Long-term variability and trends in annual snowfall/total precipitation ratio in Finland and the role of atmospheric circulation patterns

This study evaluated variabilities and trends in annual snowfall to total precipitation (S/P) ratio at Sodankyla, Kajaani and Kaisaniemi weather stations in northern, central and southern Finland during 1909-2008. Annual S/ P ratio was estimated using daily precipitation and temperature records as input to a calibrated and validated temperature-index snowmelt model developed to simulate snowpack accumulation and melt processes in Finland. Factors controlling variations in annual S/P ratio and their relationships with large-scale atmospheric circulation patterns (ACPs) were also studied. The results show that there were significant declines in annual S/P ratio during 1909-2008, which were principally attributable to century-long decreasing trends in annual snowfall (S) in Finland. These reductions in annual S were predominantly controlled by both annual rainfall (R) and snowfall-day temperature (ST) in the south, annual ST in the centre, and annual R in the north. However, dividing the 100-year study period into an early (1909-1958) and late (1959-2008) periods revealed non-linear trend behaviours in annual S and consequently annual S/P ratio during 1909-2008. The Arctic Oscillation, East Atlantic, East Atlantic/West Russia and Scandinavia patterns were the most influential ACPs for annual S variability.