Stochastic Optimisation of Irrigation Water Allocation Under Uncertainty in Multi-User River Basins in Nigeria

This study develops and applies a stochastic optimisation framework for irrigation water allocation under uncertainty in multi-user Nigerian river basins, advancing the theoretical and methodological foundations for equitable and efficient water resource management. Nigerian river basins including the Hadejia-Jama'are, Benue, and Niger River systems host multiple competing water users across irrigation schemes, municipal water supply, hydropower generation, and environmental flow requirements. Current water allocation practices rely on deterministic fixed allocation schedules that do not account for hydrological variability, demand uncertainty, or climate change, resulting in suboptimal water use and frequent allocation conflicts. This study develops a two-stage stochastic programming model for optimal water allocation that explicitly accounts for hydrological uncertainty through probability-weighted scenario trees derived from observed flow variability and downscaled climate projections. The model is applied to the Hadejia-Jama'are basin, incorporating water demand data from 12 irrigation schemes, municipal water supply systems, and hydropower facilities from field surveys and River Basin Development Authority records. Multi-objective optimisation balances aggregate economic benefit, equity of allocation across water user groups, and reliability of meeting minimum allocation commitments. Stochastic programming solutions are compared against deterministic benchmark allocations. Findings reveal that stochastic optimisation improves aggregate basin economic benefit by 18 percent and reduces allocation shortfall frequency by 34 percent compared to deterministic schedules, while maintaining comparable equity outcomes. The study contributes an original stochastic allocation framework for Nigerian river basins and recommends its adoption in Basin Development Authority planning procedures.

Keywords: stochastic optimisation, irrigation water allocation, river basin management, Nigeria, water resource engineering.