Water and Carbon Footprints of Electricity Are Sensitive to Geographical Attribution Methods

Abstract

Environmental footprinting methods provide a means to relate the environmental externalities of electricity production to electricity consumers. Although several methods have been developed to connect the environmental footprint of electricity generation to end users, estimates produced by these methods are inherently uncertain due to the impossibility of actually tracing electricity from the point of generation to utilization. Previous studies rarely quantify this uncertainty, even though it may fundamentally alter their findings and recommendations. Here, we evaluate the sensitivity of water and carbon footprints estimates among seven commonly used methods to attribute electricity production to end users. We assess how sensitive water and carbon electricity footprint estimates are to attribution methods, how these estimates change over time, and the main factors contributing to the variability between methods. We evaluate and make available the water and carbon footprints of electricity consumption for every city across the contiguous United States for all assessed methods. We find significant but spatially heterogeneous variability in water and carbon footprint estimates across attribution methods. No method consistently overestimated or underestimated water and carbon footprints for every city. The variation between attribution methods suggests that future studies need to consider how the method selected to attribute environmental impacts through the electrical grid may affect their findings.

Water for energy: Characterizing co‐evolving energy and water systems under twin climate and energy system nonstationarities

“…Similarly, choices to include rain water (in water footprinting parlance, green water [Hoekstra et al, 2011]) or polluted water volumes (gray water [Hoekstra et al, 2011]) vary by study (Chini et al, 2020; Marston et al, 2018), though green water is mainly relevant for systems including agriculture and/or silviculture (Grubert et al, 2020). When the water use of electricity in a specific area is the quantity of interest, challenges also arise in determining the relevant geographic attribution of water used for electricity (Siddik et al, 2020).…”

“…Similarly, choices to include rain water (in water footprinting parlance, green water [Hoekstra et al, 2011]) or polluted water volumes (gray water [Hoekstra et al, 2011]) vary by study (Chini et al, 2020;Marston et al, 2018), though green water is mainly relevant for systems including agriculture and/or silviculture (Grubert et al, 2020). When the water use of electricity in a specific area is the quantity of interest, challenges also arise in determining the relevant geographic attribution of water used for electricity (Siddik et al, 2020). One major conflict in volumetric water use assessment (Gerbens-Leenes et al, 2021) regards the water footprinting method's preference for volumetric inventory measures alone, treating water use as resource depletion (Hoekstra, 2016) due to the potential for virtual water trade to allocate such use based on availability (Chapagain & Hoekstra, 2008;Chini et al, 2018;He et al, 2019).…”

The Water Footprint of the United States

“…Fuel and electricity constitute much of the remainder of a city's indirect water footprint of consumption. The contribution of energy in a city's water footprint of consumption varies significantly between cities depending on their energy portfolio and its water intensity [48,52]. Due to the unique properties of the electricity grid, the water footprint of electricity consumption varies widely depending on the methodology employed to attribute water consumed in electricity production to the final consumer [48].…”

“…Grubert [47] built on the global study by AYH, using detailed, facility-specific data within the US to estimate the blue water footprint for nearly 2200 hydropower facilities. Water footprint assessments are highly sensitive to the methodology used to calculate the water footprint of hydropower and the inclusion of hydropower in the water footprint of energy production studies can skew results due to relatively large volumes of water consumption attributed to this form of energy generation [47,48].…”

Past, Present, and Future of Virtual Water and Water Footprint

“…In the past two decades, the introduction of the concept of the ecological footprint has driven the development of other footprint indicators in the field of resource utilization and environmental impact assessment [33]. A series of footprint indicators such as water footprint, carbon footprint, nitrogen footprint, energy footprint, land footprint, and biodiversity footprint came into being [55][56][57], which have substantially enriched the quantitative assessment indicators of the influence of human activities on the ecosystem [58].…”