiation that reaches the
earth's surface and re-radiation that leaves the earth's surface. The dense
cloud cover in equatorial / tropical regions reduces intense solar heating of
the land in the daytime. At night thick clouds prevent rapid loss of long wave
radiation (heat energy) from the earth's surface. . The result is that daytime
temperatures in tropical equatorial regions do not rise too high (rarely
exceeding 33°C) even though the angle of the mid-day sun is high. On the
other hand, night temperatures in these regions do not fall too much. The
diurnal range and annual range of temperature are therefore small. e.g.
Singapore and other equatorial regions. Absence of cloud cover leads to great
diurnal range of temperature. The cloud cover in deserts tends to allow maximum
solar heating of the land in the daytime. Thus daytime temperatures rise high
(often exceeding 38°C). At night there is little cloud cover in desert regions.
There is rapid and maximum loss of heat energy by radiation from the heated
land surface, and temperatures fall to 21°C or below 0°C. This produces a great
diurnal temperature range in desert regions.
e.g. Sahara Desert
5.
Explain the differences in relative humidity in different locations.
The
amount of water vapour in the air affects relative humidity. For example, if
the air at 15°C holds 5g/m³ of water vapour and can contain a maximum of 10
g/m³of water vapour, relative humidity will be 50%. If the actual amount of
water vapour held by the air increases to 6 g/m³, relative humidity will be 60%
instead.
Relative
humidity also varies with temperature. Warm air can hold more water vapour than
cool air. When temperature increases, the amount of water vapour in the air
stays the same, but the rise in temperature makes air more able to hold water
vapour. Thus relative humidity decreases as temperature increases.
6.
Explain the formation of convectional
rain and relief rain.
Convectional
rain- When the earth’s surface is heated by conduction, moisture-laden vapour
rises because heated air always expands and becomes lighter. Air rises in a
convection current after a prolonged period of intense heating. In ascending,
its water vapour condenses into cumulonimbus clouds with a great vertical
extent. This probably reaches its maximum in the afternoon when the
convectional system is well developed. Hot, rising air has a great capacity for
holding moisture, which is abundant in regions of high relative humidity. As
the air rises, it cools and when saturation point is reached, torrential
downpours occur, often accompanied by thunder and lightning.
Relief
(orographic) rain is formed whenever moist air is forced to ascend a mountain
barrier. It is best developed on the windward slopes of mountains where the
prevailing moisture laden winds come from the sea. The air is compelled to rise
and is thereby cooled by expansion in the higher altitudes and the subsequent
decrease in atmospheric pressure. Further ascent cools the air until the air is
completely saturated. Condensation takes place forming clouds and eventually
rain. On descending the leeward slope, a decrease in altitudes increases both
the pressure and the temperature; the air is compressed and warmed.
Consequently, the relative humidity will drop. There is high evaporation and
little or no precipitation.
7. Explain how coastal temperatures are
moderated by land and sea breezes.
In coastal regions, the land is heated
up faster than the sea during the day and the hot air rises resulting in lower
pressure over the land than the sea. The air pressure over the sea is higher
and thus the air moves towards the land as sea breeze. At night, the land cools
faster and thus the air pressure over the land is higher than the sea. The air
moves towards the sea as land breeze.
Sea breezes usually blow at about
mid-afternoon when the temperature difference between the land and the sea is
the greatest. This lowers the relatively warmer temperature of the land. Land
breezes, on the other hand, cool the warm air over the sea at night. Thus land
and sea breezes help to regulate the temperatures of the land and the sea,
keeping it at a moderately constant level.
8. Explain the formation of monsoon winds.
Monsoon
winds are regional wind patterns that reverse direction seasonally due to the
Coriolis effect produced by the rotation of the earth. The Coriolis effect
cause the wind to be deflected. In the northern hemisphere, the wind is
deflected to the right and to the left in the southern hemisphere.
Between
June and September, the northern hemisphere experience summer and the air over
Central Asia heats up, expands and rises, forming a region of low pressure over
the area. The southern hemisphere experience winter and the low temperature
causes the air to be cold and dense, resulting an area of high pressure over
Australia. Air from Australia moves towards Central Asia as the southeast
monsoon due to the difference in pressure between Central Asia and
Australia, As the wind cross the
Equator, the Coriolis effect deflects the wind to the right and it become the southwest
monsoon.
