Abstract
Abstract. Windstorms are natural disturbance agents in forests playing a role in natural forest regeneration. In Finland, the most severe individual windstorms have commonly damaged 2–4 million m3 of timber. In addition to financial losses caused to forest owners, windthrown trees have in many cases seriously disrupted the functionality of the national power grid. Communicating windstorm risks in duty forecasting is difficult. In this study, we aimed at developing windstorm impact estimates for forest damage in Finland to help the forecaster to improve communication of the risks of windstorms. We have compared the volume of forest damage caused by the most intense windstorms in Finland during the recent decade to the observed maximum inland wind gust speeds associated with the same windstorms. It was found out that the volume of forest damage follows approximately a power relation as a function of wind gust speed with a power of ∼10. This is a tentative estimate because of a short time series and small number of inspected windstorms. Moreover, also wind direction, location of the affected area and soil properties among other factors have an impact to the amount of damage as illustrated in our inspection. Despite the shortness of the time series, we believe that our results demonstrating the steep increase in the impacts of windstorms with an increasing windstorm intensity are valuable. However, more detailed investigations with longer time series are needed in order to more specifically communicate the windstorm risks and their impacts in boreal forests.
Highlights
Windstorms are among the most hazardous abiotic disturbances affecting the northern European forests (Schelhaas et al, 2003; Kuuluvainen and Aakala, 2011; Mitchell, 2012; Gardiner et al, 2013; Gregow et al, 2017)
Our results show that the volume of wind-induced forest damage in Finland can conditionally be estimated based on a simple power relation as a function of WGmax
The power relation is applicable for large-scale windstorms that affect southern, western and eastern parts of Finland when: (1) the wind direction is between west and northwest, (2) the WGmax ranges between 25–32 m s−1, (3) the soil is not frozen, and (4) the deciduous trees are without leaves
Summary
Windstorms are among the most hazardous abiotic disturbances affecting the northern European forests (Schelhaas et al, 2003; Kuuluvainen and Aakala, 2011; Mitchell, 2012; Gardiner et al, 2013; Gregow et al, 2017). It was argued that year 1990 represents a change-point after which the windstorm induced large-scale forest damage have increased by a factor of three in Europe (Gregow et al, 2017). In Finland, approximately 10–25 large scale windstorms occur every year but usually only a few of them are severe. Typical to the most severe large-scale storms in Finland is that the mean wind speeds over the marine and coastal stations have been above 25 m s−1 (Gregow et al, 2008)
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