Ai, ZP; Wang, QX; Yang, YH; Manevski, K; Yi, S; Zhao, X (2020). Variation of gross primary production, evapotranspiration and water use efficiency for global croplands. AGRICULTURAL AND FOREST METEOROLOGY, 287, 107935.

An improved understanding of the productivity and water use efficiency (WUE) of global croplands is essential for coping with the growing demand for food and water. At present, the spatiotemporal distribution and trends of WUE and the associated gross primary production (GPP) and evapotranspiration (ET) for croplands remain poorly quantified at the global scale, especially considering the differences between rainfed and irrigated conditions. In this study, the Moderate Resolution Imaging Spectroradiometer (MODIS) products and the newly developed Global Food Security-support Analysis Data product of Crop Dominance (GFSAD1KCD) were utilized to quantify and analyze spatiotemporal variation and annual trends in GPP, ET and WUE for global croplands from 2000 to 2014. The analysis was complemented with total water storage data from the Gravity Recovery and Climate Experiment. The results showed that the croplands with the highest GPP had the highest ET. The mean WUE of global croplands was 1.73 g C kg(-1) H2O, ranging from a lower mean value of 1.62 g C kg(-1) H2O for irrigated croplands to a higher mean value of 1.83 g C kg(-1) H2O for rainfed croplands. Irrigated croplands generally had lower WUE than rainfed croplands; this difference decreased during 2000-2014 owing to a significantly increasing trend in WUE for irrigated cropland and a significantly deceasing trend in WUE for rainfed croplands. However, the increase in WUE observed for irrigated croplands did not necessarily overlap with the decrease in groundwater depletion, as indicated by the corresponding and significantly decreasing trend of total water storage. The GFSAD1KCD data proved useful for investigating primary production and WUE for global croplands, especially in comparisons between irrigated and rainfed conditions. Future studies should focus on reducing the uncertainty associated with the distribution of irrigated croplands in order to better quantify and understand WUE on a global scale.