Quoted from: Singh, Purushottam Raj, Thian Yew Gan, and Adam Kenea Gobena. "Evaluating a hierarchy of snowmelt models at a watershed in the Canadian Prairies." Journal of Geophysical Research: Atmospheres 114, no. D4 (2009). https://doi.org/10.1029/2008JD010597
The standard temperature index method (TI or SDSM‐TI) relates snowmelt rate (m in mm d−1) to air temperature (Ta) through a melt factor (Mf in mm d−1 C−1) as
where Tthm is a melt‐threshold temperature and (Ta − Tthm) is an empirical index of the total amount of insolation received on a regional basis. The TI method works well only when there is a strong correlation between Ta and the dominant energy responsible for snowmelt. Mf depends on the slope, aspect of the land surface, vegetation cover, and climate. Besides seasonal variations due to increase in radiation and decrease in albedo as the season progresses, Mf also varies from year to year depending on annual climatic conditions; for example, Granger and Male [1978] reported Mf values of 8, 5 and 3 mm d−1 °C−1 for 1974, 1975, and 1976, respectively, for an open area located at about 51°N in the Canadian Prairies. Variations in optimized Mf from year to year were also reported by Kane et al. [1997].