Encyclopedia
The relationship between water and energy is a strong one characterized as having integration and coupling as two important features. While energy is responsible for delivering water to the end-users, it needs energy in order to be generated, and water. In this paper, a thorough review is presented regarding the different relationships between water and energy in terms of (i) the significance of the close relationship between water and energy by means of water/energy generation and consumption. Water consumption, water cooling and heating must be taken into account in order to avoid the obstacles related to future use of water for energy generation; (ii) the measuring and monitoring technologies for the energy-water nexus, focusing attention on the variables that are interrelated in the water and energy sectors. In addition, the consequences of finding several parameters, unknown variables and unclear dependencies in measuring of energy usage in the applications of water usage should also be taken into account. Innovative developments including nanotechnology, biotechnology, and wireless networks, as sensor technologies, may resolve the challenges of sensing; (iii) the different key performance indication tools for assessing and quantifying this nexus by analyzing and categorizing recent case studies of the water energy nexus and applicable evaluation methods; and (iv) the different research dimensions conducted on this nexus.
- energy-water nexus,critical review,methods and tools
1. Introduction
Being essential for human life, energy and water are interrelated resources. Not only is water essential for drinking, crops cultivation, extracting fuels, generating power, and producing goods, but the life and health of ecosystems depend on water as well. At the same time, energy is found by humans by means of the conversion of (i) fossil fuel resources, (e.g., natural gas, coal, oil) and (ii) renewable resources such as water, wind, and the sun. Thanks to the energy generated, humans have created a vibrant civilization that reinforces food production, agriculture, industry, transportation, science, a comfortable life, and so on. Interrelated in various ways, energy and water are mutual in the sense that energy is necessary to secure water, to treat and desalinate water for the usage of humans, and to transfer water. Meanwhile, water is required to generate energy by extracting and operating fossil fuels, growing biofuels, and for cooling thermal power stations. Energy and water fulfill reciprocal functions in which working on one of them relies on the status of the other in terms of cost and availability [1][2].
Being essential for human life, energy and water are interrelated resources. Not only is water essential for drinking, crops cultivation, extracting fuels, generating power, and producing goods, but the life and health of ecosystems depend on water as well. At the same time, energy is found by humans by means of the conversion of (i) fossil fuel resources, (e.g., natural gas, coal, oil) and (ii) renewable resources such as water, wind, and the sun. Thanks to the energy generated, humans have created a vibrant civilization that reinforces food production, agriculture, industry, transportation, science, a comfortable life, and so on. Interrelated in various ways, energy and water are mutual in the sense that energy is necessary to secure water, to treat and desalinate water for the usage of humans, and to transfer water. Meanwhile, water is required to generate energy by extracting and operating fossil fuels, growing biofuels, and for cooling thermal power stations. Energy and water fulfill reciprocal functions in which working on one of them relies on the status of the other in terms of cost and availability [1,2].
A boom in studies on the topic has contributed to the interest that has been paid to the water-energy nexus (WEN). A very large spectrum of challenges, sizes, and the creation of several models and tools are addressed by the research undertaken. Themes range from conceptualization to case studies, but all are related to resource depletion and continuous condensation. The challenges include a very wide range of scales starting from micro-level to macro-level scales. Also, the studies’ scope includes city, regional, and international [3].
Different WEN studies use or expand a particular method and adopt this method to their characteristics. For example, many countries such as China and the United Kingdom use the developed models using the Foreseer online tool to meet their research demands with regard to the nexus. Other developed models are used to understand the nature of the WEN nexus in countries such as the United States and Australia [4].
Experiences and perceived benefits of replicating or changing these models and procedures in different situations can hardly be measured and compared. Until now, few studies have been conducted on WEN. Many of them concentrate on classifying types of approach such as physical model, saving analysis, interconnected indexes, and management model of optimization. A lot of these studies rely specifically on a specific sector or industry feature, and almost all the models have a water footprint [5].