Between
October and February, the southern hemisphere experience summer and an area of
low pressure forms over Australia The
northern hemisphere experience winter and the low temperature causes the air to
be cold and dense, resulting an area of high pressure over Cental Asia. Air
from Central Asia moves towards Australia due to the difference in pressure between Central Asia and Australia. The Coriolis effects deflect the wind to the right in the northern hemisphere as the northeast monsoon. As the wind crosses the equator, the Coriolis
effect deflects the wind to the left and it become the northwest monsoon in the southern atmosphere.
9.
Describe and explain the distribution and
characteristics of equatorial, monsoon and cool temperate climates.
Equatorial climate
Distribution: Between
10°N and 10°N of the equator e.g. Singapore, Johor in Malaysia
Characteristics: High
mean temperature of about 27°C
throughout the year because of the high angle of incidence of the sun’s rays
concentrating at the Equator. The temperature range is small, about 2 to 3°C.
High relative humidity of over 80% experienced throughout the year. Due to the
high temperatures, water evaporates quickly into the air, forming clouds and
convectional rain. Total annual rainfall is high at more than 2000mm throughout
with no dry month.
Tropical Monsoon climate
Location: Between 5°N
and 25°N and S of the equator e.g. Mumbai, India
Characteristics:
High temperatures around 29°C in the hot season due to the midday sun
being overhead at the Tropic of Cancer in June. Mean temperatures are lower in
the cool season ranging from 20°C. to 24°C in Dec and Jan, the coolest months.
The annual range of temperature is larger than that of the equatorial, ranging
from 5°C to 17°C. The rainfall is mainly affected by the monsoon winds which
cause a distinct wet and dry season. The onshore monsoon brings the rainy
season while the offshore monsoon causes the dry season. In India Bay of Bengal and therefore it is relatively dry towards
the end and beginning of the year. The SW monsoon brings heavy rain to the
coastal areas as the wind is laden with moisture it had picked up when crossing
the Indian Ocean .
Cool Temperate
Location: Between 45°N
and 60°N and S of the equator e.g. Paris in France, Moscow in Russia
Characteristics:
Four distinct seasons of spring, summer, autumn and winter due to the tilt of the earth and its revolution around the sun.
Four distinct seasons of spring, summer, autumn and winter due to the tilt of the earth and its revolution around the sun.
During
winter, these places have shorter day and less energy from the sun, This
results in a large temperature range with winter temperature below 0°C.
Total
annual rainfall is lower between 300mm and 900mm. There are no distinct wet or
dry seasons.
Singapore experiences the hot, wet
equatorial climate. Mean annual temperature is high at about 27.5°C. Surrounded
by water and accompanied by the high temperatures, especially at mid-day, leads
to a high evaporation rate. The air is humid or saturated with water vapour by
late afternoon. The dry- bulb reading will fall with temperatures towards
night, closing the gap between the readings on the two thermometers. Since the
wet bulb depression becomes very low, relative humidity is very high at around
84.2%. Total annual rainfall is high at about 2, 200mm. Most of the rain in
Singapore comes from convectional rain. However the northeast monsoon does
bring more rain to Singapore from Oct to Feb amounting to about 1,125mm as it
crosses the South-china sea and picks up more moisture.
11. Explain
the use of the following weather instruments:
Maximum
and minimum thermometer to measure the maximum and minimum temperatures
When
temperature rises, the mercury expands, pushing the metal index along the tube.
When temperature falls, the alcohol contracts and pulls the metal index along
the tube.
For
the Six’s thermometer (U-shape maximum and minimum thermometer), the
temperatures are obtained by reading the values indicated at the bottom of the
metal index (indicators).
Rainfall Gauge to measure the rainfall
It consists of a funnel that
collects and channels rainwater into a container. The rainwater that is
collected is emptied after every 24 hours into a measuring cylinder. It should
be placed in an open area where there are no obstructions to block the rain and
also avoid concrete surfaces as splashing may occur leading to an inaccurate
reading.
