European Commission, Joint Research Centre (JRC), Ispra, Italy.
Department of Civil, Construction and Environmental Engineering, University of Alabama, Tuscaloosa, AL, United States.
Sci Total Environ. 2021 Feb 20;756:143992. doi: 10.1016/j.scitotenv.2020.143992. Epub 2020 Nov 28.
To evaluate the environmental sustainability of blue water use or the blue water footprint (WF) of a product, organisation, geographical entity or a diet, two well-established indicators are generally applied: water efficiency and blue water stress. In recent years, the Life Cycle Assessment (LCA) community has developed, used and promoted the indicator scarcity-weighted WF, which aims to grasp both blue water use and blue water stress in one indicator. This indicator is now recommended in an ISO document on water footprinting and many scholars have used associated scarcity-weighted water use indicators. However, questions on its physical meaning and its ability to correctly evaluate water sustainability have emerged. Here, we analyse for global irrigated wheat production to what extend the scarcity-weighted WF addresses blue water stress and water efficiency. We observe inconsistent results, as a significant proportion of unsustainably produced irrigated wheat has better scarcity-weighted WF scores as compared to sustainably produced irrigated wheat. Using the scarcity-weighted WF or scarcity-weighted water use for policy-making including product labelling, punishes some farmers producing their wheat in a water-sustainable way and promotes some farmers producing wheat unsustainably. Applying the scarcity-weighted WF indicator thereby is contraproductive in reaching the Sustainable Development Goal (SDG) target 6.4 on reducing water stress. In line with the specifications of this SDG target, to evaluate the sustainability of blue water use or the blue WF, the two indicators water stress and water efficiency should be used separately, in a complementary way.
为了评估蓝水利用的环境可持续性或产品、组织、地理实体或饮食的蓝水足迹（WF），通常应用两个成熟的指标：水效率和蓝水压力。近年来，生命周期评估（LCA）界开发、使用和推广了稀缺性加权 WF 指标，旨在用一个指标来同时把握蓝水利用和蓝水压力。该指标现被一份关于水足迹的 ISO 文档推荐，许多学者也使用了相关的稀缺性加权用水指标。然而，关于其物理意义及其正确评估水可持续性的能力的问题已经出现。在这里，我们分析了全球灌溉小麦生产，以了解稀缺性加权 WF 在多大程度上解决了蓝水压力和水效率问题。我们观察到不一致的结果，因为相当一部分不可持续生产的灌溉小麦的稀缺性加权 WF 得分优于可持续生产的灌溉小麦。在包括产品标签在内的政策制定中使用稀缺性加权 WF 或稀缺性加权用水量会惩罚一些以可持续方式生产小麦的农民，并促进一些农民不可持续地生产小麦。因此，应用稀缺性加权 WF 指标在实现可持续发展目标 6.4 减少水压力方面是适得其反的。根据这一 SDG 目标的规范，为了评估蓝水利用的可持续性或蓝 WF，应分别使用水压力和水效率这两个指标，以互补的方式使用。
