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Study region: The study was conducted in the Chichaoua agricultural province in south-central Morocco, a semi-arid study area located on the western foothills of the High Atlas Mountains. This region is characterized by strong hydroclimatic constraints where irrigated agriculture relies heavily on groundwater resources and localized irrigation systems. Study focus: In semi-arid environments, reference evapotranspiration (ET₀) plays a central role in determining agricultural water demand and irrigation planning. This study investigates the spatio-temporal variability and long-term trends of ET₀ in the Chichaoua agricultural province over a 45-year period using gridded climate data from the ERA5-Land reanalysis combined with a satellite-based precipitation product. Reference evapotranspiration was estimated using the FAO-56 Penman-Monteith formulation and evaluated against operational ET₀ values derived from technical irrigation studies used for drip irrigation system design, in order to assess seasonal consistency and realistic orders of magnitude within an irrigation management context. The influence of meteorological drivers was analyzed using a combined framework including linear correlation, mutual information, and permutation-based Random Forest importance analysis, while long-term trends were assessed using nonparametric Mann–Kendall tests and Sen’s slope estimators. New hydrological insights for the region: Results indicate that ET₀ variability in the study area is primarily controlled by radiative and thermal factors, particularly solar radiation and air temperature, with secondary contributions from vapor pressure deficit and wind speed. Spatial patterns reveal a pronounced altitudinal gradient across the province, with mean annual ET₀ ranging from approximately 4.0–4.8 mm·day⁻¹ and seasonal maximum values approaching 6.8 mm·day⁻¹ in low-altitude agricultural zones. Beyond documenting climatic trends, this study provides an operational perspective by explicitly linking ET₀ variability to irrigation design practices used in drip irrigation projects. By relying on technical calculation notes from irrigated agricultural fields, the study demonstrates how changes in atmospheric evaporative demand are directly embedded in current irrigation system sizing assumptions. This approach bridges climate analysis and irrigation engineering and provides a transferable framework for interpreting ET₀ trends in terms of irrigation demand and supporting adaptive water management in semi-arid agricultural regions.
Bounajra et al. (Thu,) studied this question.