基于水文过程的能源作物生命周期水足迹量化研究：以木薯燃料乙醇为例

It is widely known that energy, environment, and water are trinity but inter-conditioned. Fuel ethanol, as one of the representatives of biofuels, not only can reduce carbon emission, but also bring several potential issues such as water consumption and water pollution on the local water environment. To strengthen the management of water resources, the Chinese government emphasizes the double control on the total amount and quality of water consumption. Therefore, it is vital to improve the regional water resources management and water use efficiency for energy crops. The water footprint serves as a comprehensive indicator of water use efficiency and can be used to measure the combined potential impact of energy crops on water use. At present, the water footprint assessment of the energy crop planting stage cannot truly reflect the whole process of water use in the crop growth stage. Based on the limitations of existing evaluation methods for water footprints, this paper established a quantitative method for life cycle water footprint of energy crops based on hydrological processes to truly reflect the water balance of energy crops, by incorporating irrigation transport loss and other factors into the water footprint quantification system, and improving the grey water footprint algorithm based on nutrient emissions. The cassava ethanol was used as an example to analyze the spatial distribution characteristics of the whole life cycle water footprint of cassava ethanol. At the same time, it analyzes the potential impact of the future promotion of fuel ethanol on the local water environment. The results of the project not only provide a way of thinking for the improvement of the water footprint methodology, but also provide a decision-making reference for the optimization of local water resources management.

能源-环境-水三位一体却又互相制约。以燃料乙醇为代表的生物燃料在带来减排效益的同时，也给当地水环境带来水减少和水污染等问题。为加强水资源管理，中国政府提出对水资源消耗总量和强度进行双控。因此，科学合理地评价能源作物生命周期用水过程是提高区域水资源管理水平和用水效率的前提。水足迹作为评价用水效率的综合指标，可用来衡量能源作物对水资源利用造成的潜在影响。目前已有能源作物的水足迹评价无法真实反映作物生长阶段的用水全过程。基于此，本项目建立了基于水文过程的能源作物生命周期水足迹量化方法，将灌溉输送损失等要素纳入水足迹量化体系，同时基于营养物排放改进灰水足迹算法，力求真实反映能源作物的水足迹要素关联。项目以木薯乙醇为例，用该法分析其生命周期水足迹的空间分布，同时预测未来燃料乙醇全面推广对当地水环境的潜在影响。项目的研究结果不仅为水足迹方法论的完善提供一种思路，还能为当地水资源管理的优化提供决策参考。

以燃料乙醇为代表的生物燃料在带来减排效益的同时，也给当地水环境带来水减少和水污染等问题。科学合理地评价能源作物生命周期用水过程是提高区域水资源管理水平和用水效率的前提。本项目提出通过构建能源作物水足迹量化模型，以木薯燃料乙醇为研究案例，分析木薯生长过程的蓝水、绿水和灰水足迹的时空演化特征，并在此基础上与生命周期水足迹评价耦合，构建基于人工智能的能源作物水足迹评估模型，同时结合中国车用燃料乙醇发展规划与交通运输用能需求，考察燃料乙醇的全面推广对当地水环境带来的潜在影响。主要成果如下：（1）木薯乙醇的直接水足迹远大于间接水足迹，作物种植阶段是生命周期水足迹最集中的阶段。（2）2004-2020年间，两广地区木薯生产水足迹总体呈现下降趋势。水足迹表现出很高的空间相关性和强空间聚集性，水足迹高高聚集区(H-H)主要分布在广西北部和中部，低低聚集区(L-L)主要分布在广东经济发达地区。（3）采用ANN、SVM和RF方法对水足迹进行建模预测，不同人工智能方法对水足迹预测结果有不同的表现，总体上，组合模型7(Tmax, Tmin, P, Kc, H和SH)是综合表现性能最优水足迹评估模型。采用该组合模型对蓝水足迹进行预测时，预测偏差介于-5.98%和3.85%之间。（4）随着交通用能的低碳化，生物乙醇将在交通运输领域减碳上发挥重要作用。这意味着需要提供安全稳定的生物燃料原料来源。从两广地区的木薯乙醇发展来看，两广地区在两种不同用水情景下的水压力程度具有相似的空间分布特征，广西相对于广东普遍面临着更高的水压力。研究成果有利于加深对水足迹的认识，同时对于当地水资源管理者缓解农业水资源短缺、加强水资源管理具有一定参考价值。