Why are deserts and semideserts found at the base of parts of the Tien Shan?

The presence of deserts and semideserts at the base of the Tien Shan is primarily a result of the region's sharply continental climate and characteristic aridity. Located in the center of Eurasia, the Tien Shan is subject to extreme temperature fluctuations and limited moisture, which manifest in the surrounding dry regions.1

The aridity is reinforced by the mountain range's geography: while moisture-bearing westerly winds from the Atlantic Ocean provide precipitation to the windward western and northwestern slopes, the interior and eastern regions of the Tien Shan receive significantly less rainfall, often dropping to between 8 and 16 inches annually, and in some places, less than 4 inches. Consequently, these foothills and plains at the base of the mountains develop into semidesert and desert zones, characterized by drought-tolerant vegetation such as wormwood, Ephedra shrubs, and ephemeral grasses that die out as summer begins.12