“ At regular intervals, a god takes control of your world's weather. Choose the gods at random each turn of the interval and begin applying their effects subtly. Their power will depend on the strength of those who worship them.
For civilised people, worship of a god actually wanes during that god's month in an effort to reduce their potential destructive effect.”
“ A desolate region is almost entirely without normal vegetation. Local plants are able to unroot themselves and crawl along the ground in search of water and fertile soil. The inhabitants fence their crops in to keep them from wandering off and put heavy stone thresholds in the doorways of their huts to keep wayward plants out.
The plants sense by chemical cues, lacking sight or hearing, and tend to avoid herbivores or anything that smells of 'dead plants'. Characters with horses are likely to be unwelcome among the locals.”
“ A common mistake when writing adventures set in deserts is to assume that the climate is too ferociously hot to wear armor. Historically, most battles in deserts involved troops dressed in protective armor. Although they would have been miserable during the hottest part of the day or the hottest part of the year, desert weather isn't intolerably hot 24/7.”