We measured data from a field experiment at Maryout, Egypt, during 1991-92, 1992-93 and 1993-94 growing seasons to evaluate the productivity of some bread wheat varieties under rainfed and supplementary irrigation conditions at different growth stages. The experiment included twenty-four treatments, with four supplementary irrigation schedules: Only rainfed (170 mm); one irrigation at heading stage 480 m3 per ha; one irrigation at milk ripe stage 480 m3 per ha; and two irrigations at the above stages 960 m3 per ha, and six wheat varieties. Predicted and measured grain were compared and the results indicated that there were significant and favorable differences among the cultivars. There was a significant increase in the grain yield with increasing supplementary irrigation times. The potential impact of climatic change on wheat production was evaluated simulating wheat production under climatic change conditions by the year 2040 compared to the predicted production under current conditions. Results indicated that the grain yield increased differently according to the wheat cultivar. This may be due to the positive effect of duplication in CO2 on wheat as C3 plants.