El Nino-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 Ni & ntilde;o-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 Ni & ntilde;o increases solar irradiance and suppresses cotton returns, reducing median Levelised Cost of Hydrogen (LCOH) to 4.99 USD kg(-)& sup1; and system breakeven price to similar to 4.7 USD kg(-)& sup1;. La Ni & ntilde;a suppresses irradiance and elevates cotton profitability, increasing LCOH to 7.08 USD kg(-)& sup1; and raising agricultural water value by 25-40%. At 5.5 USD kg(-)& sup1; hydrogen price, reallocating 1% of irrigation water gains total system value by similar to 6600 USD under El Ni & ntilde;o but loses similar to 26,000 USD under La Ni & ntilde;a. A 10 MW green H2 facility employing LT-MED is assumed to require similar to 13 L net make-up H2O kg(-)& sup1; H-2, 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.