TL;DRPollution creating natural disasters that can damage or even destroy bases, trees, rocks and enemies (and anything else that is destructible). Uranium ammo and atomic bombs could cause pollution on hit.
What ?An animated sprite that could be used for various disasters of various magnitudes. These animated sprites would spawn on the outskirts of a pollution cloud (if enough pollution is present) and slowly move towards the center (or towards sources of pollution) in somewhat erratic paths. Their effects would be emulated by the sprites firing invisible projectiles at anything within their "weapon" range, though there may be room for more animation artwork here regarding on-hit effects (their effects could probably be emulated in a different fashion, this is merely an idea).
Their life time, size and damage depends on the severity of the pollution (more details below).
Spawning chance (per game-tick) depends on number of tiles with the respective severity of pollution (for balancing reasons, depending whether spawning chance works per game tick or otherwise, the chance for disasters to spawn should be very low). Maybe something like - Spawning chance (in percent) = number of tiles with respective pollution x .0001 or something.
An option or slider in the map generation menu to adjust the criteria for disasters to spawn and the option to deactivate them entirely
Types of disasters:
Thunder Storm (spawning criteria: high local pollution per game-tick, cannot spawn if pollution is too low)
- deals minor damage only, not enough to actually destroy anything but has a high life time and slow movement speed. dissipates after moving to a certain number of low pollution or unpolluted tiles or after a certain amount of time has passed (time limit)
Tornado (spawning criteria: extreme local pollution per game-tick, cannot spawn if pollution is too low)
- deals moderate damage over a small area. moderate movement speed, high life time. dissipates only after entering a certain amount of moderate pollution, low pollution or unpolluted tiles (no time limit)
Hurricane (spawning criteria: maximum local pollution per game tick, cannot spawn if pollution is too low)
- a very large hurricane. deals moderate damage across a very large area. Very slow movement speed, very high life time. dissipates only after entering a certain amount of high pollution tiles or an extensive amount of moderate pollution, low pollution or unpolluted tiles (no time limit)
Uranium Ammo and Atomic bombs could cause pollution wherever it strikes (similar to the flame thrower but with more pollution generated for a longer time) which could give an interesting aspect of effectively "irradiating" a piece of land for an amount of time causing and drawing natural disasters to that region.