The Tassaout watershed (upstream Moulay Youssef dam) belongs to a semi-arid climatic context, characterized by limited precipitation. In addition to the scarcity and uneven distribution of water resources, under the shadow of current climate change, the region is subject to increasing demand for water resources. Low water is a seasonal event that can recur every year. Annual variations in precipitation can impact the severity of low water. This article attempts to contribute to the study of the severity and seasonality of low water levels based on the water deficit recorded during these periods. For this, we used the SPA (Sequent Peak Algorithm) method based on the amount of water deficit. The threshold for the appearance of low water was determined from the Q75 indicator extracted from the classified flow curve based on the daily flow data measured at the two stations; of Ait Tamlil and Tamsemat, which covers the period from 1978 to 2016.

In a context of climate change with a growing population, the pressure on water resources is increasing. In Morocco, water resources are scarce and poorly distributed in time and space. To face this situation, the state has established strategies and laws since the 1960s, but they have not considered the management of low-flow situations. The management of such situations is a major pillar for an integrated and sustainable management of the water resource. The present article aims at identifying the daily low-flow rates (VCNd) in a semi-arid climatic context, that of the watershed of the river Srou, first tributary of the river Oum Er Rbia in the central Middle Atlas. The data used concern the daily flows of the upstream station of the watershed (downstream Elhri) and the downstream station (Chacha N’mallah) for the 1976-2016 period. The results obtained show that the daily low-flow rates on an annual scale are very stable between the different durations. On the other hand, they show a strong variability on an interannual and spatial scale. Low flows occur throughout the watershed between July and September. Severe low-flow situations occurred in 1995 and 2008.