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The objective of this study was to determine the water requirement and crop coefficient of the irrigated sugarcane, variety RB 92-579, in the semi-arid region of the lower middle of Sao Francisco Valley. The experiment was carried out in a commercial area of sugarcane located in the municipality of Juazeiro in the State of Bahia. The crop water requirement was estimated with the Bowen Ratio Energy Balance method. The accumulated biomass and the photosynthetic active radiation intercepted (f(PAR)) by the crop were monitored. The sugarcane evapotranspiration reached a mean value of 4.7 mm d(-1) in response to f(PAR) and accumulated biomass; however presented influence of the crop lodging during the maximum growth phase. The total water requirement of the sugarcane ratoon was 1710 mm. Crop coefficient reached a mean value of 1.10 in the phase of maximum growth. The equations adjusted for monthly crop coefficient, using the growing degree days and days after the harvest as independent variables presented good performance (R-2 similar to 0.95 and 0.98) and, consider the reduction in the Kc values because of crop lodging.