We do have a weather system!
DoF will have Rain, Snow, Sandstorms, and perhaps even other weather anomolies, both natural and magically created
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Weather does affect units in different ways, archers will get reduced visibility, melee units will get slowed in cold climates. Sandstorms and other weather effects can even harm your units if they aren't properly protected from the elements.
We also have little touches like footprints being left in snow, sand and mud that allow for tracking, or misdirecting. Though with snow and sand, these will be covered over time by snowfall / sand movement.