Basically dry/hot weather only makes fires worse, but dry weather doesn’t start fires.
Depending on the time of year, 17-27% of structure (buildings) fires are caused by heating, like heaters and fireplaces.
For wilderness fires, 80% of them are caused by humans and the fires spread faster because of hot weather.
Lightning strikes the earth about 100,000 times a day, 10-20% of those lightning strikes cause fires. These fires also spread faster when combined with hot weather.