**2. Study Area**

Northeast China is located at 115◦30~135◦60E, 38◦42~53◦36N, and the area is approximately 1.24 million km2. The whole region is surrounded by the Daxingan Mountains, Xiaoxingan Mountains, and Chang-bai Mountains, with the Northeast Plain in the middle. It is a relatively independent and complete natural geographical area (Figure 1). The annual average temperature, precipitation, and elevation are −5~11 ◦C, 300~1000 mm, and 443 m, respectively [27–29]. Due to the existence of large-scale forests and climate factors, this region in China has a long snow period and thick snow cover [30]. The Daxingan Mountains, Xiaoxingan Mountains, and Changbai Mountains are the most important snowfall areas, with an average annual snowfall of more than 60 mm. The average snowfall is more than 90 mm in the northern Daxingan Mountains and Changbai Mountains, while in some plain areas, the average snowfall is less than 30 mm [31]. Here, the snowfall means the snow water equivalent.

**Figure 1.** Topography and station distribution in the study area.
