A humid subtropical climate is a zone of subtropical climate characterized by hot, humid summers
and generally mild winters. Under the Köppen climate definition, this category of climate
type covers a broad range of attributes, especially in terms of winter temperatures. Under the
more modern Trewartha climate classification, most of the climates that have 8 or more months
with a mean temperature of 10 C are warm to hot much of the year with mild winters.
Description The Köppen definition of this climate is
for the coldest month's mean temperature to be between −3 °C and 18 °C, and the
warmest month to be above 22 °C. Some climatologists prefer to use 0 °C as the lower bound for
the coldest month's mean temperature. It is either accompanied with a dry winter — or
has no distinguished dry season. Under the more modern Trewartha climate classification,
climates are termed Humid Subtropical when they have mean temperatures of 10 C for eight
or more months a year. In most locations classed within this system, the mean temperature of
the coldest month is between 3 C and 18 C. Some climatologists consider the Trewartha
grouping of subtropical climates to be more real-world and fitting on a global scale.
Rainfall in humid subtropical climates often shows a summer peak, and where monsoons are
well developed, like Southeast Asia, a strong summer peak and winter drought is common.
Due to the influence of the subtropical highs and subsidence, droughts can be severe and
often catastrophic to agriculture. Winter rainfall is associated with large storms and
fronts that the westerlies steer from west to east, that on occasion reach down into
subtropical latitudes. Most summer rainfall occurs during thunderstorms and weak tropical
lows that move in from adjacent warm tropical oceans.
Overview of distribution Humid subtropical climates normally lie on
the southeast side of all continents, generally between latitudes 25° and 40° north and
tend to be located at coastal or near coastal locations. However, in some cases the climate
extends well inland, most notably in China and the United States.
Africa In Africa, the humid subtropical climates
are found in two separate areas on the southern hemisphere of the continent. The Cwa climate
is found over a large portion of the interior of the Middle and Eastern African regions.
This area includes; central Angola, northeastern Zimbabwe, the Niassa, Manica and Tete provinces
of Mozambique, the southern Congo provinces, southwest Tanzania, and the majority of Malawi,
and Zambia. Some lower portions of the Ethiopian Highlands also have this climate. The climate
is also found in the narrow coastal sections of southern and eastern South Africa, primarily
in KwaZulu-Natal and the Eastern Cape provinces. South Africa's version of this climate features
heavy oceanic influences resulting in generally milder temperatures. This is particularly
evident in its winters when temperatures do not drop as low as in many other regions within
the humid subtropical category. Asia
Locations in Asia with a humid subtropical climate differ from those in other continents
in that they often have marked seasonal differences in precipitation, if not very dry winters.
East Asia In East Asia, this climate type is found in
the southeastern quarter of mainland China, the northern half of Taiwan, northern Vietnam,
narrow areas along the coast of South Korea, and Japan. Cities near the equatorward boundary
of this zone include Hong Kong, Hanoi and Taipei while Qingdao is near the northern
boundary. The influence of the strong Siberian anticyclone
in East Asia brings colder winter temperatures southward, pushing the 0 °C isotherm as
far south as the valleys of the Yellow and Wei, roughly latitude 34° N. At Hainan Island
and in Taiwan, the climate transitions from subtropical into fully tropical. In most of
this region, there is extremely limited precipitation during the winter, owing to the powerful anticyclonic
winds from Siberia. Only in inland areas below the Yangtze River and coastal areas between
approximately the Huai River and the beginning of the coast of Guangdong is there sufficient
winter rainfall to produce a Cfa climate; even in these areas, rainfall and streamflow
display a highly pronounced summer peak, unlike other regions of this climate type. The only
area where winter precipitation equals or even exceeds the summer rain is on the "San-in",
or western, coast of Japan, which during winter is on the windward side of the westerlies.
The winter precipitation in these regions is usually produced by low-pressure systems
off the east coast that develop in the onshore flow from the Siberian high. Summer rainfall
comes from the East Asian Monsoon and from frequent typhoons. Annual rainfall is generally
over 1,000 millimetres, and in areas below the Himalayas can be much higher still.
South Asia Humid subtropical climates can also be found
in South Asia, primarily along the Ganges River. However, the humid subtropical climates
exhibited here differ markedly from humid subtropical climates in East Asia. Winters
here are typically mild, dry and relatively short. They also tend to be foggy. Summers
tend to be long and very hot, starting from mid-April and peaking in May and early June
with high temperatures often exceeding 40 °C. They also tend to be extremely dry, complete
with dust storms, traits usually associated with arid or semiarid climates. During this
period many native trees defoliate to save water. This is followed by the cooler monsoons,
where the region experiences heavy rains on almost a daily basis. Average high temperatures
decreases during the monsoon season but the humidity increases. This results in hot and
humid conditions, similar to summers in humid subtropical climates. Cities such as New Delhi,
Lucknow, Kanpur and Patna exhibit this atypical version of the climate in India. In Pakistan,
the twin cities of Rawalpindi/Islamabad also feature this weather pattern, but with wetter
and relatively cooler winters. In South Asia, humid subtropical climates
generally border on continental climates as altitude increases, or on winter-rainfall
climates in Pakistan. Further east, in highland areas with lengthier monsoons such as Nepal,
seasonal temperature variation is lower than in the lowlands.
