Here's what someone on the Mule boards says, based on decompiled code from the original game:
These are events which occur either just before or just after the Production phase (splat splat splat splat splat...)
For the first 11 rounds of the game, a random event is chosen from a collection of 20. Certain events have a greater chance of occurring than others, and once it has occurred once, it is less likely to happen in the future. The best of way of visualizing this is as a deck of 20 cards, which is shuffled at the beginning of the game and then dealt out, 1 card per turn:
Event Max Occurrences Description
Pest Attack 3 Random food plot of the player in 1st or 2nd place loses all its production.
Pirate Ship 2 All Crystite is removed from Store and player storage/production
Acid Rain Storm 3 Storm passes through a random row. Food MULEs in the row produce 4 more, Energy MULEs produce 2 less. All other rows produce +1 Food and -1 Energy.
Planetquake 3 All Smithore/Crystite MULEs lose half their production.*
Sunspot Activity 3 All Energy MULEs produce +3 Energy (max of Cool.
Meteorite Strike 2 A meteorite strikes a random plot (other than the Store or the river valley) that does not already have a 3-Crystite deposit, turning it into a 4-Crystite deposit and destroying the MULE there, along with its production.
Radiation 2 A random plot belonging to the 1st or 2nd place player loses its MULE.
Fire in Store 2 All goods in Store are removed
Note that in this version, the pirates steal smithore too, though I believe this will be reverted in the next version.
