Desert Zone of the Temperate Belt

Desert Zone of the Temperate Belt

 

a natural zone in the temperate belt of the northern hemisphere in which the predominant landscapes are deserts. In Eurasia the zone stretches from the shores of the Caspian Sea in the west to the Ordos Plateau in the east and has a maximum width of 700-800 km. In North America the deserts of the temperate belt occur in patches in the broad intermontane basins of the Great Basin highlands, where their existence is the result of topographic features. The Cascade Range acts as a barrier that intercepts much of the precipitation carried by the prevailing westerly winds. Deserts do not occur in the temperate belt of the southern hemisphere.

Much of the zone is covered by sandy deserts—the northern Kyzylkum, the Muiunkum, the Sary-Ishikotrau, the Greater and Lesser Barsuki, the Aral Karakum, the North Caspian Desert, and the Dzungarian and Kashgar plains. There are also other types of deserts: a cobble gypsum desert on the Ustiurt Plateau between the Caspian and Aral seas, a clay desert on the Turgai Plateau, and the clay and stone Betpak-Dala Desert to the west of Lake Balkhash. The temperate deserts do not form a continuous expanse in Eurasia but are broken up by the Tien-Shan and Dzungarian Alatau mountain systems.

The climate of the desert zone of the temperate belt is continental. Summers are hot, with mean July temperatures of 22°-32°C, rising to a maximum of 50°C. Winters are cold, with mean January temperatures ranging from –7° to – 15°C; the minimum is –42°C. The annual precipitation averages 100-200 mm, although in places it is less than 50 mm. Most of the precipitation occurs in summer in Eurasia and in winter in North America. Evaporation is seven to ten times greater than the annual precipitation. The surface of the desert zone of the temperate belt receives 500-630 kilojoules per sq cm (120-150 kilocalories per sq cm) of solar radiation each year.

Surface runoff is poorly developed. Intermittent streams predominate, and the only perennial rivers are through-flowing rivers. The groundwater is usually saline, although fresh groundwater occurs under barchans. Most of the lakes have no outlets and are brackish or saline; their size, outline, and level may vary greatly in different years. The deficiency of soil moisture is most apparent in the summer and autumn. The soils are gray-brown, low in humus, and strongly carbonate; the Ustiurt Plateau has gypsum soils. Sandy desert soils occur widely, and solonchaks are common in low-lying areas.

The vegetation has adapted to a long dry growing season, cold winters, and extremely saline soils. In sandy areas grow shrub and tree formations with black and white Haloxylon species, sand acacia, and species of Ephedra. The loess soils of the piedmont plains support wormwood (Artemisia) and ephemerals. Wormwood also occurs on loamy soils, and halophilic shrubs are found on gypsum cobble soils. In the North American desert the vegetation is sparse and consists primarily of shrubs with a large number of succulents (cacti). The vegetation of this desert zone is widely used for grazing livestock throughout the year.

The animal world of the temperate desert zone consists of a comparatively small number of species owing to the harsh ecological conditions, particularly the low air and soil temperatures in winter. The most common mammals are rodents, including gerbils, jerboas, and ground squirrels. The most prevalent ungulates are the goitered gazelle and saiga, and the main predators are wolves and foxes. There are many turtles, lizards, and snakes.

M. P. PETROV

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