You know, I wonder this myself. We are not told at all in the book HOW they have managed to get rid of variations in the weather. All we really know is that they have done it.
There is a lot we do not know about how the society works. We do not really know how they get their food or anything like that. We don't know where the other communities are and what sort of a government they have.
My guess is that there is some sort of overall government that has managed to control the weather. There must be an overall government because there are other communities that have pretty much the same rules. So someone must be coordinating the whole thing and that government must have been the one that took control of the weather.