- Climate types are generally classified based on temperature, precipitation, and seasonal patterns.
- Earth’s climates can be grouped into three major patterns - tropical, temperate, and polar.
1. Tropical Climate Types
- Found between the Tropics of Cancer and Capricorn (23.5° N/S).
- Receive the most direct sunlight, leading to consistently high temperatures (average annual temperature > 20°C).
- Experience high precipitation, often exceeding 1500–3000 mm annually.
- Little variation in daylight hours throughout the year.
- Controlled by the Hadley cell and the Intertropical Convergence Zone (ITCZ), a band of low pressure bringing heavy rainfall and thunderstorms.
Equatorial Tropical Climate
- High temperature and humidity year-round.
- Monthly rainfall typically above 60 mm, no true dry season.
- Supports tropical rainforest biomes, the most productive and biodiverse ecosystems on Earth.
Example
The Amazon Rainforest (Brazil) receives 2,500 mm of rainfall annually and is home to ~10% of global species diversity.
Seasonal Tropical Climate
- Found in regions with alternating wet and dry seasons (e.g., East Africa, India, Northern Australia).
- Total rainfall remains high (>1000 mm/year) but concentrated in a few months.
- Long dry season leads to fire-adapted vegetation.
Example
Tropical Savanna:
- Found in regions like the African Serengeti and parts of Australia.
- Characterized by grasslands with scattered trees, and large herbivores like zebras and elephants.
Note
- Seasonal variation in rainfall, not temperature, drives the vegetation cycle.
- Plant growth peaks during the wet season, and dormancy during the dry.
2. Temperate Climate Types
- Found between the tropics and polar regions.
- Experience distinct seasons (spring, summer, autumn, winter).
- Average temperatures:
- Warmest month >10°C
- Coldest month >−3°C
- Annual precipitation varies between 500-2,000 mm.
- Strongly influenced by latitude, ocean proximity, and prevailing winds.
Maritime Climate
- Found on the western coasts of continents where westerly winds bring moist air inland.
- Mild, wet winters and cool, dry summers due to oceanic heat storage.
- Supports temperate forests, often dominated by deciduous trees (oak, beech, maple).
Example
Western Europe’s mild winters are sustained by the North Atlantic Drift, a warm ocean current.
Continental Climate
- Found in the interior of continents, far from oceanic influence.
- Hot summers and cold winters due to the lack of moderating effects of water.
- Greater annual temperature range.
- Rainfall often occurs in the summer months.
Example
- Temperate Grassland:
- Found in the Great Plains of North America and the Steppes of Russia.
- Prairies dominated by grasses, with few trees due to seasonal droughts.
- Boreal Forest (Taiga):
- Found in Canada, Scandinavia, and Russia.
- Dominated by coniferous trees (e.g., pines, spruces) adapted to cold, snowy winters.
3. Polar Climate Types
- Located near the poles - the Arctic and Antarctic regions.
- Extremely cold year-round: average monthly temperature below 10°C.
- Low precipitation (<250 mm/year), mostly as snow.
- Long, dark winters and short summers; often windy.
- Tundra: Sparse grasses, lichens, mosses.
- Ice Cap: Permanent ice, no vegetation.
- Animals: Polar bears (Arctic), penguins (Antarctic), musk ox, arctic fox.
Example
Siberia, northern Canada, northern Scandinavia.
Natural Biome Development vs. Human Interference
- While temperature and precipitation are the primary factors in determining biome distribution, secondary influences and human interventions can prevent a biome from developing as predicted.
- In the absence of urbanization or agriculture, natural vegetation and ecosystems would establish themselves according to the climatic conditions of the region.
Secondary Influences on Biome Development
Even in areas with ideal temperature and precipitation for a particular biome, other natural factors can alter biome formation:
1. Topography
- Elevation affects temperature (drops ~6.5°C per 1000 m) and precipitation (mountain rain shadows).
- Slopes facing the sun (southern in the Northern Hemisphere) are warmer and drier than shaded slopes.
- Mountain regions may have altitudinal zonation resembling latitudinal biome gradients.
Example
The Andes Mountains show tropical forest at the base, temperate forest mid-slope, and alpine tundra at high altitudes.
2. Soil Quality and Composition
- Soils vary in nutrient content, texture, and drainage, affecting vegetation growth.
- Nutrient-poor or sandy soils may support grassland instead of forest, even under adequate rainfall.
Note
- Fertile loam soils favor forests.
- Acidic or nutrient-deficient soils favor heathland or scrub.
3. Natural Disturbances
- Fire, hurricanes, floods, or volcanic eruptions can alter vegetation succession.
- Regular fires maintain savanna ecosystems by preventing tree overgrowth.
Example
African savannas persist due to periodic fires and grazing, despite having sufficient rainfall to support forests.
Human Interventions Preventing Natural Biome Formation
1. Deforestation
- Large-scale forest clearing for agriculture, mining, or urbanization alters albedo, evapotranspiration, and carbon storage.
- Forests replaced by croplands (e.g., oil-palm plantations in Borneo) drastically change the local climate and biodiversity.
2. Urbanization
- Conversion of natural land to cities alters temperature (urban heat islands) and drainage patterns.
- Reduces biodiversity and interrupts ecological connectivity.
Case study
Urban Biome Shift (London)
Naturally, southern England would support deciduous temperate forest, but urbanization has replaced it with artificial urban ecosystems characterized by modified microclimates, non-native flora and fauna, and increased heat retention.
3. Agriculture
- Converts diverse natural ecosystems into monocultures.
- Alters nutrient cycles and soil composition.
- Irrigated deserts (e.g., California’s Central Valley) sustain artificial temperate biomes in arid zones.
4. Pollution and Climate Change
- Air and soil pollution damage vegetation.
- Global warming alters precipitation patterns, further shifting biomes beyond natural boundaries.
Example
Urban heat islands mimic subtropical climates, supporting plant species otherwise native to warmer zones.
Tip
When asked why a predicted biome does not exist in a given climate zone, always mention both natural modifiers (topography, soil) and human drivers (deforestation, agriculture).
Self review
- Discuss how topography and soil quality can prevent the expected biome from developing.
- Explain how urbanization changes local climate and prevents natural biome formation.
- Describe how deforestation in tropical regions alters both local and global climatic conditions.
