Expose player to more stress and much more survival threats to increase fun

After a few droughts, the game becomes too easy. The game needs to throw many more survival threats at the player, to create an "air" of imminent extinction and demands that the player keeps constant attention. Compared to timeless Impressions Games classics like Caesar3 and Pharaoh, this game has very little stress. The game would be more fun with more stress.

All it takes is a large enough water reservoir (and tiered pumping), and around that continuous food/wood production and all threats to the colonies' survival are neutralized. This is true on all of the maps on hard difficulty, and the player quickly figures out how to beat the drought length build-up, up to the longest droughts.

Some ideas:
Unpreventable earthquakes.
Unpreventable lighting strikes, that cause a fire.
Landslides that destroy/bury buildings (preventable by trees).
Stormy weather, which effectively increases water from water sources (and requires the player to plan for storm drains).