What are temperate deserts?
Temperate deserts (or cold winter deserts) are geographically defined in different ways. Probably the most famous one is the climate classification after Köppen & Geiger (1961) with its definition BW (desert climate) k (cold in winter). Udvardy (1975) gives a more broad definition, which is the universal basis for the classification of UNESCO world heritage sites. Other commonly used definitions are given for instance by Rachkovskaya et al. (2003), Schröder (1998), Schultz (2002), Shmida (1985) or Walter & Breckle (1999).
All of them agree that temperate deserts are continental deserts, whose aridity is explained by its distance to oceans or their position in the rain shadow of larger mountain ranges. Therefore they are also called continental deserts. They are characterized by a distinct seasonal climate, with strong, long-lasting frost in winter and extremely hot summer, in combination with very low annual precipitation of less than 100 mm. Temperature of the cold winter deserts and semi-deserts fluctuates between -45°C and +50°C. While the temperate deserts of Central Asia have their maximum in precipitation in the winter months, the climate type of temperate deserts in Mongolia has its maximum in precipitation in the summer months.
The majority of deserts in Central Asia spreads over the the lowlands of Kazakhstan, Turkmenistan and Uzbekistan, with its vast deserts Karakum (black sand), Kyzylkum (red sand), Muyunkum, Ustyurt Plateau and Aralkum (bottom of former Aral Sea). The share of deserts of the total countries territory of Turkmenistan and Uzbekistan is between 80-90%. In the Chinese province Xinjiang the desert Taklamakan is located and in Mongolia the desert Gobi. 95% of all temperate deserts are found in Central Asia. Comparably small areas are located in the Great Basin of North America and in parts of Patagonia in South America.
Subdivision of Eurasian temperate deserts
The Eurasian temperate deserts can be subdivided. Therefor, several various concepts exists. One of the most applicable and useful concept is that after Petrov 1965. According to Petrov the Eurasian deserts can be subdivided into four subregions: Iran-Turanian deserts (I), Kazakh–Dzungarian semi-deserts and deserts (II), Central Asian deserts of Mongolia and North-China (III) as well as the high-altitude deserts in Tibet (IV) (see map after Petrov 1965 in Walter 1968). As Iran-Turanian deserts have a significant form, they will be described more precisely below. These deserts are the most species-rich among the Eurasian temperate deserts.
The Kazakh-Dzungarian semi-deserts and deserts (II) are bounded towards the South along the northern part of the Aral Sea as well as the river Syr-Darya and then along with the foothills of the northern Tian Shan comprising the Lake Balkhash with the river Ili. To the North these deserts go over towards the steppes of Kazakhstan, Russia and Mongolia.
In Russian-speaking countries, the Eurasian temperate deserts are usually divided into “northern” and “southern” deserts. Both of them mostly extend across the post-Soviet countries, in particular Kazakhstan, Turkmenistan and Uzbekistan. Generally speaking, the “northern” deserts correspond with Kazakh-Dzungarian semi-deserts and deserts, whereas the “southern” deserts are equivalent to the Iran-Turanian deserts (according to the concept after Petrov 1965).
The Central Asian desert area of Mongolia and North-China (III) is particularly characterized by the fact that here precipitation from the Asian monsoon regions becomes influent. This gets more significant towards the Eastern part of the region. This phenomenon leads to the most distinctive feature of the Iran-Turanian and Kazakh-Dzungarian deserts: The precipitation maxima in the deserts of Mongolia and North-China (III) are in the summer months, whereas in the Kazakh-Dzungarian (II) and Iran-Turanian deserts (I) the precipitation maxima are during the winter months.
The last of the four desert subregions form the high-altitude deserts in Tibet (IV). Due to their orographic features with mostly more than 4.000 height meters and their basin topography – towards the South bound through the Himalaya and to the West through the Hindu Kush and Pamir – they refer to extremely cold deserts, comparable to the Polar deserts on the polar caps.
The terminology „temperate desert“ includes a variety of different desert types, which indeed are subject of similar climatic conditions, as described above. But there is a multitude of desert types of diverse patches of loam, stone, salt or sand. In general sand deserts are most rich in terms of biodiversity, especially in Karakum and Kyzylkum of Turkmenistan and Uzbekistan. The Karakum is limited by mountain ridges in South and East and changes its character from a plateau to vast plains and a chain of Solonchaks and Takyrs. The Kyzylkum is to the largest extent a vast sand plain with some steep isolated elevations.
Unique feature: Saxaul forests
A unique feature of temperate deserts are Saxaul forests. It covers vast areas in southern Kazakhstan (6 million ha), Turkmenistan (~ 4 million ha) and Uzbekistan (2 million ha). There are two species of Saxaul – white (Haloxylon persicum) and black (Haloxylon aphyllum). These species could be characterized as keystone species for many animals. Saxaul forests are also important for local communities as a source of firewood and most valuable pastures in the desert.