The agricultural sector accounts for the majority of global freshwater use, particularly in the semi-arid regions of the southern Mediterranean, where water demand is especially high. This intense consumption directly contributes to the depletion of groundwater resources, making the rational management of irrigation water imperative. In this context, accurate monitoring of vegetation water status is essential for optimizing irrigation practices. Radar data are directly sensitive to soil and vegetation water status due to their dependence on the dielectric properties of both. Several previous studies on forests and annual crops have demonstrated their sensitivity to vegetation water dynamics. The objective of this study is to analyze the diurnal variations in the C-band radar backscatter coefficient (σ⁰) over an olive orchard in a semi-arid region. To this end, an in situ tower-based radar system was installed in 2020 in the Chichaoua region, in the Haouz plain of Morocco. The radar antennas were directed toward an olive orchard, and the system collected C-band radar data in VV, HH, and VH polarizations at 15-minute intervals. In parallel, measurements of evapotranspiration, sap flow, surface soil moisture, and root zone moisture were collected every 30 minutes. The results show that σ⁰ exhibits a pronounced diurnal cycle in all three polarizations, with lower values during the night and higher values throughout the day. The increase in σ⁰, observed at sunrise, coincides with the onset of evapotranspiration and sap flow. It then continues to rise, reaching its maximum in the early afternoon, before gradually decreasing and stabilizing at night. These diurnal cycles of σ⁰ are in phase with those of evapotranspiration and sap flow, highlighting the sensitivity of C-band σ⁰ to the diurnal variations in the water status of olive trees. These findings demonstrate the potential of sub-daily C-band radar data for monitoring the water status of vegetation, and thus their possible use for the early detection of water stress.