Classification of Climate : Koeppen and Thornthwaite

  Koeppen’s Classification


  Thornthwaite Classification


Based on water budget/water balance. If the rainfall in a place is less than ET its water deficient. He used formula for water surplus and water deficit

Area having water surplus are humid climate and that having deficit are arid climates

Thornthwaite introduced his theory in1931 and was modified in 1948. The system was based on Precipitation efficiency and Thermal efficiency

Classifying climates concentrates on a local scale

This system is especially useful for soil scientists, water resources specialists, and agriculturalists

Modified Thornthwaite system  (1948) is based on the concept of potential evapotranspiration (potential ET), which approximates the water use of plants with an unlimited water supply

Precipitation-efficiency index

An index based on the ratio of mean monthly rainfall and temperature values in relation to evaporation rates.

Summation of monthly values gives an annual precipitation-efficiency index (P/E), which is used to define major climatic regions

P/E = 115 (P/T – 10)10/9

PE Index = ∑ PE over year

Temperature/Thermal Efficiency

The second criteria was based on Temperature efficiency

Temperature efficiency was given by

T/E    =   T – 32/4

Temperature Efficiency Index was summation of T/E for an year

Got 120 climatic zones out of which only 32 applies in real world

Modified Thornthwaite system (1948)

Actual climate zones can be classified based on PET

Ia = Aridity Index; Ih = humidity index; Im = moisture index)

Index in modified method

  • Aridity Index (Ia)
  • Humidity Index (Ih)
  • Soil Moisture Index (Im)

PET >Precipitation  = Soil Moisture 0/-ve

Precipitation > PET  = Soil Moisture +ve

Moist Climate determined by Aridity Index (variability in summer and winter)

Dry climate by Moisture Index

Thermal Efficiency Index

Moisture Index

Aridity Index

Soil Moisture Index

 

 

Koeppen Vs Thornthwaite Classification

Koeppen classification was simple, no calculation, dependent on only temp and precipitation but not supported by many as no base/cause of classification and no formulas were discussed

 

Thornthwaite system involved lot of calculation but was accepted by many geologist as cause and proofs were given. Was not good for tropical climates

  Classification of Climate


Have you ever wondered why the climate varies so much in different part of the world and why some of the parts though very distant but still have similar climate. The climate classification is based on meteorological parameters that varies from place to place over a long period of time.

Lets discuss few important type of classifications of climate. In this section of the tutorial we will be talking about two main classification koeppen and Thornthwaite classification

  Indian Climate Classification : Koeppen


Koeppen’s Classification of Climatic Regions of India is an empirical classification based on

  • Mean Monthly Temperature
  • Mean Monthly Precipitation
  • Mean Annual Rainfall

Koeppen identified a close relationship between the distribution of vegetation and climate

He selected certain values of temperature and precipitation and related them to the distribution of vegetation and used these values for classifying the climates

Koeppen recognized five major climatic groups, four of them are based on temperature and one on precipitation.

The capital letters:

A, C, D and E delineate humid climates and B dry climates

The climatic groups are subdivided into types, designated by small letters, based on seasonality of precipitation and temperature characteristics.

The seasons of dryness are indicated by the small letters : f, m, w and s, where

  • f – no dry season,
  • m – monsoon climate,
  • w – winter dry season and
  • s – summer dry season

The mentioned major climatic types are further subdivided depending upon the seasonal distribtion of rainfall or degree of dryness or cold

  • a: hot summer, average temperature of the warmest month over 22°C
  • c: cool summer, average temperature of the warmest month under 22°C
  • f: no dry season
  • w: dry season in winter
  • s: dry season in summer
  • g: Ganges type of annual march of temperature; hottest month comes before the solstice and the summer rainy season
  • H (heiss): average annual temperature under 18°C
  • m (monsoon): short dry season

The capital letters S and W are employed to designate the two subdivisions of dry climate:

  • semi-arid or Steppe (S) and
  • arid or desert (W)

Capital letters T and F are similarly used to designate the two subdivisions of polar climate

  • tundra (T) and
  • icecap (F)

  Thornthwaite Classification


Based on water budget/water balance. If the rainfall in a place is less than ET its water deficient. He used formula for water surplus and water deficit

Area having water surplus are humid climate and that having deficit are arid climates

Thornthwaite introduced his theory in1931 and was modified in 1948. The system was based on Precipitation efficiency and Thermal efficiency

Classifying climates concentrates on a local scale

This system is especially useful for soil scientists, water resources specialists, and agriculturalists

Modified Thornthwaite system  (1948) is based on the concept of potential evapotranspiration (potential ET), which approximates the water use of plants with an unlimited water supply

Precipitation-efficiency index

An index based on the ratio of mean monthly rainfall and temperature values in relation to evaporation rates.

Summation of monthly values gives an annual precipitation-efficiency index (P/E), which is used to define major climatic regions

P/E = 115 (P/T – 10)10/9

PE Index = ∑ PE over year

Temperature/Thermal Efficiency

The second criteria was based on Temperature efficiency

Temperature efficiency was given by

T/E    =   T – 32/4

Temperature Efficiency Index was summation of T/E for an year

Got 120 climatic zones out of which only 32 applies in real world

Modified Thornthwaite system (1948)

Actual climate zones can be classified based on PET

Ia = Aridity Index; Ih = humidity index; Im = moisture index)

Index in modified method

  • Aridity Index (Ia)
  • Humidity Index (Ih)
  • Soil Moisture Index (Im)

PET >Precipitation  = Soil Moisture 0/-ve

Precipitation > PET  = Soil Moisture +ve

Moist Climate determined by Aridity Index (variability in summer and winter)

Dry climate by Moisture Index

Thermal Efficiency Index

Moisture Index

Aridity Index

Soil Moisture Index

 

 

Koeppen Vs Thornthwaite Classification

Koeppen classification was simple, no calculation, dependent on only temp and precipitation but not supported by many as no base/cause of classification and no formulas were discussed

 

Thornthwaite system involved lot of calculation but was accepted by many geologist as cause and proofs were given. Was not good for tropical climates

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