Variability mapping of crop evapotranspiration for water footprint assessment at basin level

Knowledge about variability in crop evapotranspiration (ETc) is essential for realistic assessment of crop water footprint. In this study, administrative districts falling under the Gomati basin were divided into 21 Agricultural Production Units (APUs) on the basis of homogeneity of soil and agro-ecology. Blue and green components of ETc of 15 major crops grown in each APU were assessed using CROPWAT model. Ordinary kriging and ordinary co-kriging were evaluated for mapping spatial variability of ETc. Prediction error was lowest for ordinary cokriging. Etc variability maps for kharif and rabi crops were developed using ordinary co-kriging. In case of kharif crops, the maximum Etc was observed in the central region while that for rabi crops it was in the lower region of the Gomati basin. Variability in green crop water use was high. Green water use by paddy was 425.0 mm, 420.4 mm and 410.4 mm in the lower, upper and middle regions, respectively. The green water use of winter crops varied from 0.2 mm for mustard to 25.8 mm for wheat crop. In general, the blue water use by rabi crops was considerably higher than that of kharif crops and it varied from 5.3 to 942.5 mm for maize and sugarcane, respectively. Sugarcane had maximum blue and green water use. In view of large variations, estimation of crop water footprint considering average value of ETc for entire basin will not be appropriate.