3.3.1. Snow Cover Analysis

Four parameters were used to describe the coverage and phenology of snow, including SCF, SCDc, SCDr, and ESS. The SCF is defined as the snow cover fraction at each location. The SCDc and SCDr are complementary parameters used to describe snow cover duration. The SCDc denotes the maximum number of consecutive days with snow cover and is more specific, while SCDr is defined as the ratio of days with snow to total days and is more general. The SCDc is more ready-to-use in simulating different snow scenarios if we only consider the longest snow duration, while the SCDr is difficult to simulate, as the spring snow cover might include several periods of snow duration. Thus, SCDc was used in both simulations and satellite data analysis, and SCDr was only used in satellite data analysis. The ESS is defined as the ending date of snow, i.e., the last day with snow cover. Since our focus is spring phenology, the SCDc, SCDr, and ESS were calculated for the period from the day of year (DOY) 001 to 208. The four parameters were calculated from the MOD10A2 snow cover data to reveal the spatial and temporal characteristics of snow in the study area. Furthermore, they were also used in simulation experiments to generate different snow scenarios.
