Hot summers, cool winters, and plenty of rain. You could live in a place like this, right?
Well millions would agree with you. Because out of all the climate zones on earth, this
is the one with the largest number of highly developed world cities.
It’s the only climate zone on every inhabited continent on Earth.
And you’ve probably never heard or thought of it until now. It has been dubbed the “China”
type, the Natal type, the Southern United States type, or the Warm Temperate Eastern
Margin. But in this series we’ll call it the Humid Subtropical.
In our journey from the equator toward the poles in this series, it is now time to review
the Temperate band, where we find most of the developed world. The climate zone in this
band nearest the equator lies on the eastern boundaries of all the major continents between
about 20 and 40 degrees latitude, and is called by most climatologists the Humid Subtropical.
What defines this climate is the generous presence of rain and a hot and humid summer
where temperatures approach that of the tropics. But to distinguish it from such tropical zones,
it has a cool winter where temperatures typically drop to between zero and ten degrees celsius.
This seasonal variation is due to the increased latitude compared to the tropics. In summer
the sun is close to overhead at noon, whereas in winter, it is much closer to the horizon,
and so sunlight strikes the earth at an angle, spreading its heat over a wider area and diluting
its power. There are two subdivisions of this climate
within the Koppen Climate Classification both of which share the seasonal variation in temperature
just described, and differing only by rainfall pattern. The first, and most geographically
widespread is Cfa, which experiences rain all year round. The second, Cwa, has rain
mostly or only during the summer, and because of this similarity to the Tropical Monsoon,
this is known as the Subtropical Monsoon, owing to its cooler winter temperatures when
compared to its Tropical cousin. Now those of you paying attention in the last
episode on Hot Deserts may be saying “Wait a minute, that band just above the tropics
should be desert, due to the descending columns of air originating from the tropical uplift!”…
or something similar. So why, on the eastern edges of the continents at these latitudes
do we get a wet climate instead of desert? Well, as usual in weather and climate, the
full explanation is complex, but a simpler answer is that the oceans on the eastern fringes
of the continents have warm water compared to the western fringes that have cold water,
due to ocean current circulation. Warm ocean means lots of moist air above it, and this
is pushed onto the land by the high pressure ridge that is concentrated to the east of
each continent. When the warm moist air goes over land, it releases its moisture as rain.
By contrast, the deserts at the same latitudes have air moving over cold water onto land,
which at best produces fog, or no wind at all due to high pressure directly above them.
So where in the world do we find the Humid Subtropical climate? Well, the short answer
is, on every continent excluding Antarctica, and it’s the only climate type to claim
such an accolade. Starting as we do in the Western Hemisphere,
and moving eastward, we first encounter this climate in the south-eastern United States,
where it covers almost a quarter of the entire country. From Missouri down to Texas in the
west, across all the “southern states” out to the eastern seaboard, where it extends
north all the way to New York City in the north and to all but the southern coast of
Florida in the south. Further south on this continent, in Mexico, there are two bands
of the monsoonal variant lying on each side of the central highlands.
In South America, we find another large stretch of the middle eastern part of this continent
dominated by the Humid Subtropical. From south-eastern Brazil, including its largest city Sao Paolo,
this region stretches out to encompass most of Paraguay, all of Uruguay, and the most
populated regions of north eastern Argentina, including its capital Buenos Aires.
With this climate, we see our first entry into the continent of Europe. Specifically,
in the northern and eastern parts of Italy, sheltered around the Alps to the north and
the Apennine mountains to the south, we have humid summers and cool winters instead of
the Mediterranean climate that otherwise dominates the larger region - more on that one in the
next episode. Pockets of this climate type occur further east in the Balkans, along with
some of the coasts of the Black Sea. In Africa, we find a band across the southern
part of the continent under the influence of the Cwa monsoon variant of this climate,
while in the extreme south east, in the Kwazulu- Natal region of South Africa, we get the all
year round rain of the Cfa type. In Asia, the Cwa monsoonal variant dominates
a large stretch of northern India, including the capital of Delhi and most of the heavily
populated Ganges river system. This band of the subtropical monsoon extends eastward into
northern Vietnam and southern and mid China including the hugely populated Pearl River
Delta, with cities such as Guangzhou, Shenzhen, Macau and Hong Kong.
The Cfa year-round rain variant in Asia occurs over a wider area in the main part of central
and eastern China, including a host large cities such as the megacity of Shanghai. Moving
off the coast of that continent, we have the whole of Taiwan, and the southern and eastern
parts of Japan that form the major population centres of that nation, including the world’s
largest urban area of Tokyo, that nation’s capital.
The last continent which has the Humid Subtropical climate is Australia, specifically the central
eastern coast, including the cities of Brisbane, and that nation’s largest city – Sydney.
Despite its dispersal across all continents of the globe, the Humid Subtropical climate
is proven as a particular and consistent type by comparing temperature and rainfall graphs
across each of these areas.
So what kind of landscapes and vegetation do we find in the Humid Subtropical climate?
Low lying plains are the most common type of topography in this climate zone, and in
their natural state, such plains would be covered by either mixed woodland or grassland.
Being a temperate climate, this is the first that we see with four distinct seasons, easily defined
by the deciduous trees that mark this zone, whether in their natural habitat or included
within the cities here – blossom in spring, green leaves in summer, the yellow and red
falling leaves of autumn and bare in winter. Because this moderate climate favours a diverse
array of crops, however, most of it has given way to agriculture – rice, nuts, wheat,
ranching, cotton, tobacco depending upon the region.
With its relatively mild temperatures and plentiful rain supporting so much agriculture,
high populations can be supported, especially the rice-supporting regions in China and India,
meaning this climate zone is home to more people than any other. And being in one of
the cities of the Humid Subtropical, under more tolerable conditions compared to the
tropics, allows for large and sophisticated cities to develop on every continent – again
more than any other climate type. And here’s just a sample of them…
So that’s it for the Humid Subtropical climate zone. It might not be as exotic as others
we’ve covered so far, yet its importance in terms of population and cities across such
a wide stretch of the globe cannot be overstated. If you enjoyed the video, please share with
your friends and don’t forget to subscribe to this YouTube channel so you don’t miss
future episodes. You can also help support the making of these documentaries by subscribing
to my Patreon channel, a link to which can be found in this video’s accompanying text.
And do leave some comments, particularly if you live or have lived in one of the many
cities of the Humid Subtropical climate.
Thanks again for watching, and I’ll see you in the next episode, where we’ll be
headed for the summer sun of the Mediterranean climate zones. Until then, bye for now!