In semi-arid and arid regions, crops face elevated atmospheric demands and endure prolonged periods of moderate to severe water scarcity. In this context, this study investigated the effectiveness of the photochemical reflectance index (PRI) and a normalized surface temperature index (T-norm) for proxy detection of the water stress of winter wheat crops. Furthermore, the potential of PRI for characterizing water, atmospheric or photo-inhibition stress, and wheat transpiration was assessed over experimental drip-irrigated crop fields in the Haouz plain, central Morocco. In practice, PRI observations were compared to agro-environmental variables such as Leaf Area Index (LAI), Available Water Content (AWC) at a root zone depth, net Radiation (R-n), Vapor Pressure Deficit (VPD) and the wheat transpiration derived from sap flows, lysimeters and a crop water balance model. Due to the strong relationship between PRI and LAI (R-2 = 0.91), another index named PRIj was derived to correct for this effect. The PRIj was found to be independent of structural effects related to LAI and significantly correlated with AWC (R-2 = 0.85). Using the PRIj index, we can reflect the level of water stress experienced by the wheat field throughout the experiment with an R-2 of 0.69 for a FAO-56 water stress coefficient (K-s) of less than 1. Under dry conditions, for an AWC below 30%, the correlation between AWC and T-norm gives an R-2 of 0.29. However, comparison of PRIj with the T-norm index showed that PRIj is an early water stress index and provides information on the state of the vegetation cover at all stages of wheat development. The study's findings can have a significant impact on the use of the PRI as a water stress indicator, helping in the optimal irrigation of crops.