Estimate_Gust_velocity

As shown below the gust speed likely to cause lodging is calculated from the mean hourly speed. Thus wath is ideally required is the probability distribution of the maximum hourly mean wind speed that can be expected to occur in any one day.

Even if data for this are not directly available the probability Pw that the hourly mean win speed will exceed a certain value V is given by the Weibull distribution.

To attain this V values of relevance to the lodging problem, V must be transformed with correction factors to allow the difference between hourly mean wind speed and daily maximum hourly mean wind speed. The expressions used for adaptation are:

where Vhourly is the hourly wind speed, V1m the wind speed 1 meter above the canopy, Vmeasured the wind speed at the height where wind is measured and z0 is the roughness length calculated as follows:

This parameter represents the bulk effect of the canopy on wind speed.

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