*4.1. Snow Cover Analysis*

The snow cover analysis from MOD10A2 data in Figure 6 shows that a large portion of the study area was covered by snow, while the SCDr varied across the area. Statistically, the SCDr in 52.27% of the study area was higher than 40%, and the SCDr was lower than 20% only in 21.25% of the study area.

**Figure 6.** The derived SCDr map in the study area. SCDr is the ratio of days with snow to total days from DOY 001 to DOY 208.

Statistically, approximately 77% of the study area has an elevation ≥ 4000 m, while only approximately 6% of the area has an elevation < 3500 m. Figure 7 shows the statistical distributions of ESS, SCDr, and SCDc in each elevation zone. In all four elevation zones, the ESS values were concentrated on DOY 136. The increase in elevation led to the increase in ESS. When the elevation increased to ≥4000 m, a significant subpeak in the ESS appeared on DOY 160. Both SCDr and SCDc increased with increasing elevation. The peak values of SCDr were 0%, 8%, 36%, and 64%, while the peak values of SCDc were 8, 8, 16, and 88 days, respectively, for all four elevation zones from elevations <3500 m to ≥4500 m.

**Figure 7.** Statistical distributions of (**a**) ESS, (**b**) SCDr, and (**c**) SCDc in each elevation zone.
