Evaluation of the performance of ergani dam irrigation system by remote sensing techniques using high resolution satellite images

Management of water resources is a major factor for a sustainable agriculture. In addition, the main parameter that should be known for the effective use of water resources is evapotranspiration (ET). ET can be determined simple or complex methods for just a location. However, it is possible to estimate quickly, economically and objectively with technological tools and new techniques in case that the large areas are considered. In this context, there are many methods for ET mapping. The use of these methods, which are based on remote sensing (RS) techniques, can play an active role in determining the available regional and project-based irrigation performance. In this study, actual ET (ETa) maps were created by METRIC model, based on energy balance and considered at high resolution internalized calibration, with using high-resolution Landsat images of the irrigation seasons (April-October) of 2023-2024 for the Ergani Dam Irrigation System, Diyarbakır. In addition, crop ET (ETc) was calculated using the reference ET (ETo) and current vegetation coefficient (Kc) values obtained from the climate data of the study area. The performance of the Ergani Dam Irrigation System was determined using ETa and ETc. Also, Kc values of major crop pattern were also re-estimated by RS techniques. In the study, the performance of the irrigation system was evaluated according to the indicators of relative water supply (RWS), relative irrigation water supply (RIS), overall consumed ratio (ep), depleted fraction (DF), crop water deficit (CWD), relative ET (RET) and relative rainfall supply (RRS) related to ET. As a result of the study, monthly and seasonal values for the years 2023 and 2024, respectively, it was calculated as for RWS are between 0.62-2.27 and 1.02, between 0.99-1.44 and 1.10; for RIS are between 0.61-3.31 and 1.01, between 0.99-2.30 and 1.10; for ep are between 0.30-1.65 and 0.99, between 0.44-1.01 and 0.91; for DF are between 0.81-2.29 and 1.09, between 0.68-1.16 and 0.93; for CWD are between 0.00-22.17 mm and 22.17 mm, between 0.00-39.66 mm and 52.66 mm; for RET are between 0.93-2.15 and 1.10, between 0.87-1.30 and 1.02; for RRS are between 0.00-0.59 and 0.05, between 0.53-0.73 and 0.08. When the study results were evaluated seasonally, although the performance indicators indicated sufficient water supply, it was determined that there were significant differences on a monthly basis. Therefore, it can be said that monthly evaluations are more accurate than seasonal analyses in irrigation management. Within the scope of RS-based estimation of Kc values, it was determined that Normalized Difference Vegetation Index (NDVI) images were in high accordance with Kc values considering water stress. In general, it has been determined that irrigation practices carried out under farmer control are not effective in terms of quantity and timing, especially in dry months such as June, July and August. However, in other months, water conservation is recommended in order to increase the efficiency of irrigation water use. As a result, it was concluded that farmers should be made aware of the amount of irrigation water and the timing of irrigation in order to increase irrigation performance