Hygrometer / psychrometer to measure relative humidity
Read and record the temperature on the dry bulb thermometer.
Refer to the relative humidity chart.
Read the temperature of the dry bulb thermometer on the left column. The depression of the wet bulb is the difference between the wet bulb thermometer and the dry bulb temperature.
Find the value at which the dry bulb temperature intersects with the depression of the wet bulb.
Wind vane and wind sock to measure wind direction
Wind direction refers to the direction that the wind is blowing from.
It is shown by a freely moving pointer on a wind vane. The wind vane is usually placed on a high, open place with little or no obstruction to the flow of wind. The direction the wind vane is pointing to is the direction where the wind is blowing from.
A windsock is a kite made from a tube of cloth. One end of the tube is held open by a ring. Windsocks point in the direction opposite of the wind's direction of origin. For example, if a windsock is pointing west, the wind is coming from the east. The faster the wind blows the straighter and more horizontally the wind extends. A 15-knot (28 km/h; 17 mph) wind will fully extend the properly functioning windsock. A 3-knot (5.6 km/h; 3.5 mph) breeze will cause the windsock to orient itself according to the wind.
Anemometer / pocket weather tracker to measure wind speed
An anemometer is used to measure wind speed and direction. It includes 3 to 4 cups mounted on a vertical pole. The cups catch the blowing wind and turn the pole. Each time the anemometer makes a full rotation, the wind speed is measured by the number of revolutions per minute (RPM). The number of revolutions is recorded over time and an average is determined.
Wind rose to record wind
A wind rose records the number of
days with and without wind, as well as wind direction. The number in the centre
records the number of calm days in the month. The rectangles point in the
direction the wind is blowing from and the numbers represent the dates in a
month in which the wind blew from a particular direction.
Barometer to measure air pressure
A barometer has two hands. The hand on the inside is called the measuring hand. The hand on the outside directly over the measuring hand is called the movable pointer. The moveable pointer is arranged over the measuring hand to mark the current pressure. The measuring hand will move according to the air pressure. Take the reading to see whether the hand moves to right which is rising or to the left which is falling.
The dial expresses mercury in measurements in millibars (Mb).
Changes in climate
·
Global
records since 1881 show a significant, but irregular temperature rise of 0.3oC
to 0.6°C.
·
Global
cooling was recorded after WWII for several decades because of industrial
pollution and volcanic activity (global dimming).
·
Global
warming over the last century: world is warming on average by 0.74°C, with most
of that since 1970s.
·
Global
temperatures in the last decade reached the highest levels on record.
13. Discuss
the natural causes of recent climate change.
Solar variations - The Sun is the
source of energy for the Earth’s climate system. Some scientists suspect that a
portion of the warming in the first half of the 20th century was due to an
increase in the output of solar energy. As the sun is the fundamental source of
energy that is instrumental in our climate system it would be reasonable to
assume that changes in the sun's energy output would cause the climate to
change. For instance a decrease in solar activity was thought to have triggered
the Little Ice Age between approximately 1650 and 1850, when Greenland was
largely cut off by ice from 1410 to the 1720s and glaciers advanced in the
Alps.
Volcanic eruptions - When a volcano
erupts it throws out large volumes of sulphur dioxide (SO2), water vapour,
dust, and ash into the atmosphere. Large volumes of gases and ash can influence
climatic patterns for years by increasing planetary reflectivity causing
atmospheric cooling. Tiny particles called aerosols are produced by volcanoes.
Because they reflect solar energy back into space they have a cooling effect on
the world. The greenhouse gas, carbon dioxide is also produced.
Ocean current - Ocean currents
move vast amounts of heat across the planet. Winds push horizontally against
the sea surface and drive ocean current patterns. Interactions between the
ocean and atmosphere can also produce phenomena such as El Niño which occur
every 2 to 6 years. Deep ocean circulation of cold water from the poles towards
the equator and movement of warm water from the equator back towards the poles.
Without this movement the poles would be colder and the equator warmer. Changes
in ocean circulation may affect the climate through the movement of CO2 into or
out of the atmosphere.
