Notes on Weather and climate

Updated 22 Feb 2014 for the new syllabus
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 the offshore NE monsoon does not bring rain except areas close to the 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.

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.


10. Describe and explain the weather and climate of Singapore with reference to rainfall, relative humidity and temperature.


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).




12. Discuss climate change in the last 150 years.


   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
·      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

  
21. What are the impacts of tropical cyclones?
Physical
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

However, this method has limitations because it involves regular inspection and maintenance and this costly as it means repairing any damage on these barriers and many countries might not have the resources to do it

 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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5 Response to "Notes on Weather and climate"

  1. Vienne ., on August 16, 2016 at 2:40 AM said:

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