Koeppen Climate Classification

The Koeppen model (Koeppen 1938; as modified by Guetter and Kutzbach 1990) was designed for climate classification work, however, it also allows for a prediction of the vegetation growing at a particular site (originally the classification scheme was designed so that climate boundaries corresponded with major vegetation boundaries). The climate classification (in the modified form), name for the climate group, and typical potential natural vegetation for the climate group are provided in the output. All you need to do is: 1) make sure the program classifies the climate correctly; and 2) compare the predicted vegetation to the actual potential natural vegetation for the site.

Category	Description
A	Tropical rainy climates: No winter; annual precipitation exceeds evapotranspiration; mean temperature of every month greater than 18°C
B	Dry climates: Evaporation exceeds precipitation throughout year; boundaries of B climates are determined by ratio of mean annual temperature to mean annual precipitation.
C	Mild, humid climates: At least one month has a mean temperature greater than 10°C; mean temperature of coldest month between -3°C and 18°C.
D	Snowy-forest climates: mean temperature of warmest month greater than 10°C; mean temperature of coldest month less than or equal to -3°C.
E	Polar climates: Cold climates with no summer; mean temperature of warmest month less than 10°C.

The five primary categories can be further subdivided into secondary and teritiary groupings, depending on the primary category.

Category	Description
	The A climates can be subdivided into three secondary categories:
f	Tropical rainforest climates: Precipitation for each month greater than 60 mm in Af climates.
m	Monsoon climates: Strong dry season with precipitation for at least one month less than or equal to 60 mm; boundary between Am and Aw climates determined by ratio of annual precipitation to precipitation of driest month.
w	Savanna climates: Winter dry season; precipitation less that than in Am climates; boundary between Am and Aw climates determined by ratio of annual precipitation to precipitation of driest month.
	Polar climates: Cold climates with no summer; mean temperature of warmest month less than 10°C.

	The B climates can be subdivided into two secondary categories:
S	Steppe climates: Boundary between BS and BW climates determined by ratio of mean annual temperature to mean annual precipitation. BS climates are wetter than BW climates.
W	Desert climates: Boundary between BS and BW climates determined by ratio of mean annual temperature to mean annual precipitation. BW climates are drier than BS climates.

	C and D climates can be subdivided into three secondary categories:
f	Moist climates: Precipitation more or less evenly distributed throughout year in Cf/Df climates.
s	Summer dry season climates: In the original classification, s would designate a climate in which the mean precipitation of driest summer month is less than one-third that of wettest winter month in Cs/Ds climates. For tropical latitudes, ClimVegWin uses an alternative calculation in which less than 30 percent of the average annual precipitation falls within the six high-sun (summer) months.
w	Winter dry season climates: In the original classification, w would designate a climate in which the mean precipitation of the driest winter month is less than one-tenth that of wettest summer month in Cw/Dw climates. For tropical latitudes, ClimVegWin uses an alternative calculation in which less than 30 percent of the average annual precipitation falls within the six low-sun (winter) months.

	E climates can be subdivided into three secondary categories:
T	Tundra climates: Mean temperature of warmest month less than or equal to 10°C but greater than 0°C
F	Ice cap climates: Mean temperature of warmest month less than or equal to 0°C.

Some Koeppen climate types (B, C and D) can be further subdivided into tertiary categories:

Category	Description
	The B climates have two tertiary categories:
h	Hot climates: Mean annual temperature greater than 18°C (BSh, BWh).
k	Cold climates: Mean annual temperature less than or equal to 18°C (BSk, BWk)

	C and D climates have as many as four tertiary categories:
a	Hot summer climates: Mean temperature of warmest month greater than 22°C (Cfa, Dfa, Csa, Dsa, Cwa, Dwa)
b	Warm summer climates: Mean temperature of warmest month less than or equal to 22°C, but at least four months have mean temperatures greater than 10°C (Cfb, Dfb, Csb, Dsb, Cwb, Dwb).
c	Cool summer climates: Mean temperature of warmest month less than or equal to 22°C (Cfc, Dfc, Csc, Dsc, Cwc, Dwc).
d	Severe winter climates: The severe winter categorie applies to D climates alone; mean temperature of the coldest month is less than or equal to -38°C (Dfc, Dsc, Dwc).

The modified Koeppen climate classification system (Guetter and Kutzbach 1990) includes the same categories, with one exception -- there is no Am climate, only Af and Aw climates. The primary difference is some of the cutoff criteria between some of the primary or secondary categories.

In the modified system, A climates are defined as having the mean temperature of every month greater than 16°C rather than 18°C. In Aw climates, precipitation for at least one month less than or equal to 40 mm. Otherwise, the climate is classified as Af.

The boundary between C and D climates in the modified system is lower than in the original system. C climates are defined as having a mean temperature of the coldest month greater than -5°C rathern than -3°C.

E climates are defined by the modified system as having a mean temperature of the warmest month less than or equal to 11°C rather than 10°C.

For more information see Oliver and Wilson (1987), Strahler and Strahler (1989; pp. 164-169) and Guetter and Kutzbach (1990).