Variable Weather and Changing Climate overview for N(A)-Level Geography (SEAB 2246): the elements of weather and how they are measured, what controls temperature and rainfall, the equatorial and monsoon climates, and how tropical thunderstorms form

What this topic demands

Variable Weather and Changing Climate asks you to measure the atmosphere, explain why places differ, and recognise the tropical climates and weather that shape Singapore and the region. In the N(A)-Level Geography syllabus (SEAB 2246), much of the credit comes from naming the right instrument and unit, linking each control to a clear cause, and reading data accurately from a climate graph. Always keep the distinction between weather (short-term, day to day) and climate (the long-term average) at the front of your mind.

This guide ties together the matching dot-point pages, each with its own practice. See the full set at /sg-n-level/geography/syllabus and the subject hub at /sg-n-level/geography.

The elements of weather and how we measure them

The elements of weather and their measurement are temperature (thermometer, in degrees Celsius), rainfall (rain gauge, in millimetres), humidity (hygrometer), wind speed (anemometer) and direction (wind vane), air pressure (barometer) and sunshine (sunshine recorder). Many instruments sit in a Stevenson screen, a white louvred box that shades them from direct sun and lets air pass, so readings are fair and comparable. For each instrument, be ready to state the unit and one point about correct use, such as placing a rain gauge in the open, away from buildings and trees, with its rim above the ground.

What controls temperature and rainfall

The factors affecting temperature and rainfall are best learned as cause-and-effect chains:

• Latitude: near the Equator the Sun is more overhead, so its rays are concentrated on a small area and heat it strongly; toward the poles the rays spread over a larger area and heat less.
• Altitude: temperature falls with height because the air is thinner and holds less heat, so highlands are cooler than lowlands at the same latitude.
• Distance from the sea: the sea warms and cools slowly, so coasts have milder, more even temperatures, while inland areas are hotter in summer and colder in winter.
• Relief and rainfall type: mountains force air to rise, cool and drop relief rainfall on the windward side, leaving a drier rain shadow behind. The other rainfall types are convectional (rising hot air) and frontal (warm air rising over cold air).

The equatorial and monsoon climates

The two tropical climates you must know are the equatorial and monsoon climates. The equatorial climate (like Singapore's) is hot all year, around 26 to 28 degrees Celsius with a very small temperature range, and has heavy rainfall every month, mostly from afternoon convectional storms. The monsoon climate is also hot but has a larger temperature range and a clear wet season and dry season, because the prevailing winds reverse with the seasons, bringing wet onshore winds at one time of year and dry offshore winds at another. The simplest exam test: equatorial is wet all year, monsoon has distinct wet and dry seasons.

Tropical thunderstorms

Convectional thunderstorms are the classic tropical weather event. On a hot, sunny day the ground heats up and warms the air above it; this warm, moist air rises, cools as it goes, and its water vapour condenses into towering cumulonimbus clouds. When the droplets grow heavy they fall as intense rain, often with thunder, lightning and strong gusts. These storms peak in the late afternoon and can cause flash floods, a real hazard in Singapore and the region.

Worked example: reading a tropical climate graph

Check your knowledge

Attempt these under timed conditions, then check the matching dot-point pages.

1. Explain the difference between weather and climate. (2 marks)
2. Name the instrument and unit used to measure rainfall, and give one point about its correct use. (3 marks)
3. Explain how latitude affects the temperature of a place. (3 marks)
4. Describe two features of the equatorial climate. (2 marks)
5. Explain one way the monsoon climate differs from the equatorial climate. (2 marks)
6. Explain how a convectional thunderstorm forms on a hot afternoon. (4 marks)