Floodplain Farming Expansion

Centered around floodplains, this mod introduces a new mechanic emphasizing sustained cultivation. "Floodplain Degradation" is triggered either periodically or when an era changes. If a floodplain is re-improved between two degradation events, it gains stackable output bonuses. However, if two degradation events occur consecutively without re-improvement, the floodplain turns into a swamp and loses all accumulated bonuses. Clearing the swamp will restore the tile to a floodplain. Under the effects of this mod, floodplains become the feature with the highest development potential, serving as the core economic zone of your empire. The inspiration comes from the agricultural environment of the Fertile Crescent, where irrigated fields, saline-alkali lands, and swamps intermingle. This mechanic abstracts the long-term historical accumulation of irrigation infrastructure, land maintenance, and farming expertise in mature agricultural regions into the repeated improvement of tiles. This represents how long-term cultivation gradually creates highly productive farmland, while land degradation occurs due to abandonment, war damage, and similar factors. Main Features: "Floodplain Degradation": Triggered periodically (e.g., every 24 turns) or when the era changes. Upon triggering: All improved floodplain tiles within a civilization’s territory have a chance (e.g., 50%) to lose their improvements. Re-improving such tiles grants a random bonus of +2 Food or +2 Production. This bonus is stackable (default maximum: 5 stacks), and only takes effect when the tile has an improvement. All unimproved floodplain tiles within a civilization’s territory—those without improvements or districts—have a chance (e.g., 50%) to transform into swamps, losing any previously accumulated output bonuses. When a swamp is cleared, the tile’s terrain is converted into a floodplain corresponding to the local base terrain (e.g., Desert Floodplain, Grassland Floodplain, etc.). After a "Floodplain Degradatio