Classification of Global Climates
Climate is the characteristic conditions of the atmosphere near the earth's surface at a given place or over a
given region. Climate represents a generalization of weather. Weather conditions accumulated over many
years time. Concern on mean, average values and the departures from those means and the probabilities
that such departures will occur. Components include net radiation, sensible heat, barometric pressure,
winds, relative and specific humidity, dew point, cloud cover, fog, precipitation type, and intensity,
evaporation and transpiration, incidence of cyclones and anticyclones, and frequency of frontal passages.
I. Climate and Life:
Define environmental regions of significance to man and to all life. Plant life is exposed to the atmosphere
for exchanges of energy and matter.
II. Climate Classification:
Goal: Atmospheric components essential to life on the lands. Energy and water are the most important
components to life. Global distribution pattern -- geographic.
1. Net Radiation as a Basis of Climate Classification Werner H. Terjung in 1970 used insolation or net
radiation as the basis of a global classification of climates. Net radiation is regarded as the best indicator of
energy available for plant growth, along with a measure of available water in the form of soil moisture.
2. Temperature as a Basis of Climate Classification Using monthly mean air temperature:
(1) Winterless climates of low latitudes. >64.4 F (18 C)
(2) Climates with both a summer and a winter season.
(3) Summerless climates of high latitudes. <50 F (10 C)
3. Precipitation as a Basis for Climate Classification
Isohyete: equal amount of precipitation connected by lines to show world and regional
World precipitation regions:
(1) Wet equatorial belt -- mE, Amazon, Congo >80"
(2) Trade-wind coasts -- mT, 60-80"
(3) Tropical deserts -- cT,
(4) Middle-latitude deserts and steppes -- cT, cP,
(5) Humid subtropical regions -- mT,
(6) Middle-latitude west coasts -- mP,
(7) Arctic and Polar deserts -- cP, cA.
4. The Soil Moisture Balance as a Basis for Climate Classification:
Based upon: precipitation and evaportranspiration availability of water for plants.
5. Vegetation and Soils as Bases of Climate Classifications:
Plants are highly responsive to differences in climate. They (vegetation and soil) reflect and
response the differences in climate but do not cause those differences.
6. An Explanatory-Descriptive Climate System:
Explanatory-Descriptive approach: explain genesis and origin of the phenomena
III. The Koppen Climate Classification System:
Combine temperature and precipitation characteristics fitted into known vegetation and soil distributions
were carried out in 1918 by Wladimir Koppen of the University of Graz in Austria. Groups A, C, D, have
sufficient heat and precipitation for growth of high-trunk trees (forest and woodland vegetation).
A: Tropical climates - every month > 64.4 F (18 C) no winter season, P>E
B: Dry climates - PE>P, no water surplus, no permanent streams
C: Warm temperate (mesothermal) climates - coldest month <64.4 F and >26.6 F,
summer and winter season. At least 1 warm month >50 F
D: Snow (microthermal) climates: Coldest month <26.6 F (-3 C), warmest month >
50 F (10 C)
E: Ice climates - warmest month < 50 F (10 C), no true summer
S: Steppe climate - semi-arid climate, 15-30" rainfall a year.
W: Desert climate - Arid climate, <10"
f: Moist, no dry season, applied to A, C, D.
w: Dry season in winter.
s: Dry season in summer.
m: Rainforest climate despite short, dry season in Monsoon area
Eleven distinct climates emerges as follows:
Af: Tropical Rainforest (Am - a variant of Af)
Aw: Tropical Savanna
BS: Steppe climate
BW: Desert climate
Cw: Temperate rainy (humid mesothermal) climate with dry winter.
Cf: Temperate rainy (humid mesothermal) climate moist all seasons.
Cs: Temperate rainy climate with dry summer.
Df: Cold snowy forest (humid microthermal) climate moist in all seasons.
Dw: Cold snowy forest (humid microthermal) climate with dry winter.
ET: Tundra climate
EF: Climates of perpetual frost (ice caps)
a: with hot summer; warmest month >71.6 F (22 C) - C, D
b: with warm summer; warmest month<71.6 F (22 C) - C, D
c: with cool, short summer; less than 4 months over 50 F
d: with very cold winter; coldest month below -36.4 F (- 38 C) - in D climate
h: Dry-hot; mean annual temperature over 64.4 F - B
k: Dry-cold; mean annual temperature under 64.4 F - B
BWk: cool desert climate
Dfc: cold, snowy forest climate with cool, short summer.
Air Mass Source Regions and Frontal Zones as a Basis of Classification:
Group I: Tropical air mass source regions and the equatorial trough or convergence zone between.
Controlled by the dynamic subtropical high-pressure cells, or anti- cyclones, regions of air subsidence and
are dry. Af, Am, BWh, BSh, BWk, BWh, Aw, Cwa.
Group II: Zone of intense interactions between unlike air masses: the polar front zone and tropical
air masses. Cfa, Cfb, Cfc, Csa, Csb, BWk, BWh, BSh, BSk, Dfa, Dfb, Dwa, Dwb.
Group III: dominated by polar and arctic air masses. Dfc, Dfd, Dwc, Dwd, ET, EF.