The Thornthwaite climate classification is a climate classification system created by American climatologist Charles Warren Thornthwaite in 1931 and modified in 1948.
[1][2][3][4] Thornthwaite initially divided climates based on five characteristic vegetations: Rainforest, forest, grassland, steppe and desert.
Similarly to precipitation effectiveness, Thornthwaite also developed a T/E index to represent thermal efficiency.
Featuring six climate provinces: Tropical, mesothermal, microthermal, taiga, tundra and frost.
[6] After being criticized for making climatic classification complex, Thornthwaite switched vegetation with the concept of potential evapotranspiration (PET), which represents both precipitation effectiveness and thermal efficiency.
Each of the four climatic types can be described by an English alphabet letter and are arranged exactly by the order shown previously.
[2] As an example, B3s2A’b’4 (Tracuateua) describes a wet (B3), megathermal (A’) climate with a large summer water deficit (s2) and which more than 48% but less than 52% of the potential evapotranspiration is felt in the summer (b’4).
The driving factor in this system is the water budget of a region.
The Seasonal Variation of Effective Moisture is described by two indexes: The Aridity Index (Ia), used in wet climates to identify and quantify the severity of drought conditions, and the Humidity Index (Ih), used in dry climates to identify and quantify the severity of wet conditions.
, where D is the annual water deficit, S is the annual water surplus, and PET is the annual potential evapotranspiration[2] Furthermore, these indices are represented by four letters, which indicate the seasonal distribution of precipitation: r (constantly rainy), d (constantly dry), s (summer deficit or surplus) and w (winter deficit or surplus) and two numbers to indicate the severity.
Wet climates (A, B, C2) can be classified as: Dry climates (C1, D, E) can be classified as: The deficiency of water in the soil is calculated as the difference between the potential evapotranspiration and the actual evapotranspiration.
[2] The thermal efficiency index (TE) is defined as the annual potential evapotranspiration (PET)[2] and has five different classifications: Megathermal, mesothermal, microthermal, tundra and perpetual ice.
, where PET1, PET2 and PET3 are the estimated values of PET for the three hottest consecutive months.