Why do the inner and eastern Tien Shan receive less precipitation?

The inner and eastern regions of the Tien Shan receive significantly less precipitation primarily due to the barrier effect of the mountains themselves.

Moisture-bearing westerly winds from the Atlantic Ocean transport air masses across the range, but the majority of this moisture is deposited on the windward western and northwestern slopes. As these winds move further into the interior and toward the east, the mountains act as a physical barrier, isolating these regions from the moisture-laden air. Consequently, the inner and eastern areas lie in a rain shadow, where the air is significantly drier.12

Additionally, the topography contributes to the foehn effect, where air descending leeward slopes is warmed and dried, further reducing the likelihood of precipitation in these interior basins. While western and northern areas receive most of their rain during the warm season, the inner and eastern regions experience very low annual totals, often ranging between 8 and 16 inches, and in some locations, less than 4 inches.21