Geoscience Reference
In-Depth Information
(a)
(b)
Figure 9.5 Low-latitude desert climates.
(a) Vegetation in the hot low-latitude desert climate (
BWh
) is very sparse due to the drying ef-
fects of subtropical high-pressure cells. (b) Vegetation in the hot low-latitude steppe climate (
BSh
) is very similar to that seen in the Mojave
Desert in the southwestern Unted States. Although the vegetation here is sparse, some trees like this Joshua tree can grow.
deep within the continental interiors of North America and
Eurasia (Figure 9.2) and is most often associated with the rain
shadow effect that occurs in the lee of major mountain ranges,
such as the Rocky and Himalayan Mountains. As discussed in
Chapter 7, this effect occurs because maritime air masses are
effectively blocked by the mountains, allowing relatively dry
continental air masses to dominate the region. Most precipita-
tion falls in summer and is related to convectional processes.
When precipitation does fall in the winter, it is usually asso-
ciated with the midlatitude storm track. Given the relatively
high amount of precipitation in this dry climate, compared to
the desert-like environments examined earlier, vegetation in
this region consists of short-grass prairie (Figure 9.6a). Given
your understanding of continental air masses, it should be no
surprise that the annual temperature range in the dry midlati-
tude climate is large, ranging from hot to quite cold. (
Do you
know why this pattern occurs?
)
The second midlatitude dry climate on Earth is the cold
midlatitude desert climate (
BWk
). This climate zone encom-
passes one of the smallest overall areas of any climate group,
occurring only in central Asia, north-central China, Patagonia
in Argentina, and at high elevations in the southwestern United
States. The primary distinguishing characteristic of this climate
is that it receives 15 cm (5.9 in.) or less of rainfall per year.
The annual monthly maximum temperature range in this zone
can be high, ranging from ~0°C in the winter months to ~30°C
(85°F) in July. The dry character of this climate results in typi-
cal desert vegetation (Figure 9.6b).
(a)
(b)
Figure 9.6 Midlatitude dry climates.
(a) Short-grass prairie in eastern Colorado. This low-growing vegetation is a response to the low
rainfall in this climate region (
BSk
). (b) The Hongoryn Els sand dunes in Mongolia's Gobi Desert. This sparsely vegetated landscape occurs
because of cold/dry conditions in the interior of Asia (
BWk
). This dune field is about 200 km (125 mi) long.
