Because the water on the track greatly reduces the traction, it becomes the most important factor. Anthing you can do to improve the tire's ability to stay connected to the road surface is done. But time constraints, the regulations, and having to weight the decision on a dry or wet setup.
The engine is retued to deliver a smoother, less harsh torque delivery to the drivtrain. With modern engine electronic control units, this is easily done. The engine probably makes less top end power, but the peak power doesn't come on so suddenly, and the risk of the rear wheels breaking loose is reduced. And of course, traction control is used. Interestingly, traction control is very hard on the engine, and can lead to a shortened life.
On the suspension side you want to make sure the car will never ground out,so usually it rides higher than a dry track setup. Larger diameter wet tires is that solution. The setup used in qualifying is supposed to remain unchanged for the race, so the engineers and tacticians spend countless agonizing hours trying to forecast the weather. A lot of money is spent on forecasting every anticipated weather event, and in fact before this race in China, almost all the private jets owned and used by the drivers and race teams will be in the air, circling around the track, scouting every weather change
If you decide to setup for rain, you crank in maximum downforce with the wings. The suspension is softer, more supple, and has more travel to give as smooth and forgiving treatment to the tires as possible.
Pure rain tires have an incredibly soft compound, they have to be to give as much traction as possible. In fact, the rubber is so soft that if not cooled by the water, their life expentancy can be as short as three laps. Because of the rain grooves, and soft compound, the tread blocks squirm much more than dry tires, and generate much more heat.
Thr drivers wear their lucky socks, and Flavio has probably contracted every rain making service in the area to keep the clouds seeded and do everything possible to avoid a dry track.
