Geoscience Reference
In-Depth Information
Climate
The climate of the African rainforest is consistently warm and humid with little
seasonal or annual fluctuation. Temperatures average between 70
and 90
F (21
and 32
C) during the day, with cooler temperatures along the coast. Mean
monthly minimum temperatures show little variation, ranging from 57
-63
F
(14
C). Hu-
midity remains at least 70 percent and is often 90-100 percent. The climate inside
the rainforest has a smaller temperature range than outside the forest.
Most African rainforests are drier than those in other regions and have annual
rainfall totals of 60-80 in (1,500-2,500 mm). Rain occurs most months, with no
more than two or three months receiving less than 4 in (100 mm). In certain areas,
rainfall can be extreme; for example, 470 in (12,000 mm) was recorded in the forest
on Mount Cameroon. Although rainfall is abundant, it is the limiting factor in rain-
forest distribution. Tropical rainforests give way to tropical seasonal forests, wood-
lands, and savannas when a distinct dry season brings rainfall of less than 4 in (100
mm) for several months.
Although day length within the African rainforest changes little throughout
the year, cloud cover provides a significant variation in the amount of solar radia-
tion reaching the forest. In the rainiest season, there can be as little as two hours of
sunlight directly reaching the forest. Even in the drier season, the forest remains
misty.
The global circulation that heavily influences the African rainforest is the shift-
ing ITCZ. In Africa, a maritime airmass flowing southwest from the Atlantic
Ocean meets an opposing hot, dry continental airmass from the northeastern
deserts. Where the two meet is a zone of instability and high rainfall. Airmasses
move seasonally from north to south with the shifting ITCZ, varying from 5
-17
C), with maximum temperatures reaching 84
-90
F (29
-32
-7
N
latitude in January to 17
S latitude in July. These movements account for the
seasonal distribution of rainfall in tropical Africa. To the south of this zone is an
area of continuous low clouds, but less precipitation. The Trade Winds are less of a
factor in the African rainforest than in the Neotropics, but they may be important
in the dispersal of species. From December to March, hot dry winds known as the
Harmattan Winds blow from the Sahara Desert, reaching the rainforests of West
Africa. In the Congo Basin, dry winds from the Ethiopian Highlands blow over the
rainforest. This is less severe than the winds encountered in West Africa. Both
winds bring warm dry air and decreased rainfall to the rainforests.
General forecasts about the future African climate in face of global warming
predict increased aridity in equatorial Africa, with climate shifts causing the migra-
tion of vegetation zones and limiting the distribution of tropical rainforest. Slight
temperature variations can cause significant effects on animal composition, which
in turn affect plant pollination and seed dispersal with consequent deleterious
effects on the forest.
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