Earth orbital changes - The earth makes
one full orbit around the sun each year. It is tilted at an angle of 23.5° to
the perpendicular plane of its orbital path. Changes in the tilt of the earth
can lead to small but climatically important changes in the strength of the
seasons, more tilt means warmer summers and colder winters; less tilt means
cooler summers and milder winters. Slow changes in the Earth’s orbit lead to
small but climatically important changes in the strength of the seasons over
tens of thousands of years. Climate feedbacks amplify these small changes,
thereby producing ice ages.
14. Explain
the greenhouse effect.
Greenhouse
gases (CO2, water vapour, nitrous oxide, methane, ozone and halocarbons) trap
heat in the atmosphere resulting in a greenhouse effect. Incoming shortwave radiation from the sun
passes through the greenhouse gases in the atmosphere. Most of the shortwave
radiation is absorbed by the earth’s surface which heats up as a result. The
warmed surface of the earth emits longwave radiation to the atmosphere.
Greenhouse gases absorb longwave radiation and warm the atmosphere.
Enhanced
greenhouse effect is a rise in global temperatures due to the increase in the
concentration of the greenhouse gases.
15. Explain
how human activities (Anthropogenic factors ) such as deforestation, burning of
fossil fuels, rice cultivation and cattle farming increase greenhouse gases and
lead to enhanced greenhouse effect.
- Deforestation alters atmospheric
composition e.g. carbon dioxide and nitrous oxide, and affecting
hydrological cycle
-
Forest
absorbs CO² via photosynthesis. Deforestation lead to increase in CO² level in
the atmosphere.
-
Carbon
oxidation is a process by which carbon in the soil reacts with oxygen in the
atmosphere to produce CO². Deforestation exposes soil to sunlight and increase
soil temperature and rate of carbon oxidation which release more CO² into the
atmosphere.
- Changing land use
-
Agriculture
·
Rice
cultivation – tractors running on fossil fuels release CO². Use of chemical
fertilisers increases the amount of nitrous oxide in soil which is then
released when soil is ploughed or when rain flows through the soil. Methane is
released when dead leaves and manure decompose rapidly in the rice field due to
high level of moisture in the soil
·
Cattle
ranching – cattle releases methane as a waste gas
-
Industries – burning of fossil fuel to produce
energy release CO² as well as manufacturing of goods release CO² as by-product.
-
Urbanisation – burning of fossil fuels to produce
energy for household activities in urban areas such as heating, cooling,
cooking and lighting. More cars, buses and other transportation also increase
greenhouse gas emissions. Constructing infrastructure and producing
construction materials also release greenhouse gases.
16. Explain
the impact of climate change such as sea level rise, extreme weather events and
human health.
§
Sea
level rise - threatens low lying areas and islands, increases risk of damage to
homes and buildings from storm surges that accompany tropical cyclones.
§
More
frequent extreme weather events e.g. heat waves, flood, drought and tropical
cyclones. Increased land and sea surface temperatures resulted in greater
amounts of water vapour and latent heat in a warmer atmosphere causing more
extreme weather events.
§
Spread
of some infectious insect-borne diseases e.g. heavy rainfall allows mosquitoes
to grow resulting in spread of malaria and dengue fever.
§
Higher
temperatures may lengthen the growing season in certain regions e.g. fruit
production in Eastern Canada, vineyards in Europe. Increase in the types of
crops such as blackberries and maize that can be grown in UK. However in China,
production of fruits such as apples and cherries or nuts such as almonds and
walnuts is reduced as these fruits and nuts require cool weather temperature.
Similarly in Canada, the production of wheat is reduced.
17. Describe International efforts to mitigate climate change.
Kyoto Protocol (UN Framework
Convention on Climate Change (UNFCCC)
·
Drawn
up in Kyoto, Japan on 11 Dec 1997 and came into force on 16 Feb 2005 to reduce
levels of greenhouses gases.
·
Countries
were obliged to reduce their combined greenhouse gas emissions by at least 5%
below their 1990 level from 2008 to 2012.
·
Greater
responsibility placed on 37 developed countries and the European countries as
they were mainly responsible for the high levels of greenhouse gas emissions as
a result of more than 150 years of industrial activity.
