Satellite and Model-Based Estimation of Crop Water Requirement of Major Irrigated Crops in the Koga Irrigation Scheme, Ethiopia
Abstract
An adequate supply of water and nutrients is vital in crop cultivation to conserve water, prevent water shortages, minimize production losses, and curb the excessive utilization of water resources. This study aimed to estimate the water demand of major irrigated crops using open-access portals and reanalysis datasets within the Koga irrigation scheme. We collected climate data from the local weather station, WaPOR, and ERA5-Land open-source datasets. The Koga Irrigation Development Office provided the field data for the entire irrigation system. The Modified Penman-Monteith equation was employed to compute the reference evapotranspiration. The single-crop coefficient approach was applied to determine crop evapotranspiration (ETC). The result indicated a strong correlation between the measured and predicted values. Additionally, it was also found that the ETC tended to peak during the mid-stage of the crops, and a robust relationship between the measured and estimated values was examined on a monthly scale. The seasonal average water requirements for wheat were 532, 510, and 542 mm, respectively, whereas maize had mean values of 603, 589, and 636 mm, respectively. Potato water needs averaged 549, 529, and 564 mm, and for tomatoes, the water requirements were 540, 532, and 583 mm, based on observed, satellite, and model-based estimations, respectively. Remarkably, the highest crop evapotranspiration (ETc) value was consistently obtained for maize crops for all estimation scenarios, suggesting that it has physiological traits that enable efficient water use, but also results in higher overall water consumption due to its rapid growth and large biomass in comparison to wheat, potato, and tomato. Our findings indicated that the model-based estimates exceeded the satellite-based estimates by 5.9 to 8.7% and surpassed the measured values by 1.9 to 7.4%. In conclusion, our research highlights the importance of utilizing satellite and model-based data to calculate crop evapotranspiration in irrigation schemes and benefits decision-makers, water managers, agronomists, stakeholders, and irrigation operators.