Geoscience Reference
In-Depth Information
D I S C O V E R . . .
THE ATACAMA dESERT
The driest place on Earth is the Atacama Desert on the west
coast of South America. This region is on the northern mar-
gin of the cold midlatitude desert climate ( BWk ) and extends
about 1000 km (600 mi) from the southern border of Peru into
northern Chile. To give you an idea of the Atacama's extreme
aridity, consider that some areas within the desert have never
received any measurable precipitation in recorded history.
Several interrelated factors explain the aridity of the Ataca-
ma Desert. The region lies on the west side of the Andes Moun-
tains, which are a major orographic barrier to moisture-laden
easterlies that circulate across tropical South America. Thus,
the Atacama Desert lies in the rain shadow of the Andes, where
descending air under high pressure compresses and warms so
much that precipitation is rare. In addition, the region borders
the Humboldt Current (also called the Peru Current). As a re-
sult, the air above the current is very stable with little convec-
tion. Given these combined factors, the Atacama Desert looks
otherworldly. It seems so alien, in fact, that it has been used to
simulate the Martian landscape in science fiction movies.
BRAZIL
PERU
BOLIVIA
BOLIVIA
BO
PACIFIC
OCEAN
CHILLLE
CHILE
ARGENTINA
A typical scene in the Atacama Desert. Note the very sparse vegetation
in this extremely dry climate.
This map shows the geographic relationship of the Atac-
ama Desert, Humboldt Current, and Andes Mountains.
temperature range than the BWh climate and slightly
more precipitation. This greater precipitation occurs
because periodic midlatitude circulatory systems move
through the region in winter. Vegetation is sparse, con-
sisting of some grasses, cactus, and isolated trees.
KEY CONCEPTS TO REMEMBER ABOUT
THE dRY ARId ANd SEMI-ARId
( B ) CLIMATES
1.
Four major dry arid and semi-arid climates are recognized:
( a ) hot low-latitude desert climate ( BWh ); (b) hot low-lati-
tude steppe climate ( BSh ); (c) cold midlatitude steppe cli-
mate ( BSk ); and (d) cold midlatitude desert climate ( BWk ).
4.
The cold midlatitude steppe climate ( BSk ) occurs in plac-
es like Denver, Colorado, which lie in the rain shadow of
major mountain ranges. Large temperature ranges and
seasonal precipitation variations occur in these areas.
Vegetation consists largely of short to medium grasses.
2.
The hot low-latitude desert climate ( BWh ) occurs in
places like northern Africa and is dominated largely by
the STH Pressure System. Vegetation is very sparse.
5.
The cold midlatitude desert climate ( BWk ) occurs
in places like the Gobi Desert in north-central China.
These regions are dry because they either lie adjacent
to cold ocean currents (like northern Chile) or are deep
within continents. Vegetation is limited.
3.
The hot low-latitude steppe climate ( BSh ) lies slightly
poleward of the hot low-latitude desert climate ( BWh )
in places like Saudi Arabia and Iraq. It thus has a wider
 
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