Water
Parameters
Annual extractable per tile
180000
Liters of groundwater the aquifer below one tile (20m × 20m = 400 m²) can yield per year. Multiplied by the map’s bounding-box tile count at city creation to produce the city-wide annual extraction cap, which is then frozen into the GROUNDWATER_BUDGET meta so existing saves keep playing under whatever rules were in force when they were generated. Calibration: USGS aquifer recharge across the conterminous US ranges from <10 mm/yr (desert SW) to 1,200 mm/yr (Pacific NW), with mid-latitude balanced regions in the 150-300 mm/yr band; the Mediterranean Province-of-Alicante estimate is ~69 mm/yr. Pure-precipitation recharge at 150 mm/yr over 400 m² gives 60,000 L/yr/tile, but real cities also draw on lateral inflow and deeper aquifer storage built up over centuries. We use 180,000 L/yr/tile (≈450 mm/yr effective inflow, in-range for humid-temperate US) tuned so the three current scenarios land on a power-of-two tower cadence at the current 500,000 L/day per-tower draw: classic 64×64 → 4 towers, large 128×128 → 16 towers, river 128×128 → 32 towers (with the 2× river multiplier).
River scenario multiplier
2
Bonus multiplier applied to the city-wide groundwater cap when the map is the river scenario (Velaria). A surface river continuously recharges the alluvial aquifer beneath the city via streambed leakage and bank infiltration — the river-to-aquifer flux can easily double the effective annual yield versus the same land area with no river. 2× is a deliberately gamey round number rather than a calibrated coefficient: river recharge in real catchments ranges from 30% to several hundred percent of land-based recharge depending on geology and stream geometry (USGS, Streamflow and the Hydrologic Cycle). Classic and large scenarios use a 1× multiplier (no bonus).
Source: USGS — Streamflow and the Hydrologic Cycle (river-aquifer exchange)