Investigations, carried out in the irrigated zone of Doukkala in western Morocco, allowed the evaluation of the inter-annual variability of ET0-P during the period 1992–2017 and compared its anomalies (i.e., deviations from average) with anomalies in annual water release. Overall, it appeared that anomalies in water release were consistent with anomalies in ET0-P. The actual evapotranspiration (ETa) was estimated using a time series of multi-spectral satellite image data by applying the Surface Energy Balance (SEBAL) algorithm in a dry (2015–2016), wet (2014–2015), and reference year (2013–2014). We have determined the quartiles of the distribution of the ET0-P time series, and the seasonal and annual anomalies in ET0-P, ETa and release water delivery (Wd ) were compared. In the period 1992–2017, the relative anomalies in ET0-P and Wd were similar only in 2000–2001 and 2015–2016. The analysis of anomalies in water inflow and stocks confirmed the response in increased Wd following wet years with higher inflow and replenishment of the reservoir.
The response of crop water use to the irrigation water supply is evaluated by comparing anomalies in the ratio of actual to maximum ET, i.e., ETa/ETc with anomalies in Wd. Overall, the study shows that Wd responds to inter-annual variability in the pre-irrigation season water inflows into the reservoirs, rather than in ET0-P. On the other hand, actual crop water use, i.e., ETa/ETc, does respond to inter- and intra-annual variability in Wd. This evidence suggests that there is scope for adaptive water management based on a flexible adaptation of water release to inter- and intra-annual variability in water demand.