Springs feed the Altganat, Urt, Uvurmoilt, Bayan, Tariat, Jargalant and Ust valleys. Some of the springs freeze in winter. The south part of the Tuul River, which is within Hustai National Park (HNP), serves as a water source for nomadic families and their livestock from spring to autumn. During the past few years, the springs’ sources have decreased in volume; some have gone dry. This is likely due to climate change, which is causing more frequent extreme heat in the summer. A geo-hydrological research study published in 2000 reported that HNP’s ground surface decreased by 1 to 1.5 meters in one decade. The loss of birch trees and dried water sources contributed to this change.