Setting the System Boundaries of “Energy for Water” for Integrated Modeling

Abstract

M any studies over the last two decades have addressed the "water-energy nexus," generally defined as the interdependency between water and energy in their supply, processing, distribution, and use. The research community currently disaggregates the water-energy nexus into two components: "water for energy" and "energy for water." While there seems to be clear consensus on the definition of "water for energy"that is, water required for the extraction, processing, and transformation of energy as well as the irrigation of bioenergythere has been less agreement on the definition and system boundaries of "energy for water." We represent six integrated assessment modeling teams presently incorporating the hydrologic system and water demands into existing global models of energy, agriculture, land use, and climate. In this article, we propose system boundaries of "energy for water" that are appropriate for integrated energy and water modeling, and introduce a third category of processes that are relevant for the water-energy nexus, but that are not logically classified as either "water for energy" or "energy for water."

Global and Regional Evaluation of Energy for Water

“…Considering several prominent sources of uncertainty, this corresponds to between 1.7% and 2.7% of total global primary energy consumption (Figure 6), comparable with the estimate of less than or equal to 3% by Williams and Simmons. 24 As our system boundaries for E4W include only processes where water is the output (Section 1) and exclude processes where energy is applied to water for other purposes, 25 our estimate of 1.0%− 1.9% for the United States is much lower than the 47% estimated by Sanders and Webber. 20 While 1.7%−2.7% may not appear significant, it nevertheless represents a large quantity of energy and therefore also a significant source of greenhouse gas emissions.…”

“…When included, these processes tend to account for the vast majority of estimated E4W. However, as explained in Kyle et al, 25 we exclude processes whose primary output is not water from the system boundaries of "energy for water." Instead, these activities are classified as "water and energy for other purposes" and will be addressed in subsequent research.…”

City-level water-energy nexus in Beijing-Tianjin-Hebei region

“…Gleick (1994) [1] brought up with the 'water-energy nexus' concept and elaborated water-related energy processes and energy-related water processes. Kyle et al (2016) [38] also proposed that 'water for energy' or 'energy for water' should only refer to water or energy used for processes whose main output is energy or water, and therefore end-use demands and commodities are categorised as 'water and energy for other purposes'. Yet some broadened their research to end-use.…”

The Water–Energy Nexus of Megacities Extends Beyond Geographic Boundaries: A Case of Beijing

“…While there are other studies like Sanders and Webber (2012) that also claimed the energy applied to water end uses—including the residential, commercial, industrial, and even electric power sector—as the “energy for water,” therefore they estimated a much higher EFW as 12.6% of the United States's primary energy consumption. Kyle et al (2016) and Liu et al (2016) argued that the type of energy actually is the energy applied to “water for other purposes” and should not be included as the “energy for water.” The controversial about this indicates that different definition of the system boundaries of EFW will lead to different results of the EFW accounting.…”