Hilppa Gregow, Heli Peltola, Mikko Laapas, Seppo Saku, Ari Venäläinen. (2011). Combined occurrence of wind, snow loading and soil frost with implications for risks to forestry in Finland under the current and changing climatic conditions. Silva Fennica vol. 45 no. 1 article id 30. https://doi.org/10.14214/sf.30

Keywords: A1B-scenario; climate change; snow loads; soil frost; stem breakage; uprooting; wind

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This work focuses on the combined occurrence of wind, snow loading and soil frost with implications for risks to forestry in Finland under the current and changing climatic conditions. For this purpose, we employ meteorological datasets, available for the period of 1971–2009 and global climate model (GCM) simulations for the current climate 1971–2000, and periods 2046–65 and 2081–2100 applying the A1B-climate change scenario. Based on our results, the wind and snow induced risks to Finnish forests are projected to increase in the future although the change in the occurrence of strong winds is small. This is because soil frost depths that support tree anchorage from late autumn to early spring in Finland are projected to nearly disappear in the southern and central parts of the country. Heavy snow loads > 30 kg m^–2 are becoming more common in southern and eastern Finland despite that the average cumulative 5-day snow loads decrease in these areas by 18 to 50%, respectively. As a result of the changes in the combined occurrence of wind, snow loading and soil frost, the risk of climatic conditions making conifers liable to uprooting are projected to increase in southern, central and eastern Finland. In the north, the risk of stem breakage is becoming more pronounced under snow loading > 20 kg m^–2. Despite some uncertainties related to this work, we assume that the findings can serve as valuable support for the risk assessment of wind and snow induced damages to Finnish forests and for forestry, in general.

Gregow, Finnish Meteorological Institute, Helsinki, Finland E-mail: hilppa.gregow@fmi.fi
Peltola, University of Eastern Finland, Faculty of Forest Sciences, Joensuu, Finland E-mail: heli.peltola@uef.fi
Laapas, Finnish Meteorological Institute, Helsinki, Finland E-mail: ml@nn.fi
Saku, Finnish Meteorological Institute, Helsinki, Finland E-mail: ss@nn.fi
Venäläinen, Finnish Meteorological Institute, Helsinki, Finland E-mail: av@nn.fi

article id 231, category Research article

Hilppa Gregow, Ulla Puranen, Ari Venäläinen, Heli Peltola, Seppo Kellomäki, David Schultz. (2008). Temporal and spatial occurrence of strong winds and large snow load amounts in Finland during 1961-2000. Silva Fennica vol. 42 no. 4 article id 231. https://doi.org/10.14214/sf.231

Keywords: soil frost; coniferous forest; wind climate; precipitation; snow

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Information on the temporal and spatial occurrence of strong winds and snow loads on trees is important for the risk management of wind- and snow-induced damage. Meteorological measurements made at 19 locations across Finland during 1961–2000 are used to understand the temporal and spatial occurrence of strong winds and large snow loads. A Kriging interpolation method was used to produce a spatial analysis of wind-speed events above 11 m s–1, 14 m s–1, and greater or equal to 17 m s–1 and snowfall accumulation above 20 kg m–2 and 30 kg m–2. According to the analysis, wind speeds exceeded 14 m s–1 at least 155 times and reached 17 m s–1 only 5 times at inland locations during the 40 years. Large snowfall accumulations were more frequent in the higher-elevation inland areas than along the coast. The snow load on trees exceeded 20 kg m–2 about 65 times a year when averaged over all 40 years, but was as high as 150 times a year during the mild 1990s. The maximum number of heavy snow-load events occurred in 1994 in northern Finland, consistent with a forest inventory by the Finnish Forest Research Institute in 1992–1994. The findings of this study imply that the risk of wind-induced damage is highest in the late autumn when trees do not have the additional support of frozen soil. In contrast, the risk of snow-induced damage is highest at higher-elevations inland, especially in northern Finland.

