1931 Classification
In his classification Koeppen in his classification of climate he included one more factor i.e. 'evaporation in his classification. For this he devised two indexes-
1. Precipitation Effectiveness
In this he defined climates on the basis of precipitation available for vegetation for this he devised a formulae for finding out Precipitation Efficiency Ratio (P/E Ratio):-
r - Mean Monthly Rainfall(in inches)
t - Mean monthly temperature (°F)
On the basis of above formulae he devised world climate in to five types of Moisture Zones:-
| Humidity Zones | Vegetation | P/E Index |
|---|---|---|
| A(Wet) | Rainforest | 127 |
| B(Humid) | Forest | 64-127 |
| C (sub-Humid) | Grasslands | 32-63 |
| D (Semi Arid) | Steppe | 16-31 |
| E (Arid) | Desert | Less than 16 |
Further he divided boundary between above by using 4 different subtypes dependent precipitation distribution:-
r - Adequate Rainfall in all seasons
s - Summer dry region
w - Winter dry region
d - All year rainfall deficit
Based above two classification he devised total 20 types climatic zones:-
1. Ar, 2. As, 3. Aw, 4. Ad, 5. Br, 6. Bs, 7. Bw, 8. Bd, 9. Cr, 10. CS, 11. Cw, 12. Cd, 13. Dr, 14. Ds, 15. Dw, 16. Dd, 17. Er, 18. Es, 19. Re, 20. Ed[post_ads]
Temperature/Thermal Effectiveness
This is basically the heat provided by soil and vegetation to environment. This is also defined as positive departure from freezing point.
Thermal Efficiency Ratio(T/E Ratio) is calculated by the following formula:-
Where,
t - mean monthly temperature (°F)
Base on above formulae he classified world into six Temperature provinces:-
| Temperature Provinces | Climate | T/E Index |
|---|---|---|
| A' | Tropical | More than 127 |
| B' | Meso-thermal | 64-127 |
| C' | Mico-thermal | 32-63 |
| D' | Taiga | 16-31 |
| E' | Tundra | 1.15 |
| F' | Frost | 0 |
Based on previous 3 classifications P/E Index, T/E Index and Precipitation distribution across seasons there are 120 probable climatic zones are possible but he classified world climate into 32 types on the world map. 1. AA'r, 2. AB'r, 3. AC'r, 4.BA'r, 5. BA'w, 6. BB'r, 7. BB'w, 8. BB's, 9. BC'r, 10. BC's, 11. CA'r, 12. CA'w, 13. CA'd, 14. CB'r, 15. CB'w, 16. CB'w, 17. CB'd, 18. CC'r, 19. CC's, 20. CC'd, 21. DA'w, 22. DA'd, 23. DB'w, 24. DB's, 25. DB'd, 26, DC'd, 27. EA'd, 28. EB'd, 29. EC'd, 30. D'(Taiga Climate), 31. E'(Tundra Climate), 32. F'(Polar Climate).
1948 Classification
In this classification he kept all factors which were devised earlier and added an additional method based on Potential Evapotranspiration which is discussed below:-
Potential Evapotranspiration
Basically this is a function of both the mean monthly temperature and mean monthly rainfall summed up on annual basis.
This indicates Thermal Efficiency and water loss i.e. the amount of moisture and heat transfer from the soil and vegetation thus it is a function of energy received by sun.
It is calculated by using mean monthly temperature. The formula is as follows:-
Thornthwait further devised 4 indices to define boundary between different climates as follows:-
1. Moisture Index
It represents moisture deficit and surplus.
Im = (100S - 60D)/PE
Im = Annual Moisture Index
S = Monthly surplus moisture
D = Monthly deficit Moisture.
based on this he devised nine type of climates: -
| Humidity Provinces | Climate | Im |
|---|---|---|
| A | Perhumid | >100 |
| B4 | Humid | 80-100 |
| B3 | Humid | 60-80 |
| B2 | Humid | 40-60 |
| B1 | Humid | 20-40 |
| C2 | Sub-Humid (moist) | 0-20 |
| C1 | Sub Humid (dry) | -33.3-0 |
| CD | semiarid | -66.7 to -33.3 |
| E | Arid | -100 to -66.7 |
2. Thermal Efficiency Index
It represents basically potential Evapotranspiration and calculated as above.
Based on this climate is again divided into nine Thermal provinces.
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3. Aridity and Humidity Index
Aridity Index - In moist climate, Annual water deficit, taken as PE (Annual) becomes Aridity Index.
Humidity Index - In Dry climates, Annual water surplus taken annual PE becomes Humidity Index.
Based on this climate is divided in two main and 10 subtypes [post_ads_2]
I. Moist Climate(A,B,C2)
| Moist Provinces | Climatic Conditions | Aridity Index |
|---|---|---|
| r | Little or no water deficit | 0-10 |
| s | Moderate Summer deficit | 10-20 |
| w | Moderate Winter water deficit | 10-20 |
| s2 | Large Summer water deficit | Above 20 |
| w2 | Large winter water deficit | Above 20 |
II. Dry Climate(C'1, D, E)
| Dry Provinces | Climatic Conditions | Humidity Index |
|---|---|---|
| d | Little or no water surplus | 0-16.7 |
| s | Moderate summer water surplus | 16.7-33.3 |
| w | Moderate winter water surplus | 16.7-33.3 |
| s2 | Large Summer water surplus | Above 33.3 |
| w2 | Large winter winter water surplus | Above 33.3 |
4. Concentration of Temperature Effectiveness
It refers to percentage annual mean potential Evapotranspirtion in three summer months.
Based on this eight types of climates are devised further
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Evaluation and Merits of the Scheme
Similar to Koeppen's Scheme in three ways:-
- Based on calculation and empirical formulae.
- Both related vegetation nd climates similarly.
- Both used letter symbols to indicate climate types.
But it differs with Koeppen :-
- In terms of P/E, T/E and PE, which was not used in Koeppon's Classification of Climate.
Merits
- It is comprehensive and formulae based approach.
- Scientific in nature.
- Links vegetation with climatic zones.
Demerits
- Very complex formulae which is difficult to calculate and comprehend.
- Delimitation of boundaries between two climatic zones become difficult and vogue due to a lot of calculation.
- Too much use of letter symbols make it difficult ot remember.
- Data of evaporation and moisture are difficult to collect.
- Thornthwait yielded 32 climate types, three times more than the Koeppon's Classification of Climate.