Regional disparities in the beneficial effects of rising CO2 concentrations on crop water productivity

Rising atmospheric CO2 concentrations ([CO2]) are expected to enhance photosynthesis and reduce crop water use(1). However, there is high uncertainty about the global implications of these effects for future crop production and agricultural water requirements under climate change. Here we combine results from networks of field experiments(1,2) and global crop models(3) to present a spatially explicit global perspective on crop water productivity (CWP, the ratio of crop yield to evapotranspiration) for wheat, maize, rice and soybean under elevated [CO2] and associated climate change projected for a high-end greenhouse gas emissions scenario. We find CO2 effects increase global CWP by 10[0;47]%-27[7;37]% ( median[interquartile range] across the model ensemble) by the 2080s depending on crop types, with particularly large increases in arid regions (by up to 48[25; 56]% for rainfed wheat). If realized in the fields, the effects of elevated [CO2] could considerably mitigate global yield losses whilst reducing agricultural consumptive water use (4-17%). We identify regional disparities driven by differences in growing conditions across agro-ecosystems that could have implications for increasing food production without compromising water security. Finally, our results demonstrate the need to expand field experiments and encourage greater consistency in modelling the effects of rising [CO2] across crop and hydrological modelling communities.

大气中二氧化碳浓度（[CO₂]）的上升预计会促进光合作用并减少作物的水分利用（1）。然而，在气候变化的情况下，这些影响对未来作物生产和农业用水需求的全球意义存在很大的不确定性。在此，我们结合田间试验网络（1,2）和全球作物模型（3）的结果，针对高端温室气体排放情景下预计的二氧化碳浓度升高以及相关气候变化，对小麦、玉米、水稻和大豆的作物水分生产率（CWP，作物产量与蒸散量之比）提出一个空间上明确的全球视角。我们发现，到21世纪80年代，二氧化碳的影响使全球作物水分生产率提高了10[0;47]% - 27[7;37]%（模型集合的中位数[四分位距]），具体取决于作物类型，在干旱地区提高幅度尤其大（雨养小麦提高幅度可达48[25;56]%）。如果在田间得以实现，二氧化碳浓度升高的影响可能会大大减轻全球产量损失，同时减少农业耗水量（4 - 17%）。我们发现了由农业生态系统生长条件差异所导致的区域差异，这可能对在不损害水安全的情况下增加粮食生产产生影响。最后，我们的结果表明，有必要扩大田间试验，并鼓励在作物和水文建模领域更一致地对二氧化碳浓度上升的影响进行建模。