Valleys colder than peaks
In the Talas Alatau range of the Western Tien Shan mountains, topography creates a strange atmospheric phenomenon. On clear, calm nights, cold, dense air from the high slopes drains downwards, pooling in the deep valleys of the Aksu-Zhabagly Nature Reserve. This process, called katabatic drainage, results in powerful temperature inversions. The valley floor can become significantly colder than the surrounding peaks, with recorded temperature differences as high as 20°C. These "frost hollows" or "cold pools" effectively create pockets of high-altitude climate at much lower elevations.
The reserve's landscape, which ranges from 1,100 to 4,236 meters, is defined by this extreme continental climate. The deep Aksu Canyon, with walls plunging 500 meters, is a prime example of the terrain that traps this cold air. While the average July temperature in the foothills can reach 21.6°C, these cold air pools maintain conditions suitable for life forms usually found thousands of meters higher. This natural refrigeration allows the persistence of species that would otherwise have vanished from the area thousands of years ago.
Botanical time capsules
The most significant consequence of these frost hollows is their effect on the local flora. They serve as micro-refugia for arctic-alpine plant species, remnants from the last glacial period. As the climate warmed, these cold-adapted plants retreated to higher, colder altitudes. In Aksu-Zhabagly, however, populations became stranded in the refrigerated valleys. Here they grow as much as 2,000 meters below their typical elevation range.
Botanical surveys have identified numerous of these relict species. One notable example is Oxygraphis glacialis, a small, yellow-flowering plant typically found in alpine meadows above 3,000 meters. In these frost hollows, it thrives at far lower altitudes, evidence of a past climate. The reserve contains 1,312 vascular plant species in total, including many endemic and rare plants. The unique ecosystems created by the temperature inversions contribute to the area's designation as part of the Western Tien-Shan UNESCO World Heritage Site, which is recognized as a global center for agrobiodiversity and the origin of many cultivated fruits.