Operational irrigation monitoring in data-scarce schemes using field observations, water accounting tool and remote sensing in Northern Ghana

Irrigation is a major source of freshwater pressure in semi-arid regions and is increasingly constrained by water scarcity, operational inefficiencies, and user conflicts. Yet routine monitoring of irrigation withdrawals, conveyance losses, and field-level water use remains limited due to weak measurement infrastructure. This study demonstrates an integrated methodology of field observation of irrigation water use and efficiency,  water accounting tool validated with field observation, and a remote sensing products  to quantify irrigation performance, specifically efficiency, adequacy, and equity, in a reservoir-fed irrigation scheme in northern Ghana under a unimodal rainfall regime. During the 2025 dry season, monitoring combined daily water-level observations from standardized flow structures in the main canals, selected laterals and application of water on selected fields. Flow rates were estimated based on hydraulic empirical equations and Manning-hydraulic equations for defined concrete channels. Measurements covered upstream, midstream, downstream sections of both main canals and selected laterals. Results reveal strong spatial degradation of water delivery. In the main canals, average discharge declined from 1.80 to 1.20 m³ s⁻¹ (right canal) and 2.17 to 0.85 m³ s⁻¹ (left canal), corresponding to conveyance efficiencies of 87.1% and 83.8%, respectively. At lateral scale, losses were substantially higher, with efficiencies dropping to 78.4% in one lateral and 58.5% in another, reflecting seepage, overflow, sedimentation, and structural constraints. Application irrigation depths in selected fields varied widely (21–32 mm versus 29–77 mm), producing application efficiencies of 31% and 62%, and indicating inequities in delivery reliability and water access. Unregulated abstractions (pump and tanker withdrawals) were estimated at ~38,000–53,000 m³ over the monitoring period, contributing to instability during peak demand. Independent 30-m remote-sensing evapotranspiration (ETa) captured irrigation signals and enabled scheme-wide diagnostics that complement discharge monitoring. Relative ETa provided a proxy for adequacy across water user associations and irrigation blocks, while ETa variability highlighted inequitable allocation and inconsistent delivery. Combined indicators support actionable options, including prioritizing rehabilitation in high-loss reaches, improving rotational delivery to tail-end blocks, targeting enforcement in abstraction hotspots, and benchmarking performance across associations for adaptive irrigation management. This is done in collaboration with the Ghana Irrigation Development Authority to validate the results and create ownership of the results for decision-making for expanding the irrigation area and improving the scheme's efficiency.