Geoscience Reference
In-Depth Information
W. Lauer
et al
. (1996) have prepared a new
classification and map of world climate types
based on thermal and hygric thresholds for both
natural vegetation and crops. The limits of the
four primary zones (tropical, subtropical, mid-
latitude and polar regions) are determined from
a radiation index (duration of daily sunshine
hours). Climate types are then based on a thermal
index (temperature sums) and a moisture index,
which takes account of the difference between
monthly precipitation and potential evaporation.
A. N. Strahler (1969) proposed a simple but
effective genetic classification of world climates,
based on the fundamental planetary mechanisms.
Following a tripartite division by latitude (low,
middle and high), regions are grouped according
to the relative influence of the ITCZ, the sub-
tropical high pressure cells, cyclonic storms, high-
latitude frontal zones and Polar/Arctic air sources.
This gives 14 classes and a separate category of
Highland Climates. Briefly, these are as follows:
1
Low-latitude climates controlled by equatorial
and tropical air masses.
•
C GENETIC CLASSIFICATIONS
The genetic basis of large-scale (macro-) climates
is the atmospheric circulation, and this can be
related to regional climatology in terms of wind
regimes or air masses.
H. Flohn proposed one system in 1950. The
major categories are based on the global wind
belts and precipitation seasonality, as follows:
1
Equatorial westerly zone: constantly wet.
2
Tropical zone, winter trades: summer rainfall.
3
Subtropical dry zone (trades or subtropical
high pressure): dry conditions prevail.
4
Subtropical winter-rain zone (Mediterranean
type): winter rainfall.
5
Extra-tropical westerly zone: precipitation
throughout the year.
6
Subpolar zone: limited precipitation through-
out the year.
6a
Boreal, continental subtype: summer rainfall;
limited winter snowfall.
7
High polar zone: meagre precipitation;
summer rainfall, early winter snowfall.
Wet equatorial climate (10°N-10°S; Asia
10
N) - converging equatorial and
mT air masses produce heavy convectional
rains; uniform temperature.
°
S-20
°
•
Trade Wind littoral climate (10
N
and S) - high-sun Trade Winds alternate
seasonally with subtropical high pressure;
strong seasonality of rainfall, high
temperatures.
°
-25
°
•
Tropical desert and steppe (15°-35°N and
S) - dominance of subtropical high pressure
gives low rainfall and high maximum
temperatures with moderate annual range.
•
West Coast desert climate (15
N and S)
- dominance of subtropical high pressure.
Cool seas maintain low rainfall with fog and
small annual temperature range.
°
-30
°
•
Tropical wet-dry climate (5
N and S)
- high-sun wet season, low-sun dry season;
small annual temperature range.
°
-15
°
2
Mid-latitude climates controlled by both
tropical and polar air masses.
•
Humid subtropical climate (20
N and
S) - high-sun moist mT air and low-sun
cyclones give well-distributed annual rain-
fall with moderate temperature regime.
°
-25
°
Temperature does not appear explicitly in the
scheme.
Figure A1.2B
shows the distribution of
these types on a hypothetical continent. Rough
agreement between these types and those of
Köppen's scheme is apparent. Note that the boreal
subtype is restricted to the Northern Hemisphere
and that the subtropical zones do not occur on the
eastern side of a land mass. Flohn's approach has
value as an introductory teaching outline.
•
West Coast marine climate (40
N and
S) - windward coasts with cyclones all year.
Cloudy; well-distributed rainfall with low-
sun maximum.
°
-60
°
•
Mediterranean climate (30
N and
S). Hot, dry summers associated with the
°
-45
°
