3.3.1. Impact of Future Climate Change on Durum Wheat Grain Yield

With the aim of showing the projected impacts of changes in TS, PS, and the atmospheric CO2 concentration, on rainfed durum wheat grain yields, the charts in Figure 4

were carried out. So, for the BP, as shown in Figure 4a,b, the average grain yield of Mexicali cultivar simulated by AquaCrop crop model are estimated to 34.7 and 23.3 qha−1 at Setif and BBA experimental sites, respectively. So, a Mexicali cultivar grain yields enhancements estimated at (+82 and +76.6) and (+16 and +133%) are projected under the Sc1 and Sc2 scenarios, in Setif and BBA field tests, respectively.

**Figure 4.** (**a**,**b**) Impact of future change in seasonal temperatures, precipitations, and CO2 concentrations on Mexicali cultivar grain yield at BBA and Setif sites.

3.3.2. Wheat Growing Season Length, Reference Evapotranspiration and Water Productivity Prediction under Future Climate Change Scenarios

Figure 5 summarizes the results of AquaCrop simulations of the thirty years averages of GSL, WP, and ET0, under the BP, Sc1, and Sc2 scenarios at BBA and Setif experimental sites. Figure 5 also shows the relationship between GSL, WP, and ET0 variations with the changes in seasonal temperatures and CO2 concentrations projected under Sc1 and Sc2 with respect to their averages simulated for the BP.

**Figure 5.** (**a**,**b**) Impact of temperature and CO2 concentrations futures changes on reference evapotranspiration and wheat water productivity and the growing cycle length.

As indicated in Figure 5a,b, the Mexicali cultivar's GSL follows an inverse evolution of TS one under Sc1 and Sc2 scenarios at BBA and Setif sites, respectively. For the BP, AquaCrop simulated a Mexicali cultivar's GSL of 161 and 151 days at Setif and BBA sites, respectively. It is predicted that a shortening of the Mexicali cultivar's GSL by 30 and 47 days occurs in Sc1; meanwhile, the Mexicali cultivar's GSL lengthening of +10 and +13 days are predicted under the Sc2 conditions at Setif and BBA sites, respectively. In comparison with the BP, the shortening of the Mexicali cultivar's GSL under Sc1 by 30 and 47 days under Sc1 is due to the increase in TS of +3.5 and +4.5 ◦C at Setif and BBA sites, respectively. However, the Mexicali cultivar's GSL lengthening by 10 and 13 days in Sc2 is due to the drop in TS of −0.3 and −0.1 ◦C at Setif and BBA sites, respectively.

In addition to these above results, the Pearson correlation test revealed the existence of a negative and statistically significant correlation between this Mexicali cultivar's GSL and TS during the BP, under both Sc1 and Sc2. However, this test proved that there is a positive and statistically significant correlation between the Mexicali cultivar's GSL and PS during the BP and under both Sc1 and Sc2 scenarios at theSetif and BBA sites. Thus, the lengthening of the Mexicali cultivar's GSL by 10 days under Sc2 at the Setif site could alsobe explained by the PS increase by +65.6 mm. So, despite the shortening of Mexicali cultivar's GSL by the effect of the expected TS increase, Mexicali cultivar's grain yield is projected to be enhanced under Sc1.

Moreover, according to the results of this study reported in Figure 5a,b, the AquaCrop model simulated thirty years average water productivity (WP) of 1 and 0.7 kgm−3 of the Mexicali cultivar for the BP at the experimental sites of Setif and BBA, respectively. Thus, this crop model predicted WP enhance, estimated at (+1 and +0.3) and (+0.6 and +0.9) kgm−3, corresponding to WP enhancement rate of (+100 and +43) and (+60 and +129)% under Sc1 and Sc2, at Setif and BBA experimental sites, respectively.

Furthermore, according to Figure 5a,b, the ET0 simulated by the AquaCrop crop model for the BP is estimated to be 562.5 and 542.8 mm, for the Setif and BBA sites, respectively. Thus the drops of (−118 and −58.6) and (−32 and −47) mm, corresponding to decline rates of (−21 and −11) and (−6 and −8)%, are projected under the Sc1 and Sc2, at the Setif and BBA sites, respectively. So, these above ET0 declines projected under Sc1 could be induced by the shortening of MC's GSL. However, under Sc2, the lengthening of the Mexicali cultivar's GSL did not prevent the ET0 decline.