Abstract: The northern piedmont of the Tianshan Mountains and the southern marginal zone of Junggar Basin are the regions with the most developed economy in Xinjiang. However, the frequent occurrence of spring floods caused by snowmelt water threatens directly the safety of the communications and traffic facilities, reservoirs, irrigation canals, water conservancy and hydropower works, and even people's life and property in north Xinjiang. Starting from the formation causes, this paper analyzes the 5 main factors resulting in the spring floods caused by snowmelt water in the Sangong River watershed. The 5 main factors include the precipitation during the stable snow-cover period, precipitation within 25 days before the stable snow-cover day, precipitation within 25～85 days before the stable snow-cover day, the three-day accumulated temperature before the stable snow-cover day, and the change of the winter negative accumulated temperature related to the vegetation conditions in the watershed and the climate warming. Among which the winter negative accumulated temperature changes the area and the intensity of the impervious and poor-pervious strata, cuts off and reduce the pathways of permeation of snow melt water. The purposes of the study are to research the mechanism of the formation causes of spring floods caused by snow melt water in the low-mountain and hill regions of northern piedmont of the Tianshan Mountains and to develop the prediction models.

Key words: northern piedmont of the Tianshan Mountains, low-mountain and hill regions, flood caused by snowmelt water, underlying surface, permeation intensity