Definitions

Subtropical climate

Humid subtropical climate

Humid subtropical climate (Köppen Cfa or Cwa) is a climate zone characterized by hot, humid summers and chilly to mild winters. This climate type covers a broad category of climates, and the term "subtropical" may be a misnomer for the winter climate in the cooler areas within this category; in fact Wladimir Köppen never talked about a humid subtropical climate, but rather about a sinic climate (sinisches Klima), for his subclass Cw of temperate climates. Significant amounts of precipitation occur in all seasons in most areas. Winter rainfall (and sometimes snowfall) is associated with large storms that the westerlies steer from west to east. Most summer rainfall occurs during thunderstorms and an occasional tropical storm, hurricane or cyclone.

Humid subtropical climates lie on the southeast side of all continents except Antarctica, roughly between latitudes 25° and 40° north and south. One of the only exceptions where this climate zone reaches up to latitude 46° North, are in the Po Valley and the Toulouse regions in Europe.

The definition of this climate is for the coldest month mean temperature to be between -3°C and 18°C, and the warmest month to be above 22°C.; and either a dry winter with less than one tenth of the precipitation of the wettest summer month (Köppen: w) or without dry season (Köppen: f, winter months get more than one tenth of the precipitation of the wettest summer month and summer months get at least 40mm per month or more than one third as much the wettest winter month).

Africa

In Africa this climate is only found in a relatively small area on the South East

The climate of this region is characterised by oceanic influences that give mild temperatures especially in winter when temperatures do not drop as low as in many other regions within the humid subtropical category. For example Richards Bay experiences a daily average minumum of 12 °C and a daily average maximum of 23 °C in the coldest month and did not drop below 4 °C in the 30 years of records from 1961. Rainfall is distributed throughout the year but is heavier in summer with a high of 172 mm for January and a low of 57 mm for June at Richards Bay.

Asia

Humid subtropical climates in Asia differ from those in other continents in generally having a very pronounced dry winter even on the poleward boundary of this region. They occupy extensive arcs of relatively low land from northern Pakistan circling the Himalayas to China, Southern Coast of South Korea and Japan (most part of Honshu, Kyūshū and Shikoku). Some major Asian cities in this climate zone include Kathmandu, Chongqing, Chengdu, Shanghai, Nanjing, Busan, Kyoto and Tokyo. Hong Kong and Taipei are on the equatorward boundary of this zone.

In most of this region, there is very little precipiation during the winter owing to the powerful anticyclonic winds from Siberia. Only in those parts of coast eastern China between about the Yellow River and the Pearl River is there sufficient winter rainfall to produce a Cfa climate and even in these areas rainfall and streamflow show a very pronounced summer peak quite unlike other regions of this climate type. The only area where the winter rainfall equals the summer rain is on the "San-in" (Sea of Japan) coast of Japan, which during winter is effectively on the windward side of the westerlies. The winter rainfall 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 mm (40 inches), and in areas below the Himalayas can be much higher still. In the west humid subtropical climate border on continental climates as altitude increases, or on winter-rainfall climates in Pakistan.

Isolated humid zones in western Asia

Although humid climates in Asia are mostly confined to the southeastern quarter of the continent, there are some isolated areas on the Black and Caspian Seas than possess humid climates that are unusually warm for their high latitudes.

In the narrow Caspian coastal strip of Iran (Gilan and Mazandaran) a humid subtropical climate prevails at an unusually high latitude. Annual rainfall ranges from around 740 mm (29 inches) at Sari to over 2,000 mm (78 inches) 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 (16 inches). Temperatures are generally moderate in comparison with other parts of western Asia. In Rasht, the average maximum in July is around 28 °C (82 °F) but with near-saturation humidity, whilst in January it is around 9 °C (48 °F).

In Georgia and the adjacent region of Turkey, the Kolkheti Lowland has a climate similar to that of Gilan in Iran. 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 it falls throughout the year. This climate is almost a Cfa/Cfb borderline case, however.

