forum.freeciv.org

tornados, earthquakes, hurricanes, volcanoes that actually sprout up and spew lava tiles and lava rivers etc. sinkholes tsunami's nuclear meltdowns meteor strikes red tide, seeing city's get black and dirty and smokey and covered in quarantine tape when there is pestilence or plague, riots, all that...
actually being able to see these things on the map as a part of the landscape as they happen. disasters that actually alter the geography of the map.

giant monster attacks, zombie infection ( can be used to attack other nations )? haha... those could be "funny options" that you can enable if you want.

The issue is that disasters generally last only a short time and/or do not have a large range of effect. Riots, Fallout, and Pollution /do/ appear, after all, and they're the ones with persistent mechanical effects. (Plague, for example, just kills people and empties the foodbox, then it has no further effect)