Southwestern Asia Although humid subtropical climates in Asia
are mostly confined to the southeastern quarter of the continent, there are areas on the Caspian
Sea and Black Sea with humid subtropical climates that are unusually warm for their high latitudes
and also unusual for this climate type, that snowfall in winter is relatively common, but
is usually of a short duration. In Southwestern Asia, the climate is prevalent
in the Gilan of Iran, in parts of the Caucasus, in Azerbaijan and in Georgia wedged between
the Caspian and Black seas. The climate is also present in small areas of the southern
Russian Federation and coastal Turkey. In the narrow Caspian coastal strip of Iran,
a humid subtropical climate prevails . Annual rainfall ranges from around 740 mm at Sari
to over 2,000 mm at Bandar-e Anzali, and is heavy throughout the year, with a maximum
in October or November when Bandar-e Anzali can average 400 millimetres. Temperatures
are generally moderate in comparison with other parts of Southwestern Asia. In Rasht,
the average maximum in July is around 28 °C but with near-saturation humidity, whilst
in January it is around 9 °C. The heavy, evenly distributed rainfall extends north
into the Caspian coastal strip of Azerbaijan up to its northern border but this climate
in Azerbaijan is, however, a Cfb/Cfa borderline case. During winter, the coastal areas can
receive snowfall, but is usually of a short duration. Annual rainfall in Lankaran in the
southeast averages up to 1,800 mm and is heavy throughout the year; and annual rainfall
is generally over 1,000 mm in the foothills of the Caucasus in the northeast, as altitude
increases and the humid subtropical climate changes to the oceanic climate
Western Georgia in the Kolkheti Lowland and the north coast of Turkey, have a climate
similar to that of Gilan and Mazandaran in Iran and very similar to that of southeastern
and northern Azerbaijan. Temperatures range from 22 °C in summer to 5 °C in winter
and rainfall is even heavier than in Caspian Iran, up to 2,300 millimetres per year in
Hopa and up to 2,718 millimetres per year in Batumi falling throughout the year. This
climate in northern Turkey and western Georgia is, again, a Cfb/Cfa borderline case. Again,
during winter, the coastal areas can receive snowfall, which is usually of a short duration.
North America
In North America, humid subtropical climates are almost exclusively the domain of the American
Gulf and south Atlantic states, including the following states: the eastern half of
Texas, Oklahoma, Louisiana, Arkansas, Alabama, Mississippi, North Carolina, South Carolina,
Virginia, Tennessee, Georgia, and Florida. On the Florida peninsula, the humid subtropical
climates gives way to the tropical climate of south Florida and the Florida Keys. In
the U.S., the archetypal humid subtropical climate is best exemplified by a city like
Savannah, Georgia - where summers are long and almost tropical, and winters are mild
with temperatures reaching freezing on only a few nights. Summers in this zone are hot
and humid, with daily averages above 25 °C with average daily maxima above 30 °C.
Under Koppen's climate classification, the humid subtropical climate can also be found
in the Mid-Atlantic, primarily Maryland, Delaware, Washington, D.C., southeastern Pennsylvania,
southern New Jersey and far southern New York, specifically New York City and Long Island.
It can also be found in the Midwest, primarily in the central and southern portions of Kansas
and Missouri, and far southern portions of Illinois, Indiana and Ohio. However, under
the newer Trewartha climate classification, virtually none of these areas would qualify
as a humid subtropical climate, as many of these areas do not feature at least eight
months of average monthly temperatures of at least 10 °C.
In Mexico, there are small areas of Cfa and Cwa climates. The climate can be found small
areas scattered around the northeastern part of the country, in proximity to the Gulf of
Mexico. Other areas where the climate can be found is in the high elevations of Trans-Mexican
Volcanic Belt and Sierra Madre Oriental. Despite being located at higher elevations, these
locations have summers that are too warm to qualify as a subtropical highland climate.
Guadalajara’s climate is a major example of this.
Characteristics and variants Outside of isolated sections of Mexico, the
southernmost limits of this climate in North America lie just north of South Florida and
around southern coastal Texas. Cities at the southernmost limits, such as Orlando and Tampa
and along the Texas coast around Brownsville generally feature warm weather year round
and minimal temperature differences between seasons. These cities fall just short of having
a true tropical climate. In contrast, cities at the northernmost limits
of the humid subtropical region, such as New York City, Philadelphia, and Louisville, Kentucky
have average winter temperatures at the coldest limit of climates classed as subtropical.
These cities experience colder winters than subtropical climates to the south.
