Topic 1

• what is weather ?

  it refers to the state of the atmosphere at a particular place and time, describe using variables including:

  • air temperature
  • cloud cover
  • precipitation
  • wind speed
  • wind direction
• what is climate ?

  • it is the average state of the atmosphere at a particular place over a long period of time, typically 25 years or more
  • there are many climate types around the world, including:
  • tropical equatorial climate
  • tropical monsoon climate
  • cool temperate climate
• what are the characteristics of tropical equatorial climate ?

  • generally high temperatures all year round, about 27 degrees
  • small annual temperature range of about 2 - 3 degrees
  • high annual precipitation of more than 2000 mm
  • precipitation falls evenly throughout the year
  • location between 10 degrees north and 10 degrees south of the equators

  eg. singapore, singapore
• what are the characteristics of tropical monsoon climate ?

  • generally high temperatures all year round, about 25 degrees
  • small annual temperature range of about 3 - 4 degrees
  • high annual precipitation of about 1500 mm
  • distinct wet and dry seasons
  • location between 5 degrees north and 30 degrees north of the equator, and 5 degrees south and 30 degrees south of the equator

  eg. kochi, india
• what are the characteristics of cool temperate climate ?

  • 4 distinct seasons of spring, summer, autumn and winter
  • large annual temperature range of about 21 degrees
  • annual precipitation is between 300 - 900 mm
  • precipitation falls evenly throughout the year
  • location between 45 degrees north and 60 degrees north of the equator, and 45 degrees south and 60 degrees south

  eg. paris, france
• how can climate types be represented ?

  climograph, showing average monthly temperature and rainfall over a year
• what are climatic hazards ?

  • climates are changing due to natural and human- induced causes
  • predictable weather patterns in many places are now beginning to change and becoming unpredictable
  • extreme weather events, such as heat waves, droughts, floods and wildfires are expected to occur more often or with greater severity
  • this can impact natural and human systems significantly
• how does air temperature vary over time ?

  • in a day
  • in a year
• why does air temperatures vary over time in a day ?

  • due to the earth's rotation on its own axis
  • one complete rotation around the axis takes about 24 hours
• how does air temperatures vary over time in a day ?

  • as the earth rotates, the side of the earth that faces the sun experiences day and receives solar radiation, thus it experiences higher temperatures
  • as the earth continues rotating, this side will eventually face away from the sun and experience night time where it does not receive solar radiation, thus experiences lower temperatures
  • temperatures are different at different times of the day
• describe how the temperature is during midday


  • the sun is directly overhead
  • due to the earth's spherical shape, solar radiation is spread over a smaller area
  • solar radiation is more concentrated
  • temperature is highest in the day

  eg. midday temperatures in sg can reach between 31 to 33 degrees
• describe how the temperature is before and after midday

  • the sun is not directly overhead
  • due to the earth's spherical shape, solar radiation is spread over a larger area
  • solar radiation is less concentrated
  • temperature is lower than midday

  eg. temperatures before and after midday in sg can range from 25 to 31 degrees
• describe how the temperature is before sunrise

  • at night, the place does not receive solar radiation and loses heat in the form of longwave radiation
  • thus, the temperature is lowest just before sunrise as the place has lost heat for the longest period of time

  eg. temperatures before sunrise in sg can range from 23 to 25 degrees
• why does air temperature vary over time in a year ?

  • mainly due to the earth's revolution around the sun
  • earth's axis is tilted at an angle of 23.5 degrees
  • as the earth revolves around the sun, the hemisphere wil receive different amounts of solar radiation over a year
• how does air temperature vary in june ?

  • due to the earth's tilted axis and its revolution around the sun, the northern hemisphere leans more towards the sun, receiving more direct solar radiation and experiences higher temperatures
  • due to the earth's tilted axis and its revolution around the sun, the southern hemisphere leans away from the sun, receiving less direct solar radiation and experiences lower temperatures
• how does air temperature vary in december ?

  • due to the earth's tilted axis and its revolution around the sun, the northern hemisphere leans away from the sun, receiving less direct solar radiation and experiences lower temperatures
  • due to the earth's tilted axis and its revolution around the sun, the southern hemisphere more towards the sun, receiving more direct solar radiation and experiences higher temperatures
• how does air temperatures vary in march and september ?

  • due to the earth's tilted axis and its revolution around the sun, neither hemisphere leans towards the sun, hence both experience moderate temperatures
  • the northern hemisphere experience spring in march and autumn in september
  • the southern hemisphere experience autumn in march and spring in september
• how does air temperature vary across place ?

  • latitude
  • altitude
• why does air temperatures vary due to latitude ?

  • at the global scale, temperatures are lower at higher latitudes
  • due to the earth's spherical shape, the solar angle varies at different parts of the earth
  • the higher the latitude, the smaller the solar angle, therefore solar radiation is less direct, is spread over a larger area and is less concentrated, leading to lower temperatures

  eg. beijing, china (40 degrees north) has temperatures of about 12 degrees, while singapore (1 degree north) has temperatures of about 29 degrees
• why does air temperatures vary due to altitude ?

  • at a local scale, temperatures are lower at higher altitudes
  • at higher altitudes, air is less dense and air pressure is lower as gravity pulls most of the air molecules towards the ground surface
  • with fewer air molecules, air has a lower ability to absorb and radiate heat from longwave radiation, leading to lower temperatures

  eg. average temperatures at genting highlands (altitude of 1700 m above sea level) is about 21 degrees while average temperatures in the surrounding areas (at sea level) is about 32 degrees
• what factors affect air temperature at specific sites ?

