Also less humid air

Does water already in vapor form really impact fires?

It appears humidity doesn't really impact an already burning wildfire, but lower humidity means drier fuel which makes the fire more likely to spread. Conversely, higher humidity can make a fire less likely to spread to moister fuel[1]

[1]http://www.auburn.edu/academic/forestry_wildlife/fire/relati...

Peat itself is often fairly damp.