This research paper intends to identify the effect of CO2 and atmospheric temperature on yield and water use efficiency of rice crop. Rice is one of the largely cultivated crops of the SW plains of Uttarakhand. It is important to know the effect of changing climate on rice. Therefore 10 rice cultivars (IR 20, IR 36, Jaya, Malviya-36, NDR-359, NDR-97, Pant-10, Pant-4, PR114 and Sarjoo-52) were used for the study. The model results showed that the yields and WUE of all the varieties increased significantly under elevated CO2 concentrations and decreased significantly with increasing temperatures. Under elevated CO2 scenario NDR97 has more capability to utilize higher CO2 in producing more carbohydrates with higher WUE and thereby resulting in higher yields. The yields are expected to increase under climate change scenarios but the yields would decline if only temperature rise is predominant (5-6%). If only CO2 rise continues without temperature rise the yields and WUE would continue to increase (6-7 %). It is proved that if CO2 increases even if temperature is bound to increase, in such situations the yields of all the cultivars increase (T2S3) it would be 1 – 4% and for treatment T3S4 it would be 2 – 4%. Similarly for WUE (yield) it would range between 1.0 – 5.5% for T2S3 and for T3S4 it would be 1.3 -5.4%. Varieties such as IR20, PR114 (high yielding) and NDR97 (temperature tolerant variety) that give more yields even under high temperature and water stress, responding to CO2 fertilization effect can be recommended for farming in SW plains of Uttarakhand state.

Keywords: Climate Change, CO2 fertilization effect, Rice, CERES-Rice, WUE