  • types of surface
  • distance from the sea
• how does type of surface affect air temperature ?

  • dark surfaces like exposed soil and forests generally absorb more solar radiation and radiate more heat, hence having higher temperatures
  • light coloured surfaces like clouds and snow generally reflect more solar radiation and radiates less heat, hence having lower temperatures
  • urban areas tend to have higher temperatures than the surrounding rural areas
• why do urban areas have higher air temperatures ?

  • urban areas have larger areas of dark surfaces like roads, which absorb more solar radiation and radiate more heat than forests and water bodies
  • glass- covered skyscrapers reflect sunlight to the ground surface, increasing absorption of solar radiation and heat radiation by ground surfaces

  eg. temperatures of sg CBD at night are 2 degrees warmer than the area near macritchie reservoir which has very dense vegetation
• how can distance from the sea affect air temperatures ?

  it can cause differences in temperatures between coastal and inland areas
• how is the temperature of coastal areas affected by distance from the sea ?

  • due to the maritime effect, they experience cooler summers and warmer winters
  • annual temperature range is lower than inland areas
• how is the temperature of inland areas affected by distance from the sea ?

  • due to continental effect, they experience hot summers and cold winters
  • annual temperature range is higher than inland areas
• why is there is difference in temperature depending on the distance from the sea ?

  • the sea heats up and cools down more slowly than land
  • during winter, the sea is warmer than land, warming the air along coastal areas
  • during summer, the sea is cooler than land, cooling the air along the coastal areas
  • inland areas do not experience this and instead experience the continental effect

  eg. anchorage, a coastal city in alaska, usa has a lower annual temperature range of 23 degrees while fairbanks, an inland city in alaska, usa, has a higher annual temperature range of 40 degrees
• describe the water cycle process

  1. water vapour enters the atmosphere through evapotranspiration
  2. as the water vapour rises, it cools and condenses into tiny water droplets at dew point temperature, forming clouds
  3. when the water droplets in the clouds become big and heavy enough, they fall to the ground as precipitation like rain or snow
  4. water on the ground surface infiltrates the subsurface soil and rock
  5. water flows over the ground surface as surface runoff and enters a body of water
  6. below the earth's surface, water moves horizontally above the impermeable rock as groundwater
• how can water vapour enter the atmosphere ?

  • sun's heat cause water from water bodies to evaporate, forming water vapour
  • plants give out water through transpiration
• what factors affect the rate at which water flows on and below the earth's surface ?

  • type of soil
  • how built- up an area is
  • presence of natural vegetation
• how does the type of soil affect the rate of water flow on and below the earth's surface ?

  • when the soil has larger pores like sandy soil, rather than ones with smaller pores like clayey soil
  • the larger pores allow more water to infiltrate, allowing the water to move much more quickly
• how does how built- up an area is affect the rate of water flow on and below the earth's surface ?

  • infiltration rates are lower in built- up areas where ground surfaces are covered in concrete which have tiny pores
  • the speed of surface runoff is higher on smoother ground surfaces such as roads and pavements in built- up areas, due to fewer obstructions and lesser friction
• how does the presence of natural vegetation affect the rate of water flow on and below the earth's surface ?

  • infiltration rates and groundwater flow are faster where there is vegetation as the roots of plants loosen the soil, creating more open spaces in the soil for water to pass through
  • the speed of surfaces runoff is lower on vegetable areas as the stems and roots of plants act as barriers and increase the surface roughness
• what is relative humidity ?

  it refers to the ratio of amount of water vapour in the air to the maximum amount of water vapour the air can hold at a given temperature
• how does temperature affect relative humidity of a place at a specific time ?

  when temperature increases, the amount of water vapour that air can hold increases, relative humidity hence increases
• what happens when air holds the maximum amount of water vaopur ?

  • the air is saturated
  • when relative humidity exceeds 100%, condensation occurs and this may occur when
  • more water vapour is being added to the air through evaporation
  • air temperature drops
• how are clouds formed ?

  • as air rises up in the atmosphere, it cools, reducing the amount of water vapour it can hold
  • the amount of water vapour in the air exceeds the maximum amount of water vapour the air can hold
  • at dew point temperature, air condenses into water droplets on condensation nuclei
  • condensation nuclei provides surfaces where water droplets can change into water droplets or solid ice crystals and form clouds
• how is rain formed ?

  • water droplets in the clouds collide and coalesce and become bigger and heavier
  • the water droplets fall to the earth as raindrops once they are large and heavy enough
• how is conventional rain formed ?

  1. in the day, heat from the sun is absorbed by the land, and the air above it gains heat
  2. the warm air rises and cools, and condenses on condensation nuclei at dew point temperature, forming clouds
  3. water droplets in the clouds collide and coalesce, and when they become large and heavy enough, they fall to the ground as rain

  eg. requent afternoon thunderstorms in sg
• how is relief rain formed ?

  1. prevailing winds pick up moisture over the sea, and push the moist air up the windward side of a mountain
  2. the rising moist air cools and condenses on condensation nuclei at dew point temperature, forming clouds
  3. water droplets in the cloud collide and coalesce, and when they become large and heavy enough, they fall to the ground as rain on the windward side
  4. as most of the moisture has fallen on the windward side, the leedward side experience dry descending air and is thus dry