Depending on the
ability of each developed country, they help less developed countries reduce
their greenhouse gas emissions by providing them with funds.
Success:
·
Many
countries such as Austria, Finland, Greece, Ireland and Spain met or exceeded
target.
·
Countries
monitor and report their greenhouse gs emissions to ensure they are on track in
keeping to target.
·
Successful
in encouraging sustainable development.
·
The
Clean Development Mechanism (CDM) gave Certified Emission Reduction (CER) credits
to countries which carried our emission-reduction projects such as installing
energy-efficient infrastructure in less developed countries.
Limitations
·
Countries
such as Denmark, Sweden and UK did not achieve their targets.
·
The
Kyoto Protocol did not make it compulsory for countries with low greenhouse gas
emissions to provide energy-efficient technology to countries with high
greenhouse gas emissions.
·
Countries
which did not sign the Protocol continued to contribute significantly in the
global emissions.
Since 1997, global
emissions increased by 35%, mainly from China, India and USA
18. Describe National efforts to mitigate climate change.
Singapore Green Plan 2012
Singapore Green Plan 2012
·
Launch
in 2002 by the Ministry of the Environment to reduce greenhouse gas emissions
by using natural gas as an energy source
·
To
generate 60% of Singapore’s energy needs using natural gas by 2012 as it is a
cleaner form of energy compare to coal as it does not produce smoke.
Success:
- As early as 2010, about 79% of Singapore’s electricity generated from natural gas.
- Exceeded target ahead of schedule.
Limitations:
- Complex treatment plants needed to process natural gas
- High maintenance cost for pipelines as they are laid underground and need to be checked regularly for leakages.
Green Mark Scheme
·
Launched
by the Building Construction Authority (BCA)
·
Buildings
evaluated and certified according to how energy-efficient and environmental
friendly they are. Encourage more new ‘green’ buildings which are E.g.
buildings which run partly on solar energy.
Success:
·
Green
Buildings such as Plaza by the Park, Standard Chartered @ Changi and the
National Library reported energy savings of 15% to 35% compared to convention
buildings.
·
Reduce
greenhouse gas emission as less fossil fuels needed to generate electricity.
Limitations
- Construction companies and developers too conservative to adopt new ideas and material to build ‘green’ buildings
- Most costly as ‘green’ materials may be more expensive.
Plant-A-Tree Programme
·
Started
in 1971 as Tree Planting day by the Garden City Fund and Singapore Environment
Council
·
Residents
encouraged donating money to buy a tree or take part in tree planting events.
Success:Contributed to an estimated 60,000 trees planted yearly throughout Singapore by the National Parks Board. Limitations: Trees take many years to mature, so the positive effects of tree planting will take time to materialise. E.g. Angsanas, Raintrees and Yellow Flames take25 years to reach their full height.
19.Describe the location and characteristics of tropical cyclones
• Occurrence of tropical cyclones
– 8–15° latitude from the Equator
– Warm sea temperature greater than 26.5°C
· Characteristics of
tropical cyclones
–
Weather
systems developing over tropical or subtropical waters. Also known as typhoons
and hurricanes
–
Strong
winds exceeding 64 knots or 119 km/hr, circulate clockwise in the southern
hemisphere and counter clockwise in the northern hemisphere while spiralling
inward to the cyclone centre or eye due to the Coriolis effect.