North America

In North America, humid subtropical climates are almost exclusively the domain of the American South, the eastern half of Texas (includes South Texas), Louisiana, most of Arkansas, Mississippi, Tennessee, Kentucky, Alabama, North Carolina, South Carolina, Georgia, most of Florida and Virginia, excluding upland regions of the Appalachians. It also exists in low lying or urban areas including Delaware, southwestern West Virginia, eastern and southern Maryland, southern Pennsylvania, most of New Jersey, parts of Connecticut, southern Missouri, and southern Ohio. The most classic example of a humid subtropical climate is the deep south, because the summers are long and almost tropical, and it only reaches freezing a few times in the winter with rare snowfall. Summer conditions in this zone are hot and humid, with daily averages ranging between 25°C (77°F) and 30°C (86°F). Major cities in this climate zone include: Houston, Dallas, Atlanta, Memphis, Birmingham, New Orleans, Louisville, Nashville, Charlotte, Jacksonville, Orlando, Tampa, Richmond, Norfolk, and Little Rock. Cities on the northern periphery of this zone include: Tulsa, St. Louis, Cincinnati, Washington D.C., Baltimore, and Philadelphia. The climates of Dallas and Oklahoma City display a marked reduction in rainfall that suggests a shading into steppe climates to be found farther west, as in Lubbock, Texas. There is some debate over whether New York City falls under this category although it is usually described as cfa (humid subtropical).

Characteristics and variants

The southernmost limits of this climate are around Miami and southern coastal Texas, and areas further south have a true tropical climate with very warm weather year round and minimal temperature differences between seasons. By contrast, the northernmost limits of the humid subtropical region experience much greater seasonal variation. They draw influence from the Atlantic Ocean and its bays, Delaware Bay and Chesapeake Bay including Washington D.C.. Further away from the Atlantic, it is found at the edge of the Blue Ridge Mountains west to Louisville, Kentucky, then roughly along the lower Ohio River through Paducah, Kentucky to a line south of Springfield, Missouri, that does not include the city itself. Areas further north than this, inland, or at a higher elevation fall into the humid continental climate category with harsher winters. Snowfall varies greatly in this climate zone. In areas around Florida and the Gulf Coast, snowfall is very rare and it occurs at most a few times per generation. In inland southern cities farther north, such as Atlanta, Memphis, Little Rock, Nashville, Dallas, Greenville, Charlotte, Raleigh, and Norfolk, snowfall does happen, occasional snow and ice storms are not unusual, however most of the winter temperatures remain above or well above freezing with hardy plant growth. In the northern limits of this climate zone, however, cities such as Louisville, Cincinnati and Philadelphia, experience snow every winter, sometimes accumulating heavily although it melts more quickly than in regions to the north. Precipitation is plentiful in the humid subtropical climate zone. Although most areas tend to have precipitation spread evenly throughout the year, a somewhat monsoon-like pattern is seen in parts of the Southeast (in locales such as Augusta, Georgia and Columbia, South Carolina), which experience dry winters (by humid subtropical standards) and warm spring, followed immediately by a long, hot, rainy and humid summer. In addition, areas in Texas that are slightly inland from the Gulf of Mexico, such as Austin, generally see a peak of precipitation in the spring, and a deep, drought-like nadir in mid-summer.

Australia

The humid subtropical climate dominates most of eastern Australia south from about Bundaberg, Queensland down to about Bega on the south coast of New South Wales. It extends from the coast inland to about Dubbo and the Warrumbungle and Nandewar mountain ranges, where it grades into arid climates. In the Great Dividing Range and to the south of about Bega, this climate type grades into warm temperate climates (Köppen Cfb) as at Guyra and Katoomba, in New South Wales.

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.

Many of Australia's major cities are also in this climate zone, including Sydney, Brisbane, Gold Coast-Tweed Heads, Newcastle and Wollongong.

Variations in Australia

There is considerable variation in climate within this zone. Annual rainfall on the coast can reach as high as 2,000 mm (80 inches) in favourable locations and is generally above 1,000 mm (40 inches). 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 (22 inches) in 1915 to more than 2,780 mm (110 inches) in 1950. There is usually a distinct summer rainfall maximum that becomes more pronounced moving northwards: in Brisbane the wettest month (February) receives five times the rainfall of the driest (September) very warm but not excessive: the average maximum in January is usually around 28 °C (82 °F) and in July around 19 °C (66 °F). Frosts are extremely rare except at higher elevations.

In the Darling Downs and further south, the summer rainfall maximum is less marked and by the time one reaches Dubbo, there are actually on average more rainy days in the winter months. Temperatures here are more extreme, with summers being generally very hot with maxima of around 32 °C (90 °F) and frosts being common during dry winters: at Mitchell the temperature has reached as low as -9.4 °C (15 °F).

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

Some areas of Europe, such as parts of southern France, northern Italy (Po River Valley), and coastal Croatia have summers too warm (>22°C in the warmest month) to qualify as oceanic, no freezing month, and enough summer precipitation to preclude their classification as Mediterranean. This is a narrow band of climate that could be classified as humid sub-tropical, which includes some densely-populated territory.

Examples

References

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