Less snow

Warmer climate means thinner snow cover and shorter snow cover season. In southern and western Finland, the number of snow cover days may decrease to less than one half of the present level. Even though the snow cover decreases on average, winters with abundant snow will be seen in future, too, but they will become less frequent in time.

Thinner snow cover and less snow cover days

In a warmer climate, winter precipitation is more water than snow. Simultaneously, thaw becomes more common which means that snow melts away. Figure 1 shows a model prediction of changes in the number of snow cover days and water equivalent of snow. The water equivalent of snow describes well the depth and mass of snow.[1]

In southern Finland, the number of snow cover days may decrease to less than one half within a hundred years (upper map in figure 1). The average mass of snow cover would decrease even more, by 80-90% (lower map in figure 1).

The increasing amount of precipitation in northern Finland in the winter months will partly compensate the impact of warming. The snow cover will not decrease as drastically there as down south. However, the number of snow cover days would decrease by 20-30% even in northern Finland, while 40-70% of snow cover mass would be lost.

Change in number of snow cover days

Change in water equivalent of snow

Figure 1. Change in number of snow cover days predicted by the regional climate model (upper figure) and change in average water equivalent of snow (lower figure). Both illustrations show percentual change from the period 1961-1990 to 2070-2099, assuming that greenhouse gas concentrations are in line with the pessimistic scenario A2.

Permanent snow cover only in Lapland at the end of the century

Particularly southern and western Finland will only see periodic snow in winter in future, similarly to the current situation in November. However, individual severe snowstorms that disrupt the functions of society will be occasionally seen in future, too. In most cases, however, the snow will soon melt away.[2][3]

Lapland would at least have permanent snow in winter even at the end of the century, even if the snow cover season would be shorter at both ends, autumn and spring.

Uncertain predictions on the amount of snow

The projections given are based on the pessimistic greenhouse gas scenario A2. If we succeed in restricting emissions, the future would not have quite that little snow. However, the differences between scenarios will not become evident until around mid-century and thereafter.

In practical terms, different models simulate the intensity of warming and changes in precipitation differently. This introduces a certain element of uncertainty to the rate at which snow reduces.

Even if warming follows the medium scenarios (A1B), the amount of snow will decrease already in the next few decades. Even though the snow cover decreases on average, winters with abundant snow will be seen in future, too, but they will become less frequent in time. The capricious behaviour of snow cover will be more evident in southern than northern Finland.

References

  1. Jylhä, K., Ruosteenoja, K., Räisänen, J., Venäläinen, A., Ruokolainen, L., Saku, S. ja Seitola, T., Arvioita Suomen muuttuvasta ilmastosta sopeutumistutkimuksia varten, ACCLIM-hankkeen raportti 2009. https://helda.helsinki.fi/bitstream/handle/10138/15711/2009nro4.pdf?sequence=1
  2. ACCLIM II-hankkeen lyhyt loppuraportti http://ilmatieteenlaitos.fi/c/document_library/get_file?uuid=f72ce783-0bae-4468-b67e-8e280bec1452&groupId=30106
  3. Räisänen, J. and J. Eklund, 2011: 21st century changes in snow climate in Northern Europe as simulated by regional climate models in the ENSEMBLES project: a high-resolution view from ENSEMBLES regional climate models. Climate Dynamics, DOI: 10.1007/s00382-011-1076-3. http://www.springerlink.com/content/rpl8774t63760n13/

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