Bonedrought - abunchofhacks/epicinium-documentation GitHub Wiki
Each space can be affected by Bonedrought.
Bonedrought occurs on Desert tiles if at least 60% of the map is covered by Chaos. Bonedrought also occurs on City, Town, Farm, Outpost, Barracks, Industry, Airfield and Rubble tiles if at least 80% of the map is covered by Chaos.
If Bonedrought is present on a space, it lowers the hitpoints of tiles and ground units in that space by 1 (down to 1), making them more vulnerable to damage.