Snow cover trends in Finland over 1961–2014 based on gridded snow depth observations

Anna Luomaranta,Juha Aalto,Kirsti Jylhä

doi:10.1002/joc.6007

Anna Luomaranta, Juha Aalto + Show 1 more

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https://doi.org/10.1002/joc.6007

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Abstract

Snow conditions in high‐latitude regions are changing in response to climate warming, and these changes are likely to accelerate as the warming proceeds. Here, we analyse daily gridded snow depth, temperature and precipitation data from Finland over the period 1961–2014 to discover the ongoing changes in monthly average snow depths (SN) and several snow‐related indices. Our results indicate that regional differences of changes in snow conditions can be relatively large, even within such a small district as Finland. Moreover, the interannual variation of the various snow indices was found to be larger in southern Finland than in northern Finland. The largest decrease in snow depth occurred in the southern, western and central parts of Finland in late winter and early spring. This decrease was driven by increasing mixed and liquid precipitation and, especially in spring, increasing temperature. In northern Finland, the decreasing trend of snow depth was most evident in spring, but no change occurred during winter months, although the amount of solid precipitation was found to increase in December–February. In the same months, temperature and the amount of mixed and liquid precipitation increased, likely counteracting the effects of the increasing solid precipitation on snow depth. The annual maximum snow depth that typically occurs in March was found to decrease in over 85% of Finland's area, most strongly in western coastal areas. In almost half of Finland's area, this decrease occurred despite increasing solid precipitation. Our findings highlight the complexity of the responses of snow conditions to climatic variability in northern Europe.

Highlights

Northern European countries such as Finland are highly sensitive to variability and changes in snowfall and snow cover
We examined the role of temperature and precipitation related quantities in controlling snow depth (SN) in these two snow climate regimes in Finland
We found indications that snowfall events may have become more intense in northern Finland as the solid precipitation increased, but ice days, which are the potential days for snowfall to occur, decreased

Summary

Introduction

Northern European countries such as Finland are highly sensitive to variability and changes in snowfall and snow cover. Within the Arctic, the largest decreases in snow water equivalent (SWE) and snow cover duration in recent decades have occurred in maritime regions, including northern Scandinavia (Callaghan et al, 2012). In Europe, the largest percentage reductions in the number of snow cover days and the average SWE are projected to occur in southern and western Europe (Jylhä et al, 2008). In northern Europe, the amount of snow is generally projected to decrease, but the regional and interannual variability is expected to remain high; individual snow-rich winters can still occur in future decades, even where long-term mean SWE is projected to decrease (Räisänen and Eklund, 2012). In northern Fennoscandia, the annual number of snow cover days is projected to decrease most in the coastal regions and least in the mountainous areas (Lehtonen et al, 2013)

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