Snowfall varies greatly in this climate zone. In locations at the southern limits of this
zone and areas around the Gulf Coast, cities such as Orlando, Tampa, Houston, New Orleans,
and Savannah rarely see snowfall, which occurs, at most, a few times per generation. In Southern
cities farther north or inland, such as Birmingham, Atlanta, Memphis, Little Rock, Nashville,
Dallas, Norfolk, Charlotte, and Raleigh, snow typically falls once or twice a season and
is usually three inches or less. Ice storms are not unusual at these locations. However
for the majority of the winter here, temperatures remain above or well above freezing. At the
northernmost limits of this zone, cities such as New York City and Philadelphia typically
see snowfall during the winter, with occasional heavy snowstorms. Still, average temperatures
during a typical winter hovers just above freezing at these locations.
Precipitation is plentiful in the humid subtropical climate zone in North America - and tends
to be concentrated in the six warmer months. Inland areas in the south tend to have precipitation
spread evenly throughout the year, while there is a semblance of a monsoon pattern along
the Atlantic coast from southern North Carolina south to Florida. The seasonal monsoon is
much stronger on the Florida peninsula, as most locations in Florida have dry winters
and wet summers. In addition, areas in Texas that are slightly inland from the Gulf of
Mexico, such as Austin and San Antonio that border the semi-arid climate zone, generally
see a peak of precipitation in the spring, and a drought-like nadir in mid-summer.
South America Humid subtropical climates are found in a
sizeable portion of South America. The climate extends over a few states of southern Brazil,
including Paraná, into sections of Paraguay, all of Uruguay, and the Río de la Plata region
in Argentina. Major cities such as São Paulo, Buenos Aires, Porto Alegre and Montevideo
have a humid subtropical climate, generally in the form of hot humid summers and mild
to cool winters. These areas, which include the Pampas, generally feature a Cfa climate
categorization. The Cwa climate occurs in parts of tropical
highlands of São Paulo state, Minas Gerais and near the Andean highland in northwestern
Argentina. These highland areas feature summer temperatures that are warm enough to fall
outside the subtropical highland climate category.
Australia The humid subtropical climate dominates half
of eastern Australia. This zone contains the only regions where
soils are not acutely deficient in phosphorus, as well as the heaviest rainfall south of
the Tropic of Capricorn, making it prime agricultural country, centred on towns such as Coffs Harbour,
Grafton, Kempsey, Port Macquarie, Tamworth, and Moree.
Variations in Australia There is variation in climate within this
zone. Annual rainfall on the coast can reach as high as 2,000 mm in favourable locations
and is generally above 1,000 mm. However, because most of the heaviest two- and three-day
rainfalls in the world occur in this coastal zone as a result of east coast lows forming
to the north of a large high pressure system, there can be great variation in rainfall from
year to year. At Lismore in the centre of this zone, the annual rainfall can range from
less than 550 mm in 1915 to more than 2,780 mm in 1950. There is usually a distinct summer
rainfall maximum that becomes more pronounced moving northwards: in Brisbane the wettest
month receives five times the rainfall of the driest. Temperatures are very warm to
hot but not excessive: the average maximum in February is usually around 29 °C and
in July around 21 °C. Frosts are extremely rare except at higher elevations, but temperatures
over 35˚C are not common on the coast. North of the Cfa climate zone there is a zone
centred upon Rockhampton and extending up to the Atherton Tableland of Köppen Cwa climate.
This has a very pronounced dry winter with often negligible rainfall between June and
October, and winter temperatures generally only slightly below 18 °C, above which one
would have a tropical savanna, or Aw, climate. Europe
Humid subtropical climates are located in the transitional area between the oceanic,
mediterranean and continental climates in southern Europe, in the areas where summer
precipitation and winter temperatures are hard for inclusion in the Mediterranean climate
schema. Inland from these areas there are isolated pockets where the climate is borderline
subtropical but these zones are usually classed as oceanic or humid continental. Average summer
temperatures in areas of Europe with this climate are generally not as hot as most other
subtropical zones around the world, but the growing season can be adequately long. Therefore
the winters are too cold to be considered mediterranean or oceanic.
In the central valleys of Catalonia, the Garonne Valley and Rhone Valley in France, the Po
valley in northern Italy, parts of Epirus in Greece around the area of Ioannina, most
of the Vardar Valley in the Republic of Macedonia, parts of extreme northern coasts of Croatia,
Slovenia and Central Serbia fall into this classification. Along the Black Sea coast
of Bulgaria, Romania, Sochi, Russia and southernmost Ukraine have summers too warm to qualify as
oceanic, no freezing month, and enough summer precipitation and sometimes humid conditions
to preclude their classification as Mediterranean but rather border on or are sometimes defined
as Humid continental climates. All these areas are subject to occasional, in some cases repeated
snowfalls and freezes during winter. In the Azores, some islands have this climate, with
very mild and rainy winters and no snowfall, hot summers but with no dry season during
the warmest period, which means that they can be classified neither as oceanic, nor
as Mediterranean, but only as humid subtropical climate, as with Corvo Island.
In many other climate classification systems outside of the Köppen, most of these locations
would not be included in the humid subtropical grouping. The higher precipitation and high
humidity of summers is not present nearly to the degree that it is in subtropical regions
of North America and Asia, making its distinction in Europe all the more difficult.
See also Subtropics
Subtropical ridge Köppen climate classification
References