2. The Energy-Water Nexus: Key Performance Indicator (KPI) Tools
This section provides a potential framework for investigating and ranking late contextual analyzes of the WEN nexus and the evaluation strategies applied. This aims to add to the advancement of WEN technologies that increase field value while reducing the duplication of endeavors. The key performance indicator (KPI) tools’ case studies are divided into four groups according to the scale and nature of their application: city level, regional level, national level and transboundary level.
2.1. Comprehensive Case Studies of Various Geographical Scales
2.1.1. City-Level Scale
Cities are the main hubs where water and energy flows mix. In cities, sources and sinks of water and energy are more complex and intensive than in rural regions. The city is considered as the core of WEN research. Globally, the selected studies include case cities around the world. For example, the study of the relationship between water, energy, food, and climate is conducted for an increasingly robust and maintainable urban framework in Africa [6]. On the island of Skiathos, Greece, water and energy are managed and the resources are sustained by comparing the various sectors that need energy—residential, industrial, commercial, agricultural, etc.—and by studying the correlation between them and the use of water [7]. In Beijing, China, this nexus is studied from both generation and usage perspectives, where input-output are used to analysis the consumption of water to generate energy [8].
2.1.2. Regional-Level Scale
Regularly covering a larger geographic area, large-scale inspections at the regional level generally rely on river basins, including urban areas as well as more extensive drainage areas. The water–energy relationship has developed over the past decade. The systematic structures of principles applied and established between those checks include, for example, water assessment and planning (WEAP), long-term energy alternatives planning (LEAP), and coordinated WEAP and LEAP for a better understanding of the global energy grid on a regional scale [9], and the integrated model system for New South Wales [10]. All works applied the systematic structures and their objectives are for policy requirements and helping the decision maker by focusing on articulating the synergies of integrated resource planning and the trade-offs between them.
2.1.3. National-Level Scale
Policy-making and management analysis in arranging resources are the main concerns of tests at the national level. In terms of policy needs and major difficulties, water need, and water system pressure appear in the bulk of the national audited levels considered by the WEN [11][12][13][14][15]. For example, the heavily petroleum-dominated WEN in three countries (Kuwait, Qatar and Saudi Arabia) of the Gulf Cooperation Council (GCC) uses the information obtained across local scales and along the time to assess the nexus and detect the stresses on the nexus [16]. The oil exports income in the GCC makes it possible for the country to compensate for the shortage in the supply of water.
2.1.4. Transboundary-Level Scale
Cross-border assets and arrangements in some major regions over a few states are more intertwined than those in a single city or state. Management authorities at the transboundary level need to adjust the needs of the proximal network with the needs of society and the more inclusive situation [17]. The incomparable Mekong River Basin is a model for delegates [17][18][19]. Part of the current investigations recommended that the nexus approach would likely be beneficial to partners to understand the links between resources and policies [17][18][19], and they proposed an interconnected system that joined some specific models to investigate water, energy and food security in the Mekong River Basin. Similar examinations, for example, in the Euphrates–Tigris waterway basin [20] and the Amu Darya Basin in Central Asia [21] have suggested their own interconnected model structures to investigate how benefits are shared between those states.
Figure 4.
2.2. Water–Energy Nexus (WEN) KPI Tools
There are different KPI tools for assessing the water–energy relationship [22]. Until recently, the most important of these tools and techniques were used for sectoral assessment, whether in water or energy. For example, the MODISM model for simulating and evaluating water quality and quantity [23], and the LEAP software tool designed by the Stockholm Environment Institute for Energy Planning and Energy Policy Analysis [24]. There are six KPI tools used to assess the relationship between water and energy.
There are different KPI tools for assessing the water–energy relationship [115]. Until recently, the most important of these tools and techniques were used for sectoral assessment, whether in water or energy. For example, the MODISM model for simulating and evaluating water quality and quantity [116], and the LEAP software tool designed by the Stockholm Environment Institute for Energy Planning and Energy Policy Analysis [117]. There are six KPI tools used to assess the relationship between water and energy.
