Food security in the world that water shortages are faced is very important, especially in arid regions. Effects of climate change on agricultural water requirement have doubled this importance. In this study, the risk of water demand has been assessed for a wide range of products under climate change. AOGCM models have been used to simulate climate variables. The climate change scenarios of climatic variables were weighted by mean observed temperatures and precipitation method and their probability distribution functions were produced. Using the Monte Carlo method, 200 samples (discrete values) of the probability distribution function of the monthly climatic variables downscaled for each month were extracted by SIMLAB and finally time series of climatic variables has been produced in future. Potential evapotranspiration in the future through the relationship of temperature and potential evapotranspiration in the base period was calculated. With introducing about 200-monthly time series of climatic variables in future period to model, water requirement and changes in crops water demand volume were investigated. Investigations indicate water demand volume for crops based on current area under cultivation will increase between 0.05 to 0.96 (106 m3/yr) for risk of 25%, between 0.04 to 6.87 (106 m3/yr) for risk of 50%, and between 1.16 to 12.68 (106 m3/yr) for risk of 75%. Therefore, the results indicate that risk of water requirements will increase. The volume of water demand will be about 2.5, 16 and 31 (106 m3/yr) with risk of 25, 50 and 75 percent, respectively.