Modelling crown snow loads in Finland: a comparison of two methods

• Published in: Silva Fennica
• Main Authors: Lehtonen, Ilari, Hoppula, Petri, Pirinen, Pentti, Gregow, Hilppa
• Format: Article in Journal/Newspaper
• Language: English
• Published: Finnish Society of Forest Science 2014
• Subjects: Forestry; SD1-669.5; Rime; Northern Finland
• Online Access: https://doi.org/10.14214/sf.1120; https://doaj.org/article/8ca63eec781646aab69ece9de1bc6382

The spatial occurrence of heavy crown snow loads in Finland between 1961 and 2010 is studied by using for the first time a model that classifies the snow load into four different types: rime, dry snow, wet snow and frozen snow. In producing this climatology, we used meteorological observations made at 29 locations across Finland. The model performance is evaluated against classified daily images of canopy snow cover and with the help of two short case studies. The results are further compared to those achieved with a simpler method used in previous studies. The heaviest crown snow loads are found to occur typically in eastern Finland. The new method reveals that this holds not only for the total snow loads but also for the different snow load types, although there are certain differences in their geographical occurrence. The greatest benefit achieved with the new method is the inclusion of rime accretion. The forests most prone to heavy riming are those located on tree-covered hills in northern Finland, but as the terrain elevation affects riming efficiency greatly, these small-scale variations in the snow load amounts could not be described in this study in great detail. Moreover, the results are more inaccurate in northern Finland where variations in the terrain elevation are greater than elsewhere. Otherwise, the largest uncertainties in this study are related to wind speed measurements and possibly partly because of that, we were not able to detect any significant trends in the crown snow-load amounts over the study period.