In
the northern hemisphere, Coriolis effect deflects winds to the right, causing
tropical cyclones to move in anti- clockwise direction. In southern hemisphere,
winds are deflected to the left, causing tropical cyclones to move in clockwise
direction
–
Low
pressure with clear skies and calm winds at the eye
–
Tropical cyclones are also known as
hurricanes and typhoons
20. Discuss
the impact of tropical cyclones on human lives and the environment
·
Storm surges
–
A
storm surge is a sudden rise of sea level in which water is piled up against a
coastline beyond normal conditions at high tide
–
It is
also caused by a combination of low air pressure and strong winds
–
It is
formed when the intense low pressure in the eye causes sea level to rise and
strong winds push water towards the coast and create huge waves, giving rise to
a storm surge
–
Greatest destruction to coastal areas as massive flooding
can destroy property and cause high death tolls
–
Vessels are also being swept in from the coast and stranded
inland
–
For example in 2008, Hurricane Ike caused a storm surge of
between 4 to 6 metres above normal tide level in Texas and damaged property
estimated around US$ 24.9 billion
·
Strong Wind
–
Strong force of winds can damage or destroy infrastructure
as well as injure people
–
Winds also cause loose debris to fly and hit people and
buildings
–
For example, Hurricane Andrew attained strong wind speeds of
up to 177km/h and caused widespread damage to the Bahamas and various parts of
USA
·
Torrential rains
–
Tropical cyclones can result in inland flooding and also cause rivers and streams to overflow
–
For example, Hurricane Isabel in 2003 flooded rivers flowing
across Virginia and Washington and affected areas 120 times the size of
Singapore causing damages of more than US$2.23billion.
–
Heavy rainfall also destabilize slopes when too much water
is in the soil and this could result in a landslide
–
For example, Typhoon Megi created landslides in Taiwan,
destroying buildings and roads
Damage
to infrastructure such as bridges and roads, houses and buildings
Disruption
of communi-cation - Roads and bridges were not able to be used to transport
emergency supplies such as food, medicine, water to the areas that need these
items
For
example, in 2009, Typhoon Ketsuna caused serious damage to the road networks in
the Philippines, Cambodia and Laos, which hindered rescue work
80%
of the health centres in Manila were destroyed by the tropical cyclone and it
became difficult to distribute food and medicine to those who needed them
Economic
Cost
of repair to infrastructure - Fixing or renovating buildings
Loss
of income - Income lost due to inability to work during period of tropical cyclone
or damaged crops
US$4
billion needed to repair infrastructure and provide humanitarian aid (eg
medicine, water filter, tents etc) after Typhoon Nargis in Myanmar in 2008.
Economic
losses for countries affected by typhoons amount to US$26 billion annually,
projected to increase to US$55 billion by 2100.
Social
Disrupt
water supply - Burst sewage pipes will contaminate water.
Damage
to infrastructure disrupts supply of fresh water to people.
Spreading
of diseases -Stagnant water allows mosquitoes to breed, aiding the spread of
malaria and dengue.
Dirty
water also results in water-borne diseases such as cholera and typhoid fever.
Displacement
of people from homes - People lose their homes due to rising flood waters and
an example is the disaster caused by Hurricane Katrina which struck New
Orleans, USA in 2005
22. Describe the Emergency action (action taken when the
tropical cyclones occur)
i) Evacuation of people
Governments can move
people to cyclone proof places such as community cyclone shelter
These shelters are
usually located near homes and the use of these shelters has greatly reduced
the number of casualties in countries such as Bangladesh and India
ii) Provision of emergency aid
NGOs such as Red
Cross, Oxfam and Save the Children often organize and send relief teams to
countries struck by tropical cyclones
These organisations
provide victims with food, clothing, shelter and health care
An example is the aid
provided by the Red Cross when Typhoon Megi hit the Philippines in 2010
23. Evaluate the effectiveness of measures adopted to
mitigate the effects of tropical cyclones
i) Prediction and warning
ii) Land use Control – Coastal management and Floodplain
management
ii) Reducing vulnerability of Infrastructure
i) Prediction
and warning
Prediction:
One method of
predicting cyclones is by analysing long-term climate records
This method is effective because by analyzing
the pattern of occurrences, it helps to establish the pattern of occurrences
and the severity of past cyclones to predict future cyclones
However, this method has limitations because these
records of past events only indicate the frequency of tropical cyclones and
does not give accurate details about when future tropical cyclones will occur
Another prediction
method is by analyzing the path of current cyclone through computer modelling
This method is effective because it helps to
predict and establish the likely path the cyclone will take based on weather
information
These warning systems
