The irrational use of irrigation water resources is a major constraint to agricultural development in the watersheds of Morocco, including the Tadla sub-basin. It is essential for these areas to have effective instruments for managing and organizing the control and distribution of water resources and to ensure their protection and conservation. Within this context, this study focused on the Tadla sub-basin, where there has been a marked decrease in the supply of irrigation water. Using a dynamic agro-economic model called ‘TADMOD’ (for TADla Basin MODel), which classifies agricultural units according to their different sources of irrigation water, the study’s main purpose was to analyse the interannual variations in selected irrigation water management indicators. One of the most important indicators studied here was irrigation water shadow price between 2011 and 2020. The results of the analysis revealed important differences in this indicator value among the observed agricultural units. Its average value, calculated by TADMOD, was about 1.33 MAD4 (Moroccan Dirham) per cubic metre of water. The model showed that, over the ten simulated years, reduced water supplies in the Tadla sub-basin would lead to an increase of 33.2%, on average, in the irrigation water shadow price and to a decline in the cultivated area and total consumption of irrigation water. The reduction in the cultivated area would lead to a slight fall in valueadded, estimated at 3,180.78 million MAD per year in 2010-11, the first year of simulation.