WMOD00469

• Title: Environmental Impact of Large Windpower Farms
• Weather Modification - Doc Type: Report

In 1 i ght to moderate wi nd, the effects of surface roughness arl~
relatively trivial. When the wind is strong, a windfarm would
tend to increase the rate at which air within a few tens of
meters of the ground mixes with air at higher levels up to a
height of as much as 1.5 km, depending upon the strength of the
wind and the distribution of temperature aloft. The roughness
also decreases the average speed within the turbulent layer.
Windfarms will cause some decrease in average windspeed and some
increase in turbulence above a few tens of meters with relatively
little effect closer to the ground where the air is turbulent
anyway whenever the wind is strong.

The increased turbulence through a considerable depth above the
ground tends also toward a somewhat more even distribution of
potential temperature during episodes of strong wind. The range
of temperature variation would therefore be somewhat decreased at
such times. Since the moisture content of the air near the
ground normally decreases upward, the mixing would tend to
decrease the relative humidity slightly next to the ground and
perhaps increase it slightly at the top of the mixing layer
several hundred meters above the ground.

Precipitation from large storm systems, either winter storms or
large organized systems of convective clouds in summertime, arE~
almost entirely unaffected by local changes in surface roughness
associated with windfarms. During the weather conditions that
make for small, scattered summertime showers, it is conceivable
that the braking effect on the windfarm on the airstream crossing
over it could lead to slight local convergence along the upwind
border of the windfarm, which would tend to promote the growth of
clouds. However, this effect is expected to be so small that it
would be very difficult to verify.

By somewhat decreasing the windspeed near the ground during
episodes of strong winds, windfarms will tend to reduce the
amount of blowing dust and thus to improve air quality. Realization
of thi s improvement, however, will requi re that normal groundcover
be restored to ground disturbed during the construction phase.
Any effect on water quality will likewise be dependent on
control of runoff from disturbed ground during the construction
phase and to restoration of groundcover.

b. Wildlife. - The types of wildlife to be considered in assessing
the impact of large windfarms are large mammals and birds. Other
wildlife, including small mammals, reptiles, and insects, are
unlikely to be affected by windfarms except for temporary
displacement during the construction phase.

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