8.4 Climate classification systems

Climate classification systems help us understand Earth's diverse weather patterns. Köppen and Thornthwaite's methods use temperature and precipitation to categorize climates, but differ in their focus on vegetation versus water balance.

These systems divide the world into major climate zones like tropical, dry, temperate, continental, and polar. Each zone has distinct characteristics, influenced by factors such as latitude, altitude, and proximity to water bodies. Understanding these zones helps predict regional weather patterns and ecosystems.

Climate Classification Systems

Köppen vs Thornthwaite classification systems

• Köppen climate classification system
  • Based on temperature and precipitation patterns
  • Focuses on vegetation types as indicators of climate (rainforests, deserts, steppes)
  • Uses letters to denote main climate types (A for tropical, B for dry, C for temperate)
  • Further subdivides climate types using second and third letters (Af for tropical rainforest, BWh for hot desert)
• Thornthwaite climate classification system
  • Based on potential evapotranspiration and precipitation
  • Considers the water balance and moisture availability
  • Uses letters to denote moisture regimes (A for perhumid, B for humid, C for moist subhumid)
  • Further subdivides climate types using thermal efficiency and seasonal concentration of precipitation
• Comparison
  • Both systems use temperature and precipitation as primary factors
  • Köppen system emphasizes vegetation, while Thornthwaite focuses on water balance
  • Köppen system is more widely used and easier to apply
  • Thornthwaite system provides more detailed information on moisture availability (drought susceptibility)

Main climate zones

• Köppen climate zones
  • A: Tropical climates
    • Af: Tropical rainforest (Amazon Basin)
    • Am: Tropical monsoon (India)
    • Aw: Tropical savanna (African Serengeti)
  • B: Dry climates
    • BWh: Hot desert (Sahara)
    • BWk: Cold desert (Gobi)
    • BSh: Hot semi-arid (Australian Outback)
    • BSk: Cold semi-arid (Patagonia)
  • C: Temperate climates
    • Cfa: Humid subtropical (Southeastern US)
    • Cfb: Oceanic (Western Europe)
    • Csa: Hot-summer Mediterranean (Greece)
    • Csb: Warm-summer Mediterranean (Northern California)
  • D: Continental climates
    • Dfa: Hot-summer humid continental (Northeastern China)
    • Dfb: Warm-summer humid continental (Southern Canada)
    • Dwa: Monsoon-influenced hot-summer humid continental (Eastern Russia)
    • Dwb: Monsoon-influenced warm-summer humid continental (Manchuria)
  • E: Polar and alpine climates
    • ET: Tundra (Northern Siberia)
    • EF: Ice cap (Antarctica)

Criteria for climate classification

• Köppen climate classification criteria
  • Temperature
    • A: Average temperature of the coldest month ≥ 18℃
    • B: Average annual precipitation < 10 × (2 × average annual temperature)
    • C: Average temperature of the coldest month between -3℃ and 18℃
    • D: Average temperature of the coldest month ≤ -3℃
    • E: Average temperature of the warmest month < 10℃
  • Precipitation
    • f: No dry season
    • m: Monsoon climate
    • s: Dry summer (Mediterranean)
    • w: Dry winter
• Thornthwaite climate classification criteria
  • Moisture regimes based on moisture index ($I_m$)
    • $I_m = 100 × (P - PE) / PE$, where $P$ is precipitation and $PE$ is potential evapotranspiration
    • A: Perhumid ($I_m ≥ 100$)
    • B: Humid ($20 ≤ I_m < 100$)
    • C: Moist subhumid ($0 ≤ I_m < 20$)
    • D: Dry subhumid ($-33.3 ≤ I_m < 0$)
    • E: Semi-arid ($-66.7 ≤ I_m < -33.3$)
  • Thermal efficiency based on potential evapotranspiration
  • Seasonal concentration of precipitation (summer vs winter)

Global distribution of climate zones

• Use climate data (temperature and precipitation) to determine the climate type for a given location
• Create climate maps based on the classification systems
  • Identify spatial patterns and distribution of climate zones
  • Analyze the influence of factors such as latitude (Equator vs poles), altitude (mountains), and proximity to water bodies (coastal vs inland)
• Compare the distribution of climate zones between the two classification systems
  • Identify similarities and differences in the spatial patterns
  • Discuss the implications of using different classification criteria (vegetation vs water balance)
• Relate the distribution of climate zones to global circulation patterns and other climatic factors
  1. Hadley cell circulation and its impact on tropical and subtropical climates (rising air near Equator, descending air in subtropics)
  2. Westerlies and their influence on temperate climates (prevailing winds in midlatitudes)
  3. Polar front and its role in shaping polar and subpolar climates (boundary between cold polar air and warmer midlatitude air)