To create the effect of wind on your Terrain, you can add one or more GameObjects with Wind Zone components. Trees within a wind zone bend in a realistic animated fashion, and the wind itself moves in pulses to create natural patterns of movement among the trees.
To create a Wind Zone GameObject directly, go to Unity’s top menu and go to GameObject > 3D Object > Wind Zone. You can add the Wind Zone component to any suitable GameObject already in the Scene (menu: Component > Miscellaneous > Wind Zone). The Inspector for the Wind Zone has a number of settings to control its behavior.
For details on all of the Wind Zone settings, see documentation on the Wind Zone component.
You can set the Mode to Directional or Spherical.
The Main property determines the overall strength of the wind, and you can use Turbulence to give these some random variation.
The wind blows over the trees in pulses to create a more natural effect. You can control the strength of the pulses with Pulse Magnitude, and the time interval between them with Pulse Frequency.
The main use of wind is to animate trees, but it can also affect particles in a Particle System if that Particle System uses the External Forces module module. See the Particle System reference page for further details.
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