Download tropical wet and dry climate

Chapter 15
Earth’s Climates
Climate refers to the statistical properties of the atmosphere
and is concerned with the long-term behavior,
or expected (typical) conditions.
The most widely used climatic classification scheme is
the Koeppen system based on world distribution
of natural vegetation boundaries and the
combinations of monthly mean temperature
and precipitation associated with those boundaries.
Climate types according to Koeppen.
World map of Koeppen climates.
The Tropical Climates consist of three groups,
each of which is warm year-round.
The tropical wet climate has significant rainfall
every month of the year,
the tropical wet and dry climate has a
pronounced dry season,
and the monsoonal climate undergoes
relative dryness for 1 to 3 months but receives
sufficient moisture that vegetation need not be
adapted to seasonal drought.
Tropical Wet (Af) climates have no dry period and precipitation is almost
always convectional with strong solar heating of the surface triggering
brief but heavy thundershowers in the mid to late afternoon.
Monsoonal (Am) climates usually occur along tropical, coastal areas
subjected to predominant onshore winds that supply warm, moist air
to the region throughout most of the year.
Tropical Wet and Dry (Aw) often occur along the poleward margins of
the Tropics and border dry climates on one side and tropical wet climates
on the other. They undergo much greater seasonality in precipitation and
temperature than do the tropical wet and the monsoonal climates.
Tropical wet and dry climates are associated with the savanna.
This vegetation consists mainly of grasses interspersed with
widely separated trees or clumps of trees.
The lack of forest results from numerous factors,
including recurrent fire, waterlogged soils, and the
development of hard layers within the soil.
The Dry Climates of the world can be divided by the
level of aridity and by their latitudinal position.
Semi-deserts are transitional zones that separate the
true deserts from adjacent climates. They are also
called steppe climates, with reference to the
associated vegetation type consisting of short grasses.
True deserts are so dry that only sparse vegetation
consisting entirely of xerophytic species can take hold.
Subtropical Deserts (BWh) tend to exist in the subtropical regions,
particularly within the western portions of the continents as a result
of subsidence associated with the Hadley circulation.
Subtropical Steppe (BSh) are marked by aridity, high year-to-year
variations in precipitation, extreme summer temperatures, large annual and
daily temperature ranges, and commonly border the subtropical deserts.
Mid-latitude Deserts (BWk) result from extreme continentality in
regions deep within continental interiors or downwind of orographic
barriers that cut off the supply of moisture from the ocean.
Mid-latitude Steppe (BSk) accounts for most of the arid regions of
western North America and has the same temperature characteristics
as the mid-latitude deserts. The primary difference between the two
is the greater amount of precipitation in the steppes.
The Mild Mid-latitude climates are located in parts of the
latitude range between 30° and 60° in either hemisphere.
The term mild refers to the winter temperatures and
not necessarily those of the summer.
Mediterranean climates can be found along the
west coasts between about 25° and 40° latitude.
At about the same range of latitude on the eastern
side of continents are the humid subtropical climates.
The marine west coast climates lie adjacent to
and poleward of the mediterranean climates.
Mediterranean (Csa, Csb) climates are the only ones that have a distinct
summer dry season and a concentration of precipitation in the winter.
Annual precipitation increases with latitude and with elevation
along windward slopes in mediterranean climates.
Humid subtropical (Cfa, Cwa) climates lie within the lower middle latitudes
of eastern North America, South America, and Asia. They have a distinct
tropical feel during their long summers and receive abundant precipitation.
Marine West Coast (Cfb, Cfc) climates normally occur poleward of
mediterranean climates. Both summers and winters are typically mild
with low annual temperature ranges and a wide range of precipitation.
The Severe Mid-latitude climate group includes two climates,
humid continental and subarctic, both of which are marked by
very cold winters. These climates require large continental areas
within the high-middle latitudes between about 40° and 70°.
Both of the severe mid-latitude climates receive precipitation
throughout the year and have no true dry season.
Humid Continental (Dfa, Dfb, Dwa, Dwb) climates are found between
40° N and 55° N in the eastern parts of continents with warm and often
hot summers followed by cold winters. The coniferous forest found here
is referred to as the boreal forest in North America and the taiga in Asia.
Subarctic (Dfc, Dfd, Dwc, Dwd) climates occupy the northernmost extent
of the severe mid-latitude regions. Summer temperatures are lower
than humid continental regions and winter mean monthly temperatures
can be extremely low. Precipitation is greater in the summer than winter.
Polar Climates exist in the highest latitudes poleward of about
70° at the high latitude boundaries of the subarctic climates.
The most equatorward and milder of the two
is the tundra. At the most poleward regions of the
globe lie the true ice cap climates.
Tundra (ET) climates are named for the associated vegetation type that
consists primarily of low-growing mosses, lichens, and flowering plants,
with a few woody shrubs and trees. Winters are severe with a
perennially frozen layer below the surface called permafrost.
Polar Ice Cap (EF) areas exist where ice covers the ground the entire year.
The mean temperature of the warmest month does not rise above 0 °C.
Most areas of ice cap receive little precipitation because of the intense cold.
Highland Climates (H) are governed by topography
and found in large mountain or plateau areas.
This group contains an extremely rich collection of climates.
In high mountains there can be large changes in
mean temperature over short distances while
mountain slopes can enhance precipitation on their windward
sides and simultaneously create a rainshadow downwind.
The next chapter examines
climate changes: past and future.