A safe and just operating space for water at municipal scale: population, agriculture and mining in Chihuahua, Mexico, to 2050

Katya Perez-Guzman , Isabel Rodriguez Peña

Water allocation decisions in Mexico are taken municipality by municipality, yet water scarcity is assessed at national or basin scale. We operationalize a safe and just operating space for water for each of the 67 municipalities of Chihuahua, Mexico's largest and driest mining state, with both bounds drawn from national law rather than imposed by the analyst: an ecological ceiling equal to the renewable availability published by the federal water authority, and a social floor equal to the domestic water quantity that Mexican courts are now making enforceable. Between them lies the space legitimately available to agriculture and mining. We couple official data on population, irrigated agriculture and metal mining in an open, formula-transparent spreadsheet calculator, and run every combination of demographic (SSP), mineral-demand (IEA), water-intensity, climate-elasticity and social-floor assumptions — 324 scenario combinations to 2050. Three findings are robust across the entire scenario space. First, overdraft is structural, not scenario-dependent: 15 municipalities, concentrated in the irrigated districts of the Conchos basin, exceed their development space in every combination, by 1,205–1,388 hm³ per year in aggregate. Second, mining never exceeds 0.3% of state water use, but reaches 36–78% of municipal use in Sierra Tarahumara municipalities that lie in a ~45,000 km² area for which no aquifer has ever been delimited — where the administrative instrument the law requires does not exist. Third, for the state capital and Ciudad Juárez, the choice of the legal minimum vital (50, 100 or 150 L per person per day) — not climate or mining — decides whether any development space remains. The calculator runs in Excel or LibreOffice with visible formulas and is released with the paper.