Hi, Yep, there's Desert terrain like: well, er, Desert , Desert Depressions, Dunes, Qattara Depression and there's also March, Woods, Groves, Mountain, Mountain Peaks (inaccessible except for road), Rough, and Stoney.
Those terrains can contain Towns, Forts, Entrenchments, and/or Woods.
And for hexsides there's Rivers, Gullies, Mines, Wire, Escarpments, and Ridges.
So Desert is really just "Clear terrain", so you could mod to Siberia but the clear terrain will be called Desert. You can also change the images to make it look like snow of course.
Hope this helps!