Maize (Zea mays L.) is predominantly grown as a commercial crop in river basins of lower Krishna, Telangana, South India. A long-term crop water balance analysis for maize in two sowing windows (normal sowing: 20 June; late sowing: 25 July) was done for A1b climate change scenario using the down-scaled climate data from the GCM model ECHAM5. The crop water balance parameters such as rainfall, effective rainfall, crop evapotranspiration (ET) and irrigation requirements of maize during the two sowing windows were estimated using the CROPWAT model for the base period (1961-90) and long-term period (2011-50; mid-century). In the normal sowing window of maize, there was significant variation in the decadal crop ET (24% to 28%) and irrigation requirements (-7% to 26%) having increasing trend during 2011-2050 over base period. The amount of average decadal rainfall and effective rainfall decreased during 2011-2050 in the range 6% to -23% and 10% to -7% respectively, over the base period. The decadal average rainfall and effective rainfall showed increasing trends of 147-151% and 96-110% respectively, over base period in late sowing window. Also, the crop ET and irrigation requirements exhibited a decreasing trend. The study indicates a shift in the seasonal rainfall in normal sowing window during June to July and it extends up to October and November after the season, indicating more rainfall in late sowing window of maize and scope for rainwater harvesting in the lower Krishna river basin for sustaining maize production.