Abdellah Oumou

The Saiss plain in northern Morocco covers an area of 2300 km² and is one of the main agricultural contributors to the national economy. However, climate change and water scarcity reduce the region’s agricultural yields. Conventional methods of estimating evapotranspiration (ET) provide localized results but cannot capture regional-scale variations. This study aims to estimate the spatiotemporal evolution of daily crop ET (olives, fruit trees, cereals, and vegetables) across the Saiss plain. The METRIC model was adapted for the region using Landsat 8 data and was calibrated and validated using in situ flux tower measurements. The methodology employed an energy balance approach to calculate ET as a residual of net radiation, soil heat flux, and sensible heat flux by using hot and cold pixels for calibration. METRIC-ET ranged from 0.1 to 11 mm/day, demonstrating strong agreement with reference ET (R² = 0.76, RMSE = 1, MAE = 0.78) and outperforming MODIS-ET in accuracy and spatial resolution. Olives and fruit trees showed higher ET values compared to vegetables and cereals. The results indicated a significant impact of ET on water availability, with spatiotemporal patterns being influenced by vegetation cover, climate, and water resources. This study could support the development of adaptive agricultural strategies.

In areas highly affected by drought in a changing climate, evapotranspiration (ET) becomes a significant parameter affecting soils and vegetation. ET estimation on a large scale remains a problem in understanding the hydrologic system; it is complicated over heterogeneous land use and land cover. However, the availability of remote sensing imagery and local weather data has made ET mapping possible through the application of models. In this study, the METRIC model was applied using Landsat satellite imagery and climatic data. This involves resolving the surface energy balance equation by calculating net radiation, soil heat flux, and sensible heat flux. Two satellite images were used at a resolution of 15m: one for January as a wet season and another for July as a dry period. ET ranges between 2 and 12 mm/day. Higher values are estimated during the dry period, and lower values are attributed to the wet period. Furthermore, water bodies and vegetation are characterized by significant ET compared to bare soils and urbanized areas. The comparison of METRIC ET and reference ET showed a strong correlation with an R², RMSE, and MAE of 0.68, 1.0, and 0.78, respectively. This study can assist managers in their water and agricultural adaptation strategies against climate change.