Geoscience Reference
In-Depth Information
current structure and appearance of the rainforest may be very different from the
rainforests of the past.
Climate
The key to the lush vegetation and high species diversity in the Tropical Rainforest
Biome is the climate. Tropical rainforests experience warm temperatures through-
out the year, averaging 79
C). Average annual precipitation is
between 100-180 in (2,500-4,500 mm). Tropical areas closer to the tropical mar-
gins experience a decreased annual rainfall, with the exception of those areas sub-
ject to intense monsoonal activity such as in Southeast Asia. Individual areas on
the west side of continents, such as Cameroon in Africa, and between Panama and
Ecuador in South America, have recorded even higher rainfall, as much as 475 in
(12,000 mm) at Mount Cameroon, and 400 in (10,000 mm) in Colombia.
As mentioned in Chapter 1, several major wind and climatic systems influence
the Tropical Rainforest Biome. These include the Northeast and Southeast Trade
Winds, the Intertropical Convergence Zone (ITCZ), tropical cyclones, and mon-
soons. Local convective precipitation contributes to rainfall totals within the rain-
forest. In the equatorial tropics, the high water content of air, in combination with
the convergence of unstable airmasses, produces intensive vertical movement of
moist air through convection. These are the areas of the world with the highest
amounts of rainfall. The core regions are the Amazon Basin, the Congo Basin, and
the Indomalayan archipelago.
Tropical cyclones also produce substantial rainfall in the tropics. These storms,
in combination with summer monsoonal rains, are sufficient for the existence of
rainforests away from the equatorial zone. Tropical cyclones, called typhoons in
the Pacific and Indian Ocean influence vegetation on the eastern and southern
parts of Asia, northeastern Australia, and Madagascar. Atlantic cyclones, called
hurricanes in the Northern Hemisphere, primarily affect the Caribbean and Central
American forests.
The climate of tropical rainforests is classified as a tropical moist climate, or Af
using Koeppen's climate classification, where temperatures remain high and pre-
cipitation averages greater than 2.4 in (60 mm) per month (see Figure 2.4). Rainfor-
ests are located in and typically limited to the areas where precipitation is higher
than evaporation, leading to a surplus of water. This creates a positive water bal-
ance. Tropical rainforests can extend beyond these areas when groundwater reser-
voirs are sufficient to overcome occasional drought events.
Taking a macroclimatic or large-scale view of this tropical biome, climate and
weather play an important role in the distribution and physiology of vegetation
and the internal forest cycles within these regions. Climate and weather are deter-
mined by incoming solar radiation (insolation), absorption, and reradiation (return
of energy to the atmosphere) from the Earth's surface. Global atmospheric circula-
tion and hydrologic cycles are also important components.
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