ForestGALES - Wind Risk Decision Support Tool

How ForestGALES works - Calculating wind risk

ForestGALES operates within a standard risk framework whereby risk is defined as the interplay between the vulnerability of a system and the hazard it is exposed to. Risk is therefore calculated in two stages. Firstly, the vulnerability of trees to wind damage is computed as the critical wind speed at which trees will be damaged, either by uprooting or stem breakage. Secondly, the localised wind climate is derived to represent the wind hazard. Multiple ways exist to characterise wind climates. Traditionally and most commonly, this is done with a Weibull distribution of mean wind speeds in a specific location. In British forestry, the DAMS windiness score was developed to provide an accessible interpretation of the Weibull distribution of wind speeds. Risk is then defined as the probability of exceeding the calculated critical wind speeds given the localised wind climate. The return periods of damaging storms based on stand location can then be calculated from this probability. ForestGALES calculates the vulnerability to wind damage using information from the trees including: species, height, stem diameter, age (to estimate height and diameter when not known directly) and then the site including: soil type, rooting depth, spacing between trees, thinning, type of forest edge (acclimated or ‘green’ vs unacclimated or ‘brown’).