SEBAL for detecting spatial variation of water productivity and scope for improvement in eight irrigated wheat systems

A methodology has been developed to quantify spatial variation of crop yield, evapotranspiration (ET) and water productivity (WPET) using the SEBAL algorithm and high and low resolution satellite images. SEBAL-based ET estimates were validated over an irrigated, wheat dominated area in the Yaqui Valley, Mexico and proved to be accurate (8.8% difference for 110 days). Estimated average wheat yields in Yaqui Valley of 5.5 t ha−1 were well within the range of measured yields reported in the literature. Measured wheat yields in 24 farmers’ fields in Sirsa district, India, were 0.4 t ha−1 higher than SEBAL estimated wheat yields. Area average WPET in the Yaqui Valley was 1.37 kg m−3 and could be considered to be high as compared to other irrigated systems around the world where the same methodology was applied. A higher average WPET was found in Egyptʹs Nile Delta (1.52 kg m−3), Kings County (CA), USA (1.44 kg m−3) and in Oldambt, The Netherlands (1.39 kg m−3). The spatial variability of WPET within low productivity systems (CV = 0.33) is higher than in high productivity systems (CV = 0.05) because water supply in the former case is uncertain and farming conditions are sub-optimal. The high CV found in areas with low WPET indicates that there is considerable scope for improvement. The average scope for improvement in eight systems was 14%, indicating that 14% ET reduction can be achieved while maintaining the same yield. It is concluded that the proposed methodology is accurate and that better knowledge of the spatial variation of WPET provides valuable information for achieving local water conservation practices in irrigated wheat.