Either condition makes it important to keep your vehicle waxed. The rain picks up all sorts of “stuff” on its way from the clouds to your car. If your vehicle is waxed it prevents the “stuff” from taking up a home in your paint and makes it easy to wash it off.
The drought condition produces intense sunlight and a lot of dust moving around. Sunlight breaks things down (like wax and clear coat) and it burns things (mainly people, but your car is sitting out in it also). The dust is abrasive. Wash it off and put wax on about every 2 months.