On the Values and Variability of Degree-Day Melting Factor in Finland

About 96,000 snow depth and 17,000 snow density measurements were used to study the most widely used variable in snowmelt forecasting, the degree-day factor. This data was collected on 12 stake stations each with 25 stakes in forest and 9 on open field during 1959 to 1978. The seasonal averages of degree-day factor are studied; they vary rather widely from station to station. The average for all forest sites is 2.42 mm°dC⁻¹d⁻¹ and for all open sites 3.51 mm°C⁻¹d⁻¹. A 10 per cent increase of canopy cover in forest decreases the degree-day factor on the average by 0.16 mm°C⁻¹d⁻¹. On rainy pentades the degree-day factor is larger especially in forest sites. Finally, the seasonal course of the degree-day factor and its dependance on snow density are discussed.