El Niño–southern oscillation effect on water allocation for green hydrogen and cotton irrigation in the Murray-Darling Basin

Freshwater scarcity is the principal barrier to inland green hydrogen, particularly where hydrogen competes with irrigated agriculture for regulated water supplies. This study quantifies how the El Niño–Southern Oscillation (ENSO) alters the relative water value of hydrogen and cotton in the Gwydir catchment of the Murray–Darling Basin. An integrated framework couples ENSO-conditioned climatic ensembles with a Monte Carlo techno-economic model linking solar PV generation, low-temperature multi-effect distillation (LT-MED), and alkaline electrolysis, alongside a cotton profit model and the Basin's water-rights system. The framework evaluates two water-procurement pathways: temporary allocation trades and permanent entitlements. ENSO strongly alters outcomes under both mechanisms. El Niño increases solar irradiance and suppresses cotton returns, reducing median Levelised Cost of Hydrogen (LCOH) to 4.99 USD kg⁻¹ and system breakeven price to ∼4.7 USD kg⁻¹. La Niña suppresses irradiance and elevates cotton profitability, increasing LCOH to 7.08 USD kg⁻¹ and raising agricultural water value by 25–40%. At 5.5 USD kg⁻¹ hydrogen price, reallocating 1% of irrigation water gains total system value by ∼6600 USD under El Niño but loses ∼26,000 USD under La Niña. A 10 MW green H2 facility employing LT-MED is assumed to require ∼13 L net make-up H2O kg⁻¹ H₂, equivalent < 0.1% of cotton irrigation water use in the Gwydir catchment. In this context, green hydrogen represents a potential low-carbon substitute for fossil fuels used in inland agricultural regions. Findings demonstrate that inland hydrogen feasibility is governed by climate-conditioned economic scarcity within the regulated water-rights system, rather than physical water availability.