for tropical cyclones allow people to be warned in advance and evacuate in time
Japan and America
have installed advanced prediction and warning systems, which allows people to
evacuate way before tropical cyclones arrive
However, this method has limitations because these
prediction paths may not be completely accurate as it is based on weather
information available at the particular point of time and the weather
conditions may change quickly
ii) Land
use control
Regulates the use of
land by placing restrictions on how the land can be used
This method may be effective as restrictions are
placed on areas along the coasts that are vulnerable to storm surges and
flooding and to discourage development in these vulnerable areas, and thus
reducing the number of casualties likely to be hit by these hazards
Developers are also
required to pay higher taxes for use of land along the coast, and this is to
discourage developments in these areas
Protected zones can
be allocated and these areas are not allowed to have any development, in
addition these protected zones serve as a barrier against storm surges and
flooding
However, this method has limitations because effective
implementation of such enforcement needs time and manpower
In addition, there
are many developments found along these coastal areas and many residents live
along these coastlines are often reluctant to move out
Government needs to
buy back the land to turn the land into recreational areas, which is also
costly
Floodplain
management
Floodplain
management: Master plan to reduce the flood damage potential
Mapping the land use
of an area and implementing measures to prevent floods
This method may be effective and can be achieved
by ensuring new developments on floodplains are not prone to flooding and
reducing flood damage potential in already developed floodplains
The master plan also
draws up evacuation plans ensuring people are able to leave a flooded area as
quickly as possible
However, this method has limitations because the measures
implemented might not be able to cope with the large amount of rainfall and
storm surge thus areas still get flooded
iii) Reducing
vulnerability of infrastructure
Infrastructure needs
to be able to withstand the impacts of tropical cyclones
Reducing the
vulnerability of infrastructure includes designing buildings that are resistant
to wind and water damage, regular inspection of river embankment and coastal
dikes for breaches due to erosion, and locating utility lines underground
Wind and water
resistant buildings by introducing galvanized steel hurricane ties that are
nailed to the roof to prevent it from being blown off by the strong winds of
tropical cyclones
A layer of secondary
water resistance is added to the roofs of houses to prevent leaking if the roof
is blown off during the tropical cyclone
For example, in
Florida, USA, the state government aids homeowners by employing specialized
companies to improve the design of the roof and the openings of houses
This measure is effective because the houses
of most citizens living on Jensen Beach in Florida suffered only minor roof
damage when Hurricane Wilma truck in 2005
Another effective measure is to construct
protective barriers such as river embankments and coastal dikes by the sides of
rivers to prevent a river from overflowing
For example, the
construction of a protective barrier along the coast in Apia, Samoa, protected
the coastline and the harbor when Cyclone Val struck the island in 1991
Utility lines such as
power and telecommunication lines and water supply networks can be placed
underground to avoid damage by strong winds and storm surges and this measure is effective because this
can ensure that services are maintained during and after a tropical cyclone
240. Case study of a Tropical Cyclone
Example:
Tropical Cyclone Yasi (originated near Fiji islands on 27 January 2011) and is
one of most significant tropical cyclones in the Pacific Ocean
Cyclone
Yasi was a category 5 tropical cyclone on Saffir-Simpson Hurricane Scale,
meaning wind speeds of > 200km/h and Yasi hit 290km/h
Caused
serious damage to the country (cost of damages up to US$3.5 billion)
What were the weather conditions and the damages
inflicted by Tropical Cyclone Yasi?
Weather
conditions
· Temperatures recorded
were above 26°C (ideal for the formation of tropical cyclone)
· A sudden dip in
atmospheric pressure over land changing as the tropical cyclone passed over it
· Heavy rainfall of
about 200–300 mm in 24 hours (similar to what Singapore receives in its
rainiest month, December!)
Damages
· Widespread flooding
from storm surges and a significant storm surge of 5.5 m in Cardwell
· Power supply cut for
over a month affecting 170,000 homes and restoration took a long time because
the power supplies were unable to cope with restoring power to the large number
of affected homes
· Banana plantations
and cane fields were destroyed, wiped out about 75% of Australia’s crop
production
How effective were the measures adopted to
mitigate the impact of Tropical Cyclone Yasi?
Despite
being a category 5 storm, death toll was low due to high level of disaster risk
awareness and preparedness
Many
people had their homes built to resist the effects of cyclones
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