They have actually already included something like this. They confirmed that if you build too many farms on a river there can be a flood event. I assume there will be other similar events.

I'd really prefer they avoided such seasonal effects, except maybe as in exceptional events ("Your empire has experienced an unusually hard winter recently, with even the wolves coming into villages in search of food" or something along those lines). After all, for a lot of the game the turns will likely comprise several years, so it would feel weird to have such seasonal effects. Why am I getting an effect for a monsoon or for snow on one turn but not the other, when both turns will realistically have had snow or monsoons multiple times during the time the turn spans? They were able to do it in Endless Legend because it was a fantasy world with unusually long seasons, but that excuse doesn't work in a more realistic setting like Humankind.

We're not planning any seasonal effects for Humankind. As Alice99 pointed out, the timescale does not match well with seasons specifically. But we've seen this suggestion come up a lot, so the interest in it is certainly on our mind.

Maybe something along the lines of Winter of Endless Legend - like Dust Bowl or Small Ice age that happened during human history. Those spanned a few years and could be an interesting effect.