estimating water productivity of center-pivot irrigation systems using the wapor (case study: moghan plain)

Water productivity is essential for sustainable agriculture, especially in semi-arid regions with limited water resources. in the moghan plain during 2020–2024, this study evaluates net biomass water productivity (nbwp) and gross biomass water productivity (gbwp) in three agricultural fields (p, q, and r) cultivating silage maize under center pivot irrigation from 2020 to 2024. ground measurements of irrigation depth, crop yield, and evapotranspiration, combined with temperature and precipitation data, were analyzed to understand temporal variations and the impact of environmental and management factors. results showed that nbwp increased from 2.42 to 3.03 kg/m³ in field p, 2.40 to 3.33 kg/m³ in field q, and 2.12 to 3.56 kg/m³ in field r, with field q achieving the highest gain (39%). gbwp fluctuated more significantly, ranging from 1.5 to 2.63 kg/m³, with the lowest values in 2021 corresponding to drought conditions and high temperatures. comparison between field data and wapor satellite-based estimates revealed systematic underestimation by the portal, with gbwp and nbwp values underestimated by 40–50%, mainly due to differences in spatial resolution, input data quality, and algorithmic assumptions for evapotranspiration estimation, as well as its inability to capture localized agronomic practices such as crop rotation and irrigation scheduling. the study also identified uniform irrigation rates applied throughout the crop cycle, ignoring the dynamic water demands during different growth stages. this led to over-irrigation during maturity and under-irrigation during critical reproductive phases, exacerbating water stress under high temperatures. the findings emphasize the necessity of integrating precise field measurements with remote sensing data for accurate water productivity assessment. implementing stage-specific irrigation management can optimize water use efficiency and maintain crop biomass production under varying climatic conditions. this research provides valuable insights for improving irrigation strategies and water resource management, contributing to agricultural resilience in water-scarce semi-arid environments facing climate variability.