Saturday, March 11, 2017

Tropical Climatic Zones (integrated)

Climate Classification
The variations in interactions between planet earth and the spheres (atmosphere, biosphere, hydrosphere, geosphere) give each location certain distinct climatic characteristics. In order to conveniently analyse them, there is a need to classify them. This would simplify all the climatic types into a few groups, each with their own unique climatic character. 

➽ General Characteristics
➽ The Köppen climate classification scheme divides climates into five main climate groups: A (tropical), B (dry), C (temperate), D (continental), and E (polar). The second letter indicates the seasonal precipitation type, while the third letter indicates the level of heat.

➽ Group A: Tropical (megathermal) climates
This type of climate has every month of the year with an average temperature of 18 °C (64.4 °F) or higher, with significant precipitation.
  • Af = Tropical rainforest climate; average precipitation of at least 60 mm (2.4 in) in every month.
  • Am = Tropical monsoon climate; driest month (which nearly always occurs at or soon after the "winter" solstice for that side of the equator) with precipitation less than 60 mm (2.4 in), but more than 4% the total annual precipitation.
  • Aw or As = Tropical wet and dry or savanna climate; with the driest month having precipitation less than 60 mm (2.4 in) and less than 4% of the total annual precipitation.
➽ Group B: Dry (arid and semiarid) climates
This type of climate is defined by little precipitation.
Multiply the average annual temperature in Celsius by 20, then add
(a) 280 if 70% or more of the total precipitation is in the spring and summer months (April–September in the Northern Hemisphere, or October–March in the Southern), or
(b) 140 if 30%–70% of the total precipitation is received during the spring and summer, or
(c) 0 if less than 30% of the total precipitation is so received.
If the annual precipitation is less than 50% of this threshold, the classification is BW (arid: desert climate); if it is in the range of 50%–100% of the threshold, the classification is BS (semi-arid: steppe climate).
A third letter can be included to indicate temperature. Originally, h signified low-latitude climate (average annual temperature above 18 °C (64.4 °F)) while k signified middle-latitude climate (average annual temperature below 18 °C), but the more common practice today, especially in the United States, is to use h to mean the coldest month has an average temperature above 0 °C (32 °F), with k denoting that at least one month's averages below 0 °C.
  • BWh = Hot desert climate
  • BWk = Cold desert climate
  • BWn = Mild desert climate
  • BSh = Hot semi-arid climate
  • BSk = Cold semi-arid climate
  • BSn = Mild semi-arid climate

➽ Specific Characteristics

➽ Group A: Tropical/megathermal climates

Tropical climates are characterized by constant high temperatures (at sea level and low elevations); all 12 months of the year have average temperatures of 18 °C (64.4 °F) or higher.
➽ Af: Tropical rainforest climate[edit]
Main article: Tropical rainforest climate
➾ All 12 months have average precipitation of at least 60 mm (2.4 in). These climates usually occur within 10° latitude of the equator. This climate is dominated by the doldrums low-pressure system all year round, so has no natural seasons in terms of thermal and moisture changes.
Some of the places with this climate are indeed uniformly and monotonously wet throughout the year (e.g., the northwest Pacific coast of South and Central America, from Ecuador to Costa Rica; see, for instance, Andagoya, Colombia), but in many cases, the period of higher sun and longer days is distinctly wettest (as at Palembang, Indonesia) or the time of lower sun and shorter days may have more rain (as at Sitiawan, Malaysia).
➽ Am: Tropical monsoon climate[edit]
Main article: Tropical monsoon climate
➾ This type of climate, most common in South Asia, results from the monsoon winds which change direction according to the seasons. This climate has a driest month (which nearly always occurs at or soon after the "winter" solstice for that side of the equator) with rainfall less than 60 mm, but more than 1/25 the total annual precipitation.[8]:208

➽ Aw: Tropical wet and dry or savanna climate[edit]

Main article: Tropical savanna climate
➾ Aw climates have a pronounced dry season, with the driest month having precipitation less than 60 mm and less than 1/25 of the total annual precipitation.:208–11[8]
Most places that have this climate are found at the outer margins of the tropical zone from the low teens to the mid-20s latitudes, but occasionally an inner-tropical location (e.g., San Marcos, Antioquia, Colombia) also qualifies. Actually, the Caribbean coast, eastward from the Gulf of Urabá on the Colombia–Panamá border to the Orinoco River delta, on the Atlantic Ocean (about 4,000 km), have long dry periods (the extreme is the BSh climate (see below), characterised by very low, unreliable precipitation, present, for instance, in extensive areas in the Guajira, and Coro, western Venezuela, the northernmost peninsulas in South America, which receive <300 mm total annual precipitation, practically all in two or three months).
This condition extends to the Lesser Antilles and Greater Antilles forming the circum-Caribbean dry belt. The length and severity of the dry season diminishes inland (southward); at the latitude of the Amazon River—which flows eastward, just south of the equatorial line—the climate is Af. East from the Andes, between the dry, arid Caribbean and the ever-wet Amazon are the Orinoco River's llanos or savannas, from where this climate takes its name.

➽ Group B: Dry (arid and semiarid) climates

Main articles: Desert climate and Semi-arid climate
➾ These climates are characterized by actual precipitation less than a threshold value set equal to the potential evapotranspiration.[8]:212The threshold value (in millimeters) is determined as:
Multiply the average annual temperature in °C by 20, then add (a) 280 if 70% or more of the total precipitation is in the high-sun half of the year (April through September in the Northern Hemisphere, or October through March in the Southern), or (b) 140 if 30%–70% of the total precipitation is received during the applicable period, or (c) 0 if less than 30% of the total precipitation is so received.

➾ According to the modified Köppen classification system used by modern climatologists, total precipitation in the warmest six months of the year is taken as reference instead of the total precipitation in the high-sun half of the year.[10]


➾ If the annual precipitation is less than 50% of this threshold, the classification is BW (arid: desert climate); if it is in the range of 50%–100% of the threshold, the classification is BS (semi-arid: steppe climate).
A third letter can be included to indicate temperature. Originally, h signified low-latitude climate (average annual temperature above 18 °C) while k signified middle-latitude climate (average annual temperature below 18 °C), but the more common practice today, especially in the United States, is to use h to mean the coldest month has an average temperature above 0 °C (32 °F), with k denoting that at least one month averages below 0 °C.
Desert areas situated along the west coasts of continents at tropical or near-tropical locations are characterized by cooler temperatures than encountered elsewhere at comparable latitudes (due to the nearby presence of cold ocean currents) and frequent fog and low clouds, despite the fact that these places rank among the driest on earth in terms of actual precipitation received. This climate is sometimes labelled BWn. The BSn category can be found in foggy coastal steppes.
On occasion, a fourth letter is added to indicate if either the winter or summer half of the year is "wetter" than the other half. To qualify, the wettest month must have at least 60 mm (2.4 in) of average precipitation if all 12 months are above 18 °C (64 °F), or 30 mm (1.2 in) if not; plus at least 70% of the total precipitation must be in the same half of the year as the wettest month — but the letter used indicates when the 'dry' season occurs, not the 'wet' one. This would result in Khartoum, Sudan, being reckoned as BWhw; Niamey, Niger, as BShw; Alexandria, Egypt, as BWhs; Asbi'ah, Libya, as BShs; Ömnögovi Province, Mongolia, as BWkw; and Xining, Qinghai, China, as BSkw (BWks and BSks do not exist if 0 °C in the coldest month is recognized as the h/k boundary.[citation needed]) If the standards for neither w nor s are met, no fourth letter is added.


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