Climate context of the watershed

Annual precipitation

Precipitation decreases towards the SE where the station of Anoceur is located. It has an average of 504 mm, lower than that of Sefrou (517.2 mm), and that of Allal El Fassi dam (335.3 mm). This can be explained by the orographic effect of the sequences of high ridges. The annual average is 361 mm in Azzaba, 396.2 mm in Fez, 407.4 mm in Ain Timedrine. Thus, from the results obtained for the 5 stations, it can be deduced that the average rainfall for the sector studied is 417.8 mm, for the period between 1957/58 and 2009/10.

Average monthly precipitation

In the Sefrou watershed, there was a maximum average monthly rain (figure 4) of 54.92 mm in December, which makes this month the wettest of all the stations, while July is the driest. with an average rain of 3.86 mm, this will directly influence the runoff flows.

Assessment of the blade of water fallen on the watershed

The fallen layer of water can be estimated by several methods, making it possible to integrate into point data relating to the different stations, a surface result, which makes it possible to estimate spatial precipitation. ‘Thiessen polygon’ is the applied methodology, as a statistical method, which amounts to carrying out the weighted average of the precipitation measured in the rainfall stations of the watershed. The influence area of each station measurement “called the Thiessen polygon” is the weighting factor. These polygons are obtained graphically (figure 5), by plotting the perpendicular bisectors of the segments connecting two neighboring rainfall stations, on a geographic or topographic map.

Isohyet method

To make interpretation of precipitation easier, the map of isohyets shows that there is a progressive precipitation gradient between the different stations. From this figure, we notice that the rainfall gradient increases from North to South in the direction of high altitudes (figure 6).
Thus, precipitation becomes significant at the stations located at high altitudes. We note that some summer months are characterized by the predominance of rain mainly linked to the frequency of local thunderstorms. These are due to the strong insolation on the ground which sometimes gives rise to updrafts which causes the formation of stormy precipitation.

Estimated mean of the water slide calculated by the three methods

In order to reconcile between the three different values found by each method (table 1), and to quantify the volume of the blade of water fallen on the basin, it is recommended to calculate an average between them. Annual volume of precipitated water (in m3), for the Sefrou watershed, can be estimated as follows:
V = 183, 96\(.10^{6}m^{3}\)/year

Evaporation, Evapotranspiration and flow deficit

Real Evapotranspiration (ETR)

Actual evapotranspiration (ETR) is the sum of the quantities of water evaporated by the soil and by plants when the soil is at its current specific humidity and the plants at a stage of real physiological and sanitary development under real conditions and taking into account the water available.
It turns out that the actual evapotranspiration is very important, it is calculated from the average of the three methods (Thornthwaite, 1948; Coutagne,1954; Turc, 1955) is 389.22 mm for the entire watershed, whose annual average precipitation represents a value of 454.22mm. The percentage of loss represents 85.69% of inflows from the water system having a volume close to 161.28 million m3, while the rest will represent the volume of water drained and the amount of underground infiltration, the latter reaching 14, 31% with a value of 22.68 million m3 /year.