Weather and Climate
Senior 1 · Geography
Weather and Climate
Lesson 1 of 6
22 min
Two pieces of advice you might hear in Rwanda: "Take an umbrella, it will rain this afternoon" and "Plant your beans at the start of the long rains in March." Both are about rain, but they are different kinds of statement. The first is about the weather: what the air is doing now or in the next few hours. The second is about the climate: what the weather is usually like, year after year.
Definition
Weather: the condition of the atmosphere at a particular place and time: its temperature, rainfall, humidity, wind, cloud, sunshine and pressure. It can change from hour to hour. Example: "Kigali this afternoon: 26 °C, cloudy, thunderstorm at 15:00."
Definition
Climate: the average weather of a place measured over a long period, usually 30 years, including its usual pattern through the year and its extremes. Example: Kigali has a mild climate with an average temperature of about 22 °C and two rainy seasons.
| Weather | Climate | |
|---|---|---|
| Time period | Hours or days | 30 years or more |
| Area | A small place at one time | A place or large region |
| Changes | Quickly, often within a day | Slowly, over decades |
| Studied by | Meteorologists (forecasting) | Climatologists |
| Example | "Heavy rain in Musanze tonight" | "Musanze is cooler and wetter than Kigali" |
| Element | Instrument | Unit |
|---|---|---|
| Temperature | Thermometer; maximum and minimum (Six's) thermometer | degrees Celsius (°C) |
| Precipitation (rainfall) | Rain gauge | millimetres (mm) |
| Humidity | Wet- and dry-bulb thermometers (hygrometer) | per cent (%) |
| Air pressure | Barometer | hectopascals (hPa) or millibars (mb) |
| Wind direction | Wind vane | compass points or degrees |
| Wind speed | Anemometer | km/h, m/s or knots |
| Sunshine | Campbell–Stokes sunshine recorder | hours |
| Cloud cover | Observation by eye | oktas (eighths of the sky) |
Definition
Weather station: a place where the elements of weather are measured with standard instruments at fixed times every day, so that records from different places and years can be compared. Rwanda's national weather service is Meteo Rwanda.
A thermometer left in the sun measures how hot the thermometer gets, not the air. So thermometers are kept in a Stevenson screen: a white, louvred box that shades them but lets air flow freely around them.
Figure 1. A Stevenson screen holds thermometers in the shade, in freely moving air, at a standard height.
Definition
Stevenson screen: a white, louvred wooden box on legs that holds thermometers in the shade, in freely moving air, about 1.25 m above short grass, so that they measure the true air temperature.
Worked example: choosing a site for the school weather station
A school has four possible sites: (a) next to the kitchen wall; (b) on the concrete of the assembly ground; (c) under a big eucalyptus tree; (d) on the open grass of the sports field, 20 m from any building. Which is best?
Answer: site (d). A good station is in an open, level place over short grass, at least twice the height of any building or tree away from it, and fenced so that nobody tampers with the instruments.
Important
Case study: Meteo Rwanda
Meteo Rwanda, the Rwanda Meteorology Agency, runs a network of weather stations across the country, including automatic stations that send readings every few minutes. It uses them, with satellite images and computer models, to issue daily forecasts, warnings of heavy rain before the rainy seasons, and seasonal forecasts that farmers use to decide when to plant. Records kept over many years at stations such as Kigali Airport describe Rwanda's climate, which you will study in Lesson 6.
The Stevenson Screen, by Learning Factory (5 min). Watch for the reason each design feature is there: white paint, louvres, double roof and legs.
Sort these statements into weather or climate, and explain one of your choices: (1) "It was 30 °C in Bugesera yesterday." (2) "The east of Rwanda is drier than the west." (3) "July is usually the driest month in Kigali." (4) "A hailstorm damaged crops in Nyabihu last week."
Tip
"Climate is what you expect; weather is what you get." If a statement uses words like usually, average, every year, it is about climate.
Practice
Remember
Sources and credits
Written by Ganzaa: the lesson text, Stevenson screen diagram, tables, worked example and practice.
