Abstract
Accurate information about the spatiotemporal variability of actual crop evapotranspiration (ETa), crop coefficient (Kc) and water productivity (WP) is crucial for water efficient management in the agriculture. The Earth Engine Evapotranspiration Flux (EEFlux) application has become a popular approach for providing spatiotemporal information on ETa and Kc worldwide. The aim of this study was to quantify the variability of water consumption (ETa) and the Kc for an irrigated commercial planting of soybeans based on the EEFlux application in the western region of the state of Bahia, Brazil. The water productivity (WP) for the fields was also obtained. Six cloud-free images from Landsat 7 and 8 satellites, acquired during the 2016/17 soybean growing season were used and processed on the EEFlux platform. The ETa from EEFlux was compared to that of the modified FAO (MFAO) approach using the following statistical metrics: Willmot’s index of agreement (d-index), root mean square error (RMSE), mean absolute error (MAE) and mean bias error (MBE). The Kc from EEFlux was compared to the Kc used in the soybean field (Kc FAO-based) and to the Kc values obtained in different scientific studies using the d-index. A similar procedure was performed for WP. Our results reveal that EEFlux is able to provide accurate information about the variability of ETa and the Kc of soybean fields. The comparison between ETa EEFlux and ETa MFAO showed good agreement based on the d-index, with values of 0.85, 0.83 and 0.89 for central pivots 1, 2 and 3, respectively. However, EEFlux tends to slightly underestimate ETa. The Kc EEFlux showed good accordance with the Kc values considered in this study, except in phase II, where a larger difference was observed; the average WP of the three fields (1.14 kg m-3) was higher than that in the majority of the previous studies, which is a strong indicator of the efficient use of water in the studied soybean fields. The study showed that EEFlux, an innovative and free tool for access spatiotemporal variability of ETa and Kc at global scale is very efficient to estimate the ETa and Kc on different growth stages of soybean crop.
Highlights
One of the great current and future challenges worldwide is the production of more food to serve a growing population, which in 2050 can reach 9.73 billion people [1], in a scenario with less water available for agriculture
The Earth Engine Evapotranspiration Flux (EEFlux) platform has recently developed a METRIC version that operates on the Google Earth Engine (GEE) system [16,18]
Precise information about the spatiotemporal variability of actual crop evapotranspiration (ETa) and crop coefficient (Kc) is crucial for water efficient management in the agriculture, which is the largest user of freshwater in the world
Summary
One of the great current and future challenges worldwide is the production of more food to serve a growing population, which in 2050 can reach 9.73 billion people [1], in a scenario with less water available for agriculture. In the specific case of irrigated agriculture, management is even more important because it represents the largest user of freshwater in the world, being responsible for approximately 70% of freshwater consumption, which is withdrawn from surface water and groundwater resources [1]. Zhang et al [4] mentioned that, currently, irrigation depth is still often applied based on experience instead of science. To overcome this issue and improve water use in agriculture, Kamali & Nazari [5] reported that two main strategies can be used: (i) upgrading operationally inefficient irrigation systems and (ii) improving irrigation planning and management
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