Geography
In The
News™
Neal G.
Lineback
DROUGHT IN
BRAZIL'S RAIN
FOREST
A strange phenomenon is occurring
in Brazil's normally lush Amazon Basin.
An extended drought has invaded the
region, leaving residents struggling
with the lack of water to replenish
streams and grow crops. Not in historical memory has there been such a severe
drought in Brazil's rain forest region.
Most of the Amazon River's drainage
basin lies within the climates known as
the tropical wet and tropical monsoon.
These two climates have very humid
conditions conducive to heavy vegetation, but there is a distinctive difference
in the vegetative response to the two
climates because the tropical monsoon
climate has a dry season.
Within tropical wet climates around
the world, precipitation normally falls
every month and annual totals may
exceed 100 inches (2.54 m). Some
months may be slightly drier than
others, but seldom is there more than a
month without some rainfall. Most
precipitation occurs as afternoon and
evening thunderstorms, known scientifically as convectional storms. The
humid tropics create perfect conditions
year-round for convectional stormsidentical to summer thunderstorms in
the middle latitudes.
southern Brazil, parts of coastal West
Africa, the west coasts of India, Burma
and Thailand and in a few other places
within the tropics. Most tropical
monsoon climates occur in coastal
locations where seasonal winds-usually
in the summer-bring warm moist air
onshore. The resulting storms caused by
air pushing up over the higher shoreline
are called orographic storms and they
produce copious amounts of precipitation over the wet period.
The natural vegetative response to the
tropical wet climate's year-round
precipitation is a true rain forest, where
the tall trees with a thick canopy shade
the ground. Consequently, there are
little or no lower stories of vegetation in
this broadleaf, evergreen tropical forest
because sunlight does not penetrate the
canopy.
The natural vegetative response to the
seasonal differences in precipitation in
the monsoon climate, however, is a
monsoon forest. The trees in the
monsoon forest are similar to those in
the tropical rain forest, but the seasonal
dry period stresses the trees' foliage. The
result is that the trees lose some of their
leaves, allowing sunlight to reach the
forest floor. Therefore, in the perfect
monsoon forest, lower stories of plants
thrive on the forest floor, often creating a
near-impenetrable understory.
Consequently, tropical forests may
differ considerably from location to
location. Although geographers and
others draw lines around climates and
vegetation regimes, this cartographic
technique is used to help study spatial
patterns, rather than to perfectly delineate boundaries. Most such boundaries
are really transition zones where defin-
ing criteria may comingle. Such is the
case with the vegetative responses to the
tropical wet and tropical monsoon
climates.
The 2005 drought in the Amazonian
tropical rain forest is not only very
unusual, but it injects a stress variable
on the vegetation considerably beyond
normal. The result has been heavy leaf
fall, allowing sunlight to the forest floor
in amounts never before witnessed. The
effects will likely result in plant life
flourishing at lower stories, similar to
that of the monsoon forest, perhaps
radically changing the ecology of the
world's largest rain forest.
Not only is natural vegetation being
stressed, but the drought "...has evaporated whole lagoons and kindled forest
fires, killed off fish and crops, stranded
boats and the villagers who travel by
them (and) brought disease and
wreaked economic havoc" (New York
Times, Dec. 11, 2005).
Daniel C Nepstad, a senior scientist at
the Woods Hold Research Center in
Massachusetts and the Amazon
Institute of Ecological Research in
Belém, Brazil, described the drought
event in the Amazon Basin as "...a kind
of a canary-in-a-coal-mine situation," for
the Times article.
Is this extreme event related to global
warming
issues?
Circumstantial
evidence suggests that it is.
And that is Geography in the News™.
February 10, 2006. #819.
Sources: New York Times, Dec. 11,
2005.
(The author is a Professor Emeritus of
Geography at Appalachian State University, Boone, NC.)
Tropical Rainforests
Tropical wet climates occur in three
general places around the world-the
Amazon Basin of South America, the
Congo Basin in Central Africa and in the
East Indies and Philippines.
Although tropical monsoon climates
may actually have even higher annual
precipitation totals than tropical wet
climates, they have distinct dry seasons.
These dry seasons may range from a
month to six or seven months, when
little if any precipitation falls.
Tropical monsoon climates occur in
parts of Central America around the
mouth of the Amazon and in coastal
©2006
Tropical Wet and
Monsoon Climates
Source: Goode's World Atlas
Geography in the News 2/10/06
C. Knoll
©2006 Maps.com