Field Observations of the Effects of Various Widths and Densities of Shelterbelts on Wind Speed Distribution.

To clarify the effects of the width and density of a shelterbelt on wind speed reduction, field observations of wind speed distribution were carried out around shelterbelts of different widths and plant area densities (PADs). The results are as follows.(1) For shelterbelts with the same width, the wind speed on the leeward of the shelterbelt decreased as PAD increased. On the other hand, for shelterbelts with the same PAD, the wind speed on the leeward of the shelterbelt decreased as the width increased. Consequently, width and PAD were confirmed to be factors of the shelterbelt structure that influence wind speed.(2) In the relationships between the minimum wind speed and width or PAD, there were great variations in the data. However, a strong correlation was found between the minimum wind speed and HPAI, determined as the total surface area of plants (one side only) within a horizontal cylinder of unit cross-section. Consequently, HPAI is a valid factor with which to evaluate the effects of shelterbelt structure on wind speed.