* Erratum (23 Oct 2012): The authors have requested inclusion of an additional author. Author information should thus be as follows: Hilppa Gregow, Ulla Puranen, Ari Venäläinen, Heli Peltola, Seppo Kellomäki & David Schultz

Gregow, Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland E-mail: hilppa.gregow@fmi.fi
Puranen, Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland E-mail: up@nn.fi
Venäläinen, Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland E-mail: av@nn.fi
Peltola, University of Joensuu, Faculty of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: heli.peltola@uef.fi
Kellomäki, University of Joensuu, Faculty of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: seppo.kellomaki@uef.fi
Schultz, Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland E-mail: ds@nn.fi

article id 338, category Research article

Andrea Vajda, Ari Venäläinen, Pekka Hänninen, Raimo Sutinen. (2006). Effect of vegetation on snow cover at the northern timberline: a case study in Finnish Lapland. Silva Fennica vol. 40 no. 2 article id 338. https://doi.org/10.14214/sf.338

Keywords: climate; snow; forest-tundra; Lapland; radar; tree-line; wind modelling

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The presence of permanent snow cover for 200–220 days of the year has a determining role in the energy, hydrological and ecological processes at the climate-driven spruce (Picea abies) timberline in Lapland. Disturbances, such as forest fires or forest harvesting change the vegetation pattern and influence the spatial variation of snow cover. This variability in altered snow conditions (in subarctic Fennoscandia) is still poorly understood. We studied the influence of vegetation on the small-scale spatial variation of snow cover and wind climate in the Tuntsa area that was disturbed by a widespread forest fire in 1960. Radar was applied to measure snow thickness over two vegetation types, the spruce-dominant fire refuge and post-fire treeless tundra. Wind modelling was used to estimate the spatial variation of wind speed and direction. Due to the altered surface roughness and the increased wind velocity, snow drifting was more vigorous on the open tundra, resulting in a 30-cm thinner snow cover and almost half the water equivalent compared to the forest values. The changes in local climate after the fire, particularly in snow cover, may have played an important role in the poor recovery of vegetation: a substantial area is still unforested 40 years after the fire.

Vajda, Finnish Meteorogical Institute, Climate and Global Change, P.O. Box 503, FI-00101 Helsinki, Finland E-mail: andrea.vajda@fmi.fi
Venäläinen, Finnish Meteorogical Institute, Climate and Global Change, P.O. Box 503, FI-00101 Helsinki, Finland E-mail: av@nn.fi
Hänninen, Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland E-mail: ph@nn.fi
Sutinen, Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland E-mail: rs@nn.fi

article id 414, category Research article

Markku Larjavaara, Timo Kuuluvainen, Heidi Tanskanen, Ari Venäläinen. (2004). Variation in forest fire ignition probability in Finland. Silva Fennica vol. 38 no. 3 article id 414. https://doi.org/10.14214/sf.414

Keywords: ignition; forest fuel moisture; forest fire; fire regime

Abstract | View details | Full text in PDF | Author Info

We examined climate-caused spatio-temporal variation of forest fire ignition probability in Finland based on empirical ignition experiments and 37 years of meteorological data from 26 meteorological stations scattered across Finland. First, meteorological data was used in order to estimate the variation in forest fuel moisture content with the model of the Finnish forest fire risk index. Second, based on data from empirical ignition experiments, fuel moisture content was linked with forest fire ignition probability. In southern Finland average forest fire ignition probability typically peaks in late May and early June, whereas in the northern part of the country the peak occurs at the end of June. There was a three-fold difference in the average annual ignition probability between the north-eastern part (3%) and south-western part of the country (9%). The observed differences in fire ignition probability suggest that the characteristics of the natural fire regime also vary considerably in the southern versus the northern part of the country.

Larjavaara, University of Helsinki, Dept of Forest Ecology, FI-00014 University of Helsinki, Finland E-mail: markku.larjavaara@helsinki.fi
Kuuluvainen, University of Helsinki, Dept of Forest Ecology, FI-00014 University of Helsinki, Finland E-mail: tk@nn.fi
Tanskanen, University of Helsinki, Dept of Forest Ecology, FI-00014 University of Helsinki, Finland E-mail: ht@nn.fi
Venäläinen, University of Helsinki, Dept of Forest Ecology, FI-00014 University of Helsinki, Finland E-mail: av@nn.fi

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