Geoscience Reference
In-Depth Information
more influential. Interior rainforests typically experience convective precipitation
that is caused by warm, humid air (from evaporation processes within the forest) at
the surface rapidly rising, cooling aloft. Similarly, as air rises up mountains it cools
and the water vapor in the air condenses. Since cool air can hold less water, when
the airmass becomes saturated rain falls. This typically happens in the late after-
noon and can bring torrential rains into and through the night. Hurricanes, cyclo-
nes, or typhoons are low-pressure systems that develop in warm tropical waters.
They build up speed and momentum at sea and when they reach land rainfall can
be extremely intense. The accompanying strong winds can cause widespread flood-
ing and destruction. Tropical cyclones are concentrated in the Pacific and Indian
oceans affecting Madagascar, Southeast Asia, and Australia. Atlantic cyclones
occur in the Caribbean and Central America.
The El Ni
no-Southern Oscillation (ENSO) is a cyclical, global ocean-atmos-
pheric phenomenon that affects the tropical regions of the world. El Ni
~
no and its
~
counterpart La Ni
na influence temperature changes in the surface waters of the
tropical Pacific Ocean, with a significant effect on the weather patterns, especially
in the Southern Hemisphere. During an El Ni
~
no event, the warm waters of the cen-
tral equatorial Pacific are pushed eastward to the normally cold water coasts of
South America. This warm water with accompanying warm air above provides
abundant moisture to some areas that are typically dry. In contrast, the easterly
movement of warm water leaves the western Pacific without its normally abundant
moisture. El Nino causes weather patterns that can produce excessive rain in some
places and extreme drought in others. It has been linked to flooding in the tropical
dry forests along the Pacific Coast of Central and South America and destructive
drought and fires in the tropical forests of Asia and Australia. Tropical forests in
Asia experience extreme drought during severe El Ni
~
no events, leaving them vul-
nerable to destructive fires that destroy entire forest stands. Global climate change
is thought to have increased the frequency of El Ni
~
no events; however, research is
ongoing to assess the true impacts of global warming on El Ni
~
no, as well as other
~
climatic phenomenon.
Soils
Soils within the tropical zone are the product of high heat and moisture over mil-
lions of years. They are primarily highly weathered ancient soils with high acidity
and low nutrient and organic matter content. They tend to be red or yellow in
color. Other younger soils do occur within the tropics, and they tend to be more fer-
tile and have a higher nutrient and mineral content than those developed on an-
cient surfaces. They are brown or black in color due to the higher levels of organic
matter in the soil and their volcanic origins. Soil types are discussed in later
chapters.
