Answer to Question 1
ANSWER: The southern desert region of North America is dry because it is dominated by the subtropical high most of the year, and cyclonic winter storm systems tend to weaken before they move into the area. The northern region is in the rain shadow of the Sierra Nevada. These regions are deficient in precipitation all year long, with many stations receiving less than 13 cm (5 in.) of rain annually.
Answer to Question 2
ANSWER: Arid climates (BW) occupy about 12 percent of the worlds land area. This climatic type is found along the west coast of South America and Africa and over much of the interior of Australia. Also, a swath of arid climate extends from northwest Africa all the way into central Asia. In North America, the arid climate extends from northern Mexico into the southern interior of the United States and northward along the leeward slopes of the Sierra Nevada. This region includes both the Sonoran and Mojave deserts and the Great Basin.
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