Water-energy nexus: The origin, development and prospect

Water footprint and virtual water trade analysis in water-rich basins: Case of the Chaohu Lake Basin in China

Water footprints and virtual water are widely used as essential tools for water use and conservation analysis of basins worldwide. Despite the importance of water-rich basins as the main force for water-saving, water use analysis has been mainly for water-scarce basins rather than water-rich basins in the existing literature. To fill the gap, in this paper, we investigate the water footprint and virtual water trade in a water-rich basin, namely the Chaohu Lake Basin in China, from 2007 to 2017 using input-output analysis. The results show that: (1) Water use efficiency in the Chaohu Lake Basin was significantly improved. The overall trend of the water intensity was declining, decreasing by 10.21 % in 2017 versus 2012; (2) The internal and external water footprints showed an upward trend, and the growth rate of total water footprint was 36.66 %; (3) The basin was a net virtual water exporter, but the net export flows of virtual water has decreased significantly. The virtual water net export flow decreased by 0.12 billion m³ in 2017 versus 2012; (4) Water resources in the basin were mainly used locally, and its supply to other provinces was minimal. Compared with some water-scarce basins such as the Heihe River Basin and Haihe River Basin, the Chaohu Lake Basin shows significant gaps in the virtual water export flow per capita and behaves differently in the proportion of virtual water transfer. Based on the above findings, we conclude with some guidance and implications for local governments and policymakers.

Spatially Explicit River Basin Models for Cost-Benefit Analyses to Optimize Land Use

Recently, a wide range of models have been used in analyzing the costs and benefits of land utilization in river basins. Despite these advances, there is not enough information on how to select appropriate models to perform cost-benefit analyses. A literature search in the Web of Science (WOS) online database was implemented and resulted in the selection of 27 articles that utilized models to perform cost-benefit analyses of river basins. The models reviewed in these papers were categorized into five types: process-based, statistical, probabilistic, data-driven, and modeling frameworks or integrated models. Twenty-six models were reviewed based on their data and input variable needs and user convenience. A SWOT analysis was also performed to highlight the strengths, weaknesses, opportunities, and threats of these models. One of the main strengths is their ability to perform scenario-based analyses while the main drawback is the limited availability of data impeding the use of the models. We found that, to some extent, there is an increase in model applicability as the number of input variables increases but there are exceptions to this observation. Future studies should explicitly report on the necessary time needed for data collection, model development and/or training, and model application. This information is highly valuable to users and modelers when choosing which model to use in performing a particular cost-benefit analysis. These models can be developed and applied to assist sustainable development as well as the sustainable utilization of agricultural parcels within a river basin, which can eventually reduce the negative impacts of intensive agriculture and minimize habitat degradation on water resources.

Analysis of the Water-Energy Nexus Applied to an Insular System: Case Study of Tenerife

Insular territories face important challenges in achieving effective sustainable development, mainly due to low internal availability of basic resources, which results in a high external dependency. The analysis of the energy–water nexus of islands is a powerful instrument to evaluate the sustainable goals of the region and to identify the key actions to take to fulfill these objectives in future scenarios. The aim of this study is to review the energy–water nexus applied to Tenerife (Canary Islands), considering three scenarios: the base case scenario, corresponding to the current situation, where 1.1% of consumed water is dedicated to energy production and 10.2% of the energy is supplied for water abstraction, depuration, and ocean discharge; and two projections for the year 2050: a maintained trend scenario, and an ecology-aware scenario, where the population growth and the deployment of electrical vehicles are considered. In 2018, the total energy consumed was 1954 ktoe, of which renewable energy made up 2%. In the maintained trend scenario, this amount rises to 2003 ktoe, of which renewable energies represent 29%. However, in the ecology-aware scenario, this amount could be reduced to 1710 ktoe of which 51% of energy is obtained from renewable sources.

Exploring the driving forces on sustainable energy and water use in China

With the rapid growth of global demand for water and energy, the two increasingly restrict economic and social development. The total energy consumption and water use are positively correlated. Identifying the key drivers influencing the energy-water development can realize national resource management and sustainable supplement. In this context, this study aims to capture the key driving forces that affect the sustainable energy-water development characteristics in Chinese change processes throughout 2000-2017. Five driving forces, the EW intensity effect, industrial structure effect, GDP value-added effect, income improvement effect, and population-scale effect, were further decomposed by the logarithmic mean Divisia index (LMDI) model to explore the energy consumption and water use. Our findings indicated that the largest and lowest energy consumers were the manufacturing and construction sectors, while agriculture accounted for the largest share in water use. During the three time intervals, the cumulative effects increased the EW use, but the contributions were declining. Further, these effects had a more prominent influence on water use than energy consumption; GDP value-added effect, income improvement effect, and population-scale effect increased the EW use, while intensity effect played a vital role in decreasing EW use during the study period. Notably, the industrial structure effect had a seesaw role during 2000-2006, which led to a tradeoff between various driving factors. In future sustainable issues, policymakers should pay more attention to energy-saving than water-saving to achieve the national energy and water conservation targets.

Advancing the representation of reservoir hydropower in energy systems modelling: The case of Zambesi River Basin

In state-of-the-art energy systems modelling, reservoir hydropower is represented as any other thermal power plant: energy production is constrained by the plant’s installed capacity and a capacity factor calibrated on the energy produced in previous years. Natural water resource variability across different temporal scales and the subsequent filtering effect of water storage mass balances are not accounted for, leading to biased optimal power dispatch strategies. In this work, we aim at introducing a novelty in the field by advancing the representation of reservoir hydropower generation in energy systems modelling by explicitly including the most relevant hydrological constraints, such as time-dependent water availability, hydraulic head, evaporation losses, and cascade releases. This advanced characterization is implemented in an open-source energy modelling framework. The improved model is then demonstrated on the Zambezi River Basin in the South Africa Power Pool. The basin has an estimated hydropower potential of 20,000 megawatts (MW) of which about 5,000 MW has been already developed. Results show a better alignment of electricity production with observed data, with a reduction of estimated hydropower production up to 35% with respect to the baseline Calliope implementation. These improvements are useful to support hydropower management and planning capacity expansion in countries richly endowed with water resource or that are already strongly relying on hydropower for electricity production.

Indicators of Land, Water, Energy and Food (LWEF) Nexus Resource Drivers: A Perspective on Environmental Degradation in the Gidabo Watershed, Southern Ethiopia

In Ethiopia, land, water, energy and food (LWEF) nexus resources are under pressure due to population growth, urbanization and unplanned consumption. The effect of this pressure has been a widely discussed topic in nexus resource literature. The evidence shows the predominantly negative impact of this; however, the impact of these factors is less explored from a local scale. As a result, securing nexus resources is becoming a serious challenge for the country. This necessitates the identification of the driving factors for the sustainable utilization of scarce LWEF nexus resources. Our study provides a systemic look at the driving factor indicators that induce nexus resource degradation. We use the Analytical Hierarchical Process (AHP) to develop the indicators’ weights, and use a Path Analysis Model (PAM) to quantitatively estimate the effect of the driving factor indicators