Weather and climate
Weather is the condition of the atmosphere at a place at a given time. Climate is the average weather over many years (usually 30). The main elements are temperature, rainfall, humidity, wind and pressure. The factors that control climate are latitude, altitude, distance from the sea, ocean currents, winds and relief.
Main climatic regions
| Region | Climate | Natural vegetation | Examples |
|---|---|---|---|
| Tropical (equatorial) | Hot and wet all year, 25–28 °C, 2 000 mm or more | Dense evergreen rainforest | Congo basin, Amazon |
| Tropical (savanna) | Hot, wet and dry seasons, 800–1 200 mm | Savanna grassland | Serengeti, Tanzania |
| Tropical (desert) | Hot and very dry, under 250 mm | Xerophytes, scrub | Sahara, Kalahari |
| Sub-tropical (Mediterranean) | Hot dry summer and mild wet winter | Evergreen shrubs and trees | Mediterranean, Cape Town |
| Temperate | Mild, rain all year, four seasons | Deciduous and coniferous forest | Europe, eastern USA |
| Polar | Very cold, little precipitation | Tundra, ice | Arctic, Antarctica |
Climate and natural vegetation
Vegetation reflects climate. Heat and water decide what grows: rainforests where it is hot and wet, savanna where there is a dry season, desert scrub where it is very dry, and tundra where it is too cold for trees. Plants have adaptations: desert plants store water (succulents), have small leaves or deep roots; savanna trees have flat crowns and thick bark to resist fire.
Choose the latitude. This simple model gives the approximate mean annual temperature at sea level.
Key terms
- Climate
- The average weather of a place over many years.
- Weather
- The state of the atmosphere at a given time.
- Savanna
- A tropical grassland with scattered trees.
- Tundra
- Treeless polar vegetation.
Summary
- Climate is the long-term average of weather.
- Latitude, altitude, distance from the sea, winds and currents control climate.
- The main regions are tropical, sub-tropical, temperate and polar.
- Natural vegetation follows climate.