Transforming Unity Prefabs

I am assuming that these are particle systems? Can you use a script to instantiate a grid of them across the map to attain even and consistent coverage?

Here is the code to do something along these lines. This will produce a grid of 100 x 100 particle systems, spread out by 1 along the x and z axis and 10 on the y axis. Note that this will cause 1000 systems and that may cause a bit of lag. You will need to space and test to determine optimal coverage for you.

 for(int i = 0; i < 100; i++)
 {
     for(int j = 0; j < 100; j++)
     {
         Instantiate(nameOfPrefab, new Vector3(i, 20, j), Quaternion.identity);    
     }
 }

If you would like to keep the particle count down, you can achieve rain by attaching the particle system to your camera. Then it will always seem like its raining. It all depends on what you are trying to accomplish

That would probably work, do have a code I could use?