In approximately half of the herding districts in Finland, basal ice events occurred more frequently in the period 1983–2016 than in the period 1948–1982. Researchers collected practitioners’ knowledge of herders from the period 1948–2016. During this period, seven winters with extensive basal ice formation were identified. Five out of seven of the most extensive basal ice formation events occurred between 1991 and 2016. Approximately one fourth of all reported mold formation events co-occurred with basal ice formation.

Basal ice formation in the terrestrial snow cover is a common
phenomenon in northern circumpolar areas, one having significant impacts on
ecosystems, vegetation, animals and human activities. Basal ice forming early in the
winter and lasting for prolonged time is a significant risk for reindeer grazing
increasing winter mortality and the need for the supplementary winter feeding, and
decreasing the calving success during the subsequent spring. Another risk factor
associated with warm and rainy early winters is the growth of mycotoxin-producing
molds below the snow.

Processes contributing to basal ice
formation, such as thaw or rain and the subsequent freezing of the snow cover, may
occur more often in the future because of warmer winters and more frequent extreme
warm events. There is limited knowledge on the spatial and temporal occurrence of
basal ice formation because of the sparse observation network and challenges
involved in detecting formation events. Also knowledge on the prevalence and
frequency of mold formation, its relation to weather conditions and potential
co-occurrence with basal ice events is poor. Researchers have now presented a unique
dataset on the annual extent of ice formation events in northern Finland between
1948 and 2016 based on reindeer herders’ descriptions of the cold season in their
management reports.

Extreme years are difficult to
distinguish using only seasonal means of meteorological observations or large-scale
atmospheric teleconnections such as the North Atlantic Oscillation. Thorough
analysis of local and short-lived weather events or simulation of snow cover
stratigraphy will be required before detailed explanation of these ice formation
events will be possible.

Results have been reported in an
international journal Environmental Research Letters. Research was carried out by
Sirpa Rasmus from the Arctic Centre at the University
of Lapland (Finland), Sonja Kivinen from the University
of Eastern Finland and Masoud Irannezhad form Southern
University of Science and Technology (China). The work was funded through NCoE ReiGN
by NordForsk.

More
information:

Sirpa Rasmus
Arctic
Centre, University of Lapland
040 528 2585,
sirpa.rasmus@ulapland.fi

Sonja Kivinen
University of Eastern Finland
040 588 4185, sonja.kivinen@uef.fi

Rasmus, S., Kivinen, S., Irannezhad, M. 2018. Basal ice
formation in snow cover in Northern Finland between 1948 and 2016. Environ. Res.
Lett. 13. 114009. http://iopscience.iop.org/article/10.1088/1748-9326/aae541/pdf

LaY/AK/JW
Photo: Ilona Mettiäinen