In pretty much every area of interest, human beings love to put things into boxes.
They love to categorise and classify.
From artistic subjects such as music and literary genres, to science including stars, chemical
elements and animals.
Our planet’s climate is no exception to this.
And one at first might ask why is it necessary to put a label on weather patterns from one
part of the globe to another.
Knowing the patterns of temperature and rainfall is important mostly for understanding how
the earth can support population in that area through farming.
But general knowledge of this also impacts on other areas such as tourism and migration.
Regardless, humans will be humans, and in the absence of any perceived application to
such knowledge will still classify, for the love of science, or to improve understanding.
The primary classification of earth climate is known as the Koppen-Geiger system.
It has evolved over the past 150 years to define precisely the nature of weather patterns
on every part of our planet.
Each of these climate zones has been covered in detail in my previous series – Secrets
of World Climate, in which I show real places in each climate zone and explain why the patterns
of rainfall and temperature are the way they are.
In this new series, I’ll be picking up on aspects of global and local climate that transcend
these zones, case by case, in what will be known as the Climate Casebook.
The first in this series is intended as a quick reference work, summarising each of
the Koppen Zones, so that in the episodes that follow, anyone new to the subject can
get a quick grasp of what on earth I’m talking about.
If you want to find a specific section, I’ve provided video bookmarks in the accompanying text.
Overall, the Koppen-Geiger system has five broad categories, which describe a general
pattern and roughly start at the equator and end at the pole.
These are always the capital first letter of the shorthand codes that every climate
zone has, and are as follows.
A. TROPICAL – the zones around the equator, which are hot all year round and either have
heavy rain all year round or during some part of the year.
B. DRY – subtropical or continental areas with very little rain year round.
C. TEMPERATE – areas which have relatively mild temperature ranges year round, and occurring
at the mid-latitudes near coasts.
D. CONTINENTAL – areas of high temperature ranges occurring usually deep within the northern
continents, experiencing cold or very cold winters.
E. POLAR – areas which are cold all year around, occurring near or at the poles of our planet.
Each of these broad categories is further subdivided, to account for more precise differences
in temperatures or rainfall, and these give us the full two or three digit Koppen-Geiger codes.
These codes at first might seem like they’re just hieroglyphics, but a quick look can reveal
the logic on 80% of them.
In all the temperate and continental codes, the second letter tells us when there is a dry season.
“s” means the dry season is in summer, “w” the dry season is winter,
and “f” for no dry season at all.
The third letter tells us how warm or hot it is, with “a” being the hottest and
“d” being the coldest.
So, armed with this knowledge, lets get straight into looking at each and every one of the
Koppen zones.
Af – The Tropical Rainforest, also known as the Equatorial Climate, or Selva (which
is Spanish for “jungle”).
Occurring only within the tropics at low elevations, the key defining characteristic of this climate
is rain and hot temperatures all year round.
This produces the famous rainforest that the zone is named after and the largest biodiversity
on Earth.
Am – The Tropical Monsoon.
Found also exclusively within the tropics, this climate zone experiences heavy rain during
part or most of the year, but also has a relatively short dry, or longer drier season, due to
the shifting direction of trade winds from land to sea and vice versa.
Aw – Tropical Savannah.
A close sibling of the Tropical Monsoon, and covering much larger areas in the tropics,
here the dry season is either completely dry, or is dry over a longer period.
Both the Savannah and Monsoon have a mix of woodland and grassland depending upon the
amount of rain and local topography.
Both support enormous populations and many large cities due to the combination of heat
and rainfall without the human health issues of the rainforests.
BWh – Hot Desert.
Lying on the border of the tropics, these areas experience very little rain, and searing
summer temperatures which hold the records for the highest on Earth.
Little or no vegetation exists here, with only bare rock and sand as landscape.
BSh – Hot Semi Arid.
Lying next to Hot Deserts, these areas have a little more rain to support scrub-like vegetation
but are still marginal in terms of sustainable human settlement.
BWk – Cool Desert.
Lying deep within the continents far from the ocean, or on the leeward side of mountains
sheltering them from moist winds, these areas are as parched and desolate as the hot deserts,
but experience winter temperatures that often fall below freezing point.
BSk – Cool Semi Arid.
Like the Cool Deserts only with more rain, but not enough to be classified as temperate
or continental.
Like their Hot Semi-Arid counterparts, they support shrub-like vegetation or hardy grasses.
Cfa – Humid Subtropical.
Lying at a similar latitude to the Hot Deserts, these areas on the eastern fringes of the
continents, however, are next to warm oceans that bring in plenty of moisture.
They experience tropical summers, but cool winters, and rain all year round.
They are among the most important areas for human civilisation, housing enormous populations
and many great world cities.
Typical natural vegetation ranges from forest to swamp and grassland, but much of these
areas have been given over to farming.
Cwa – Subtropical Monsoon.
A sibling of the Humid Subtropical, and found mainly in Asia at the same latitudes, this
varies only in that it has a winter dry season instead of rain year round due to the presence
of the Asian Monsoon.
Csa – Hot Summer Mediterranean.
Lying just above the Hot Deserts in latitude, and always on the western fringes of continents,
these areas experience the hot and dry conditions of deserts in summer, but significant rain
from oceanic westerly winds in winter.
Natural vegetation is limited by the desert-like conditions of summer, and is typically shrub-like.
Csb – Warm Summer Mediterranean.
Always lying above their Csa siblings on the continental western coasts, these areas have
warm dry summers instead of hot, and usually even heavier rainfall in winter.
With less harsh winters, natural vegetation is usually in the form of coniferous forest,
including the Redwoods and Sequoias of California, the tallest in the world.
Cwb – Subtropical Highland.
Occurring in tropical latitudes, the heat of the rainforest and savannah is reduced
significantly through being at high altitude.
The result is year round mild temperatures, with a pronounced dry season.
Found mainly in Latin America, East Africa and the foothills of the Himalayas.
Natural vegetation is a mix of forest and grassland.
Cwc – Cool Subtropical Highland.
At even higher altitudes in the tropics, the mild temperatures of its sibling Cwb zone
gives way to noticeably chilly weather, year round.
It is not common.
Cfb – Oceanic and Subtropical Highland.
One of the more confusing Koppen codes, due to an accident of nature creating very similar
conditions for completely different reasons.
Small upland areas near the equator, such as in Colombia and Ecuador, have this mild
year round climate which also experiences rain year round.
But over much larger areas in mid-latitudes, this climate exists next to western coasts,
where prevailing westerlies moderate temperatures year round such that warm summers and cool
winters are the norm.
In both cases, limited seasonal temperature range and year round rain are its defining hallmark.
Natural vegetation is mixed woodland, but these areas are heavily farmed.
Cfc – Subpolar Oceanic.
lying in certain areas higher in latitude or elevation to the Oceanic, these areas still
have mild winters, but cooler summers.
Dfa/Dfb – The first of the six Continental climates, occurring only within the great
land masses of the Northern Continents.
All these climates experience high temperature ranges between summer and winter, and all
have cold winters, routinely falling below freezing.
These first two experience rain year round, with Dfa experiencing hot summers, and Dfb
experiencing somewhat cooler but still warm summers, and are the most prevalent, occurring
across wide continental areas.
Natural vegetation is usually in the form of grassland, but these areas are heavily farmed.
Dwa/Dwb – The same as Dfa/Dfb except that there is little to no rain during the winter.
These occur exclusively in Eastern Asia due to the influence of the Asian Monsoon.
Dsa/Dsb – The same as the other Continental climates, except that the summer is dry instead
of winter.
These areas are not common, and usually occur inward from Mediterranean climate areas.
Dfc/Dfd – The first of the six Subarctic climates.
These areas, lying to the north of and similar to the Continental climates, except winters
are much, much colder.
These two zones have rain or snow year round.
Like all the subarctic zones, the vegetation is dominated by coniferous forest, known by
the Russian word "Taiga", and farming is almost non-existent.
Dwc/Dwd – These Subarctic zones are identical to the first two except they have dry winters
– they occur only in Eastern Siberia.
Dsc/Dsd – These very rare Subarctic zones are like the others except that the dry season
occurs in summer.
ET – Tundra.
Even further North than the Subarctic, the true Arctic has the treeless waste of the
Tundra, where summer temperatures are just too cold to support tree growth, a situation
compounded by the presence of permanently frozen soil just below the surface, known as permafrost.
Only hardy grasses and shrubs survive here.
Tundra also occurs in comparatively small alpine areas, and around the Straights of
Magellan between South America and Antarctica.
EF – Icecap.
Below freezing point all year round, these areas produce ice sheets several kilometres
thick and are confined to Greenland and Antarctica.
Nothing can grow in these harshest of conditions.
So that was your rapid-fire summary of the Koppen Climate Zones of Earth.
I hope you found it useful in introduction to this system, or to link the various zones
together into a general pattern for understanding.
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I’ll see you in the next of the Climate Casebook series.