THE KOPPEN CLIMATE CLASSIFICATION SYSTEM

THE KOPPEN CLIMATE CLASSIFICATION SYSTEM

 Introduction

The concepts of devising climate classes that combine temperature and precipitation characteristics, but of setting limits and boundaries fitted into known vegetation and soil distributions were actually carried out in 1918 by Dr. Wladimir Koppen of the University of Graz, in Austria. Koppen was both a climatologist and a plant geographer, so his main interest lay in finding climate boundaries that coincided approximately with boundaries between major vegetation types. Although he was not entirely successful in achieving his goal, his climate system has appealed to geographers because it is strictly empirical and allows no room subjective decisions.

The classification was subsequently revised and extended by his students to become the most widely used of climatic classifications for geographical purposes.

BASIS FOR THE CLASSIFICATION

The Koppen system is strictly empirical. This is to say that each climate is defined according to fixed values of temperature and precipitation, computed according to the averages of the year or of individual months. In such a classification, no concern whatsoever is given to the causes of the climate in terms of pressure and wind belts, air masses, fronts, or storms. It is possible to assign a given place to a particular climate sub-group solely on the basis of the records of the temperature and precipitation of that place, provided, of course, that the period of record is long enough to yield meaningful averages. Air temperature and precipitation are the most easily obtainable surface weather data, requiring only simple equipment and a very elementary observer education. A climate system based on these data has a great advantage, in that the area covered by each sub-type of climate can be delineated (outlined, profiled) for large regions of the world.

LIMITATIONS

As with any regional classification, this system is not universally applicable. It utilizes, for example, only the data or mean monthly temperature and precipitation. There is not provision for variations in the strength or constancy of winds, temperature extremes, precipitation intensity and range, amount of cloud cover, or the net radiation balance. Its greatest inadequacies perhaps lie in its application to humid dry boundaries, and it should not be considered for land management and planning purposes, where more precise and varied factors should be utilized.

ADVANTAGES

Despite these and other disadvantages, this system has been used mainly because of four reasons that have special value.
1. It has precise definitions that can be applied easily to standardize data that are available for locations throughout the world.
2. There is a reasonable correlation globally with major vegetation regions.
3. It requires a minimum amount of calculation.
4. It is widely used in educational circles throughout the world.

DESIGNATION OF VARIOUS TYPES

The Koppen features a short hand code of letters designating major climate groups, sub-groups within the major groups and further sub-divisions to distinguish particular seasonal characteristics of temperature and precipitation.

Major Groups Five major climate groups are designated by capital letters as follows: A–Tropical Rainy Climate: Average temperature of every month is above 64.4oF (18oC). These climates have no winter season. Annual rainfall is large and exceeds annual evaporation. B–Dry Climate: Potential evaporation exceeds precipitation on the average throughout the year. No water surplus; hence no permanent streams originate in B Climate Zones. C–Mild, Humid (Mesothermal) Climates: Coldest month has an average temperature under 64.4oF (18oC), but above 26.6oF (-3oC); at least one month has an average temperature above 50oF (10oC). The sea climates have both a summer and a winter season. D– Snowy Forests (Microthermal) Climates: Coldest month has an average temperature under 26.6oF. Average temperature of warmest month is above 50oF. E–Polar Climates: The average temperature of warmest month is blow 50oF. The climates have no true summer.   Four of these five groups (A, C, D and E) are defined by the temperature averages, whereas one (B) is defined by the precipitation to evaporation ratios. This procedure may seem to be of fundamental inconsistency. Groups A, C and D have sufficient heat and precipitation for both of high trunk trees, e.g., forest and woodland vegetation.

Sub-Groups

Sub-groups within the five major groups are designate by a second letter, according to the following codes:-

S – Steppe Climate: A semi-arid climate with about 15-30 inches (38-76 cm) of rainfall annually at low latitudes.

W – Desert Climate: Arid climate. Most regions included have less than 10 inches (25 cm) of rainfall annually.

The letters S and W are applied only to the dry B climates, yielding two combinations – BS and BW.

f:- Moist. Adequate precipitation in all months. No dry season. This modifier is applied to A, C and D groups, yielding combinations – Af, Cf and Df.

w:- Dry season in the winter of the respective hemisphere (low sun season). This modifier is applied to A, C and D groups, yielding combinations – Aw, Cw and Dw.

s:- Dry season in the summer of the respective hemisphere (high sun season).

m:- Rainforest climate. Despite short, dry season in monsoon type of precipitation cycle. Applies to only A climates (Am).

Types of Climates

From the combination of the two letter groups, twelve distinct climates emerge as follows:

Tropical Rainforest Climate (Af): Rainfall of the driest month is 6 cm or more.

Monsoon variety of Af (Am): Rainfall of the direst month is less than 6 cm. The dry season is strongly developed.

Tropical Savanna Climate (Aw): At least one month has rainfall less than 6 cm. The dry season is strongly developed.

Steppe Climate (BS): A semi-arid climate characterized by grasslands. It occupies an intermediate position between the desert climate “BW” and the more humid climates of A, C and D groups.

Desert Climate (BW): An arid climate with annual precipitation usually less than 40 cm.

Mild Humid Climate with no dry season (Cf): Temperate rainy climate, moist in all seasons. Precipitation of the driest month averages more than 3 cm.

Mild Humid Climate with a dry winter (Cw): Temperate rainy climate with dry winter. The wettest month of summer has at least 10 times the precipitation of the driest month of winter or 70% or more of the mean annual precipitation falls in the warmer six months.

Mild Humid Climate with a dry summer (Cs): Temperate rainy climate with dry summer. Precipitation of the driest month of summer is less than 3 cm. Precipitation of the wettest month of winter is at least 3 times as much as that of the driest month of summer or 70% or more of the mean annual precipitation falls in the six months of winter.

Snowy Forest Climate with a moist winter (Df): Cold snowy forest climate with moist in all seasons.

Snowy Forest Climate with a dry winter (Dw): Cold snowy forest climate with dry winter.

Tundra Climate (ET): Mean temperature of the warmest month is above 0oC, but below 10oC.

Perpetual Frost Climate (EF):Ice-sheet climate. Mean monthly temperatures of all months are below 0oC.

Further Variations

To differentiate more variations in temperature or weather elements, Koppen added a third letter to the code group. Meanings are as follows:
a: With hot summer; warmest month over 71.6oF. Used for C and D climates.
b: With warm summer; warmest month below 71.6oF. Used for C and D climates.
c: With cold, short summer; less than 4 months over 50oF. Used for C and D climates.
d: With very cold winter; coldest month below –36.4oF. Used for D climates only.
h: Dry, hot; mean annual temperature over 64.4oF. Used for B climates only.
k: Dry, cold; mean annual temperature under 64.4oF. Used for B climates only.

Analyzed according to the Köppen system, India hosts six major climatic subtypes, ranging from desert in the west, to alpine tundra and glaciers in the north, to humid tropical regions supporting rain forests in the southwest and the island territories. Many regions have starkly different micro climates. The nation has four seasons: winter (January and February), summer (March to May), a monsoon (rainy) season (June to September), and a post-monsoon period (October to December).

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