Multi-scale assessment of irrigation water use and supply in the Amibara Irrigation Scheme, Ethiopia using Landsat-derived evapotranspiration and field data

Accurate estimation of irrigation water use and supply is essential for effective irrigation management, yet irrigation withdrawals remain largely unmetered and unreported in many schemes. This study applied a remote sensing–based approach to quantify irrigation water use and supply in the Amibara Irrigation Scheme, Ethiopia. The irrigation component of crop evapotranspiration (Blue ET) was partitioned from a high-resolution Landsat-based ETa product using the Water Accounting Plus (WA+) framework. Blue ET estimates were then integrated with irrigation efficiency parameters to derive remote sensing–based irrigation supply (RbIS) at block, canal and scheme scales. Crop type maps for 2010 and 2024 and a digitized irrigation layout provided the spatial basis for assessing irrigation performance using relative evapotranspiration (RET) and relative irrigation supply (RIS) metrics. Crop mapping revealed a substantial decline in the gravity-fed irrigated area from 9941 ha in 2010 to 4532 ha in 2024. RbIS showed reasonable agreement with reported irrigation supply in 2010 (R² = 0.58) and measured supply in 2024 (R² = 0.77), although supply was consistently underestimated. The extent of irrigation water deficits increased between 2010 and 2024, with the proportion of cotton blocks experiencing water deficits rising from 40% to 67%. Key informant interviews and focus group discussions corroborated the observed irrigation water deficits in 2024, supporting the remote sensing–based assessment. Moreover, RET and RIS revealed spatial variability in irrigation performance across irrigation canals, suggesting potential under and over-supply of irrigation. Overall, the proposed approach provides a scalable framework for assessing irrigation water use and supply in data-scarce irrigation schemes.