As others have mentioned they already do that to a degree they can with the uncertainty of forcast. It’s called Forcast Informed Reservoir Operation (FIRO).
Important thing is that the forecast is uncertain farther you go in future, and smaller the area you’re looking at. So the policies will have to take that into account, you can’t simply empty your reservoir because if your forcast is wrong and you don’t get enough rain, then you don’t have the precious water anymore for dry season. But if you’re wrong on the other side you get flood issue.
Satellite data and a lot of ground sensors are in place that help us better forcast the future storms along with improved computation and technology, but nothing is sure, and it might get worse with current situation. We already have problems because of previous funding cuts causing us to lose so many sensors.
Also a fun fact, we’ve had dams for so long that we don’t know the natural flows for so many rivers so we can’t calibrate our models well. Basically we built dams long before we started measuring the rivers. I’ve been meaning to publish this, but it’s just stuck in a draft for almost a year now :(
Flood control is very close to my area of research. My research involves effect of dams on river water and I don’t get to talk about it often, so it was fun. But I haven’t actually worked on a dam control or made policies, so my work is more theoretical what ifs.