Geoscience Reference
In-Depth Information
APPENDIX 1
Climate classification
The purpose of any classification system is to
obtain an efficient arrangement of information
in a simplified and generalized form. Climate
statistics can be organized in order to describe
and delimit the major types of climate in quantita-
tive terms. Obviously, any single classification can
serve only a few purposes satisfactorily and many
different schemes have therefore been developed.
Many climatic classifications are concerned with
the relationships between climate and vegetation
or soils and rather few attempt to address the
direct effects of climate on humans.
Only the basic principles of the four groups of
the most widely known classification systems are
summarized here. Further information may be
found in the listed references.
classification. Between 1900 and 1936, he devised
several classification schemes that involve consid-
erable complexity in their full detail. The system
has been used extensively in geographical
teaching. The key features of Köppen's approach
are temperature criteria and aridity criteria.
Temperature criteria
Five of the six major climate types are based on
monthly mean temperature values.
1
Tropical rainy climate: coldest month >18
°
C.
2
Dry climates.
3
Warm temperate rainy climates: coldest month
between -3
°
and +18
°
C, warmest month
C.
4
Cold boreal forest climates: coldest month
<-3°, warmest month >10°C. Note that many
American workers use a modified version with
0°C as the C/D boundary.
5
Tundra climate: warmest month 0-10
>10
°
A GENERIC CLASSIFICATIONS
RELATED TO PLANT GROWTH
OR VEGETATION
Numerous schemes have been suggested for
relating climate limits to plant growth or vegeta-
tion groups. They rely on two basic criteria - the
degree of aridity and of warmth.
Aridity is not simply a matter of low precipi-
tation, but of the 'effective precipitation' (i.e.,
precipitation minus evaporation). The ratio of
rainfall/temperature is often used as an index
of precipitation effectiveness, since higher
temperatures increase evaporation. W. Köppen
developed the pre-eminent example of such a
C.
6
Perpetual frost climate: warmest month <0°C.
°
The arbitrary temperature limits stem from a
variety of criteria. These are as follows: the 10
C
summer isotherm correlates with the poleward
limit of tree growth; the 18
°
C winter isotherm is
critical for certain tropical plants; and the -3
°
C
isotherm indicates a few weeks of snow cover.
However, these correlations are far from precise!
De Candolle determined the criteria in 1874 from
°
