ZIMSEC O Level · Geography · Form 1, Form 2, Form 3
Weather is the day-to-day condition of the atmosphere; climate is the average weather over about 30 years.
Weather elements and instruments
- Temperature: maximum and minimum thermometers in a Stevenson screen.
- Rainfall: rain gauge (mm). Humidity: wet and dry bulb thermometers (hygrometer).
- Pressure: barometer. Wind direction: wind vane; speed: anemometer. Sunshine: Campbell-Stokes recorder.
Calculations
Mean daily temperature = (max + min) ÷ 2. Range = max − min. Annual rainfall = sum of monthly totals.
Types of rainfall
- Convectional: the ground heats air, which rises, cools and condenses into cumulonimbus clouds and thunderstorms – common in Zimbabwe's summer.
- Relief (orographic): moist air forced over mountains, e.g. the Eastern Highlands get heavy rain on the windward side; the leeward side lies in a rain shadow.
- Frontal (cyclonic): warm air rises over cold air. Tropical cyclones from the Indian Ocean (such as Cyclone Idai in 2019) can bring floods.
Zimbabwe's climate
Tropical, modified by altitude. Hot wet season (November–March), cool dry season (May–August), hot dry season (September–October). The highveld is cooler than the lowveld (Zambezi and Limpopo valleys). The Inter-Tropical Convergence Zone (ITCZ) brings most of the summer rain.
Exam tip: In climate graph questions, describe the pattern AND quote figures from the graph with units.
Check yourself
- Name the instrument used to measure wind speed.
- The maximum is 30 °C and the minimum 14 °C. Find the mean and the range.
- Why do the Eastern Highlands receive high rainfall?
Show answers
- Anemometer.
- Mean 22 °C; range 16 °C.
- Moist south-easterly winds are forced to rise over the mountains, cool and condense (relief rainfall).
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