2.2.1. Energy Density (EI)
EI (energy density) is a top-down and bottom-up hybrid model used to quantify energy flows in a civilian water frame. The top-down model is planned to generate high-level calculations of energy intensity per month for the civil water framework. The bottom-up model is designed to estimate energy calculations in detail for a subset of the civil water framework. It is an estimation tool used in the case study of the Municipal Utilities District in East Bay in Northern California [25], but this tool has neither a strategic role nor a viable program.
2.2.2. Jordan Framework
This frame consists of three connected parts. The first is a quantitative test portion that designs the water and energy physical joints to assess the major subsections within the water and energy fields. The second part is the stakeholder testing of energy and water policy authorities and is used to uncover key actors and agencies. Part three used the findings from the previous section to uncover the controlled stakeholders who could be intermediaries for the transit of the primary water and energy leadership. This structure was effectively used for the case study of Jordan [26].
2.2.3. Correlation Analysis
Correlation analysis, drawn from the testing of inputs and outputs, is used to determine direct and indirect resource uses as well as the function of each financial branch (such as resource generation or resource uses) [27]. In the case of Beijing, correlation analysis was used to examine summarized water and energy capacity between urban finance departments [28]. For this case study, the correlation analysis has been modified to a hypothetical extraction method (HEM), which isolates the impacts of financial activities on resources into four divisions: internal impact (IE), mixed effect (ME), and net or external backlink. (NBL), and net or external front link (NFL).
2.2.4. Multi-Territory Nexus Network (MRNN)
MRNN (multi-territory nexus network), joined with the multi-regional input-output model (MRIO) and environmental network analysis model (ENA), is an integrated model created to fundamentally evaluate water and water energy for city energy and regional scales [29]. The MRIO model can assess water currents or indirect energy, to calculate the amount required to create products and projects based on sectoral cooperation and trade in a complex framework [30]. Instead of the MRIO model, the ENA model can use dynamic flows to evaluate not only direct and indirect resource flows in making change, but also the links between financial departments [31][32]. ENA can also track patterns of energy use or inversely use water to represent the overall use or use involved, and reveal features of frame structure and capacity [33]
2.2.5. A Dynamic Approach to the System
To understand the provincial water and energy resource arrangement in the long run, Zhuang [34] built a dynamic model of an integrated framework which was a four-step procedure model including the steps of the structure test, the structured behavior test of the structure, the implementation test and the attitude plan estimation.
2.2.6. Optional Urban Water Driving Tool (UWOT)
The UWOT (optional urban water driving tool) is also a tool that focuses on urban water frameworks [35][36][37]. It has four advantages: (1) evaluation of optional media to reduce consumer water demand; (2) energy assessments required by water devices; (3) assessment of beneficial uses of volumes of runoff and waste; and (4) evaluating the advantages of green areas on the urban heat island effect. This tool was used to create and quantify much of the “evidence” towards wastewater reuse for urban water arrangement in Athens [38]. Baki and Makropoulos [39] broaden UWOT to display the energy impression within urban water supply frameworks and discuss the use of this tool in the dynamic economic arrangement and effective management of water and energy resources in urban communities.
The UWOT (optional urban water driving tool) is also a tool that focuses on urban water frameworks [128,129,130]. It has four advantages: (1) evaluation of optional media to reduce consumer water demand; (2) energy assessments required by water devices; (3) assessment of beneficial uses of volumes of runoff and waste; and (4) evaluating the advantages of green areas on the urban heat island effect. This tool was used to create and quantify much of the “evidence” towards wastewater reuse for urban water arrangement in Athens [131]. Baki and Makropoulos [132] broaden UWOT to display the energy impression within urban water supply frameworks and discuss the use of this tool in the dynamic economic arrangement and effective management of water and energy resources in urban communities.
