Storms/tornadoes/typhoons should not be modelled in a game where a turn can be anything from a month to a decade. They should be a random event that destroys a building or two, and/or kills a population at earlier tech levels before civil planning etc come into play to protect cities from them. Volcano makes sense because they sometimes can remain active for years. But even the heaviest storms are over in 2-3 days. Makes no sense to have storms in a game with this scope.
There is an alternative way to deal with the time issue. At least there was in the Genetic Era Mod. If we implement these kinds of events we will use a similar method of dealing with passage of time as in that mod. It will
not be based on turns, but rather the passage of time. We will probably implement a minimum number of turns before the next event as well since even with the odds based on number of years since the last turn, those odds will stack up during the prehistoric era.
The amount of time it takes is irrelevant. They still have a major impact on society. Hurricanes have been known to completely wipe out a city in ancient times. What's worse.... using this same logic, volcanoes
DON'T make sense because the kind of volcanoes that actually do serious damage (strata/composite volcanoes) do not erupt every day, week, or even years. If they did, they would not be so violent. Instead hundreds and thousands of years pass between eruptions and those eruptions take hours or minutes to erupt which is considerably less than days. Earthquakes take seconds. Yet both of those are still game events.
EDIT: To help you understand the above facts regarding volcanoes I will explain a little deeper. There are three kinds of volcanoes: Fissure/shield volcanoes are the kinds you find in Hawaii and Iceland. They have runny lava, are tame and rarely do any damage to civilization because their eruptions aren't big, eruption flow is usually consistent, and civilization usually avoids building things in the path of these eruptions/lava flows. These kind of eruptions can occur frequently (daily, weekly, monthly) but don't have too.
The second kind of volcano is at the other extreme: Strata volcanoes (also called composite volcanoes). These are the BIG, destructive eruptions. The volcanoes literally explode, sending volcanic bombs (large rocks, yes... that is what they are called) and ash into the air. Some of this ash can remain aloft and land in places thousands of miles away. The initial explosion is quickly followed by ash flows which get ejected everywhere. An ash flow can reach speeds of 150 miles per hour and flow for 10s of miles, burning and burying everything in its path. Their paths are completely unpredictable. Water usually exists nearby in the form of springs. This can mix with the ash and turn to fast mod flows which can extend the damage even further.
These are the kind of eruptions I am talking about above. A single volcano can go tens of thousands of years without eruption and then suddently erupt. The reason for this is because the lava is VERY thick and blocky. The thick blocky lava covers the eruption hole and forms a vast plug which is VERY difficult to break through (tons of rock). The pressure has to build up over hundreds and thousands of years before it will erupt again.
The third type of eruption is between both of these extremes and is called a cinder cone. This kind of eruption is not as predictable as shield volcanoes but they are small volcanoes and their eruption will only affect the surrounding mile or two. With these eruptions, the volcano spews cinders (they look like sparks but are actually small pieces of rock).
