Abstract 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.

中文翻译：

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全球农田初级生产总值、蒸散量和用水效率的变化

摘要 更好地了解全球农田的生产力和用水效率 (WUE) 对于应对不断增长的粮食和水需求至关重要。目前，WUE 的时空分布和趋势以及相关的农田初级生产总值 (GPP) 和蒸散量 (ET) 在全球范围内仍然很难量化，特别是考虑到雨养和灌溉条件之间的差异。在本研究中，中分辨率成像光谱仪 (MODIS) 产品和新开发的全球粮食安全支持作物优势分析数据产品 (GFSAD1KCD) 被用于量化和分析全球 GPP、ET 和 WUE 的时空变化和年度趋势。 2000 年至 2014 年的耕地。该分析补充了来自重力恢复和气候实验的总蓄水量数据。结果表明，GPP 最高的农田具有最高的 ET。全球农田的平均 WUE 为 1.73 g C kg−1 H2O，从灌溉农田的较低平均值 1.62 g C kg−1 H2O 到雨育农田的较高平均值 1.83 g C kg−1 H2O。灌溉农田的 WUE 通常低于雨育农田；由于灌溉农田 WUE 的显着增加趋势和雨育农田 WUE 的显着下降趋势，这种差异在 2000-2014 年期间有所下降。然而，观察到的灌溉农田 WUE 的增加并不一定与地下水枯竭的减少重叠，如总蓄水量相应的显着下降趋势所示。事实证明，GFSAD1KCD 数据可用于调查全球农田的初级生产和 WUE，特别是在灌溉和雨育条件之间的比较中。未来的研究应侧重于减少与灌溉农田分布相关的不确定性，以便在全球范围内更好地量化和了解 WUE。