Assessing the performance of Doho irrigation scheme by estimations of actual evapotranspiration obtained from satellite images
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The Doho Rice Irrigation Scheme in Butaleja District, Uganda, faces significant challenges, including poor watershed distribution and lack of water measuring systems, which could affect the achievements of the scheme against its planned objectives (Irrigation Performance). The traditional methods to assess Irrigation Performance are point based, expensive, and necessitate sophisticated instrumentation. This study aims at employing satellite data which has high spatial and temporal capabilities in assessing the performance of Doho Irrigation Scheme through estimations of Actual Evapotranspiration (ETa). ETa was calculated using the Surface Energy Balance System (SEBS) algorithm, GLDAS meteorological data, and Landsat 7 ETM+ satellite imagery on five clear days between January and April 2020. The SEBS ETa was validated using the in-situ (Advection-Aridity) ETa, which was calculated using weather data from two ground stations. SEBS performed well across both stations, with a Mean Absolute Error (MAE) of 0.47mmd-1, a coefficient of determination (R2) of 0.71 for station 1, and an MAE of 0.36mmd-1, an R2 of 0.68 for station 2. Using water balance metrics (Equity and Adequacy), the derived ETa was used to assess the Irrigation Performance of the scheme. The findings showed that, the spatial distribution of water (equity) was found to be generally fair, with a Coefficient of Variation (CV) ranging from 0.08 to 0.11 and slightly close to the 0.10 threshold. The mean value for the sufficiency of water use (adequacy) was 0.87, which was above the 0.65 threshold and indicated a reasonably adequate water supply throughout the scheme. The study highlights the growing gap between water demand and supply, providing a basis of relevant institutions investing proactively in the improvement and modernization of irrigation infrastructure. The study's findings could be used in future research and benchmarking with other Irrigation Schemes to address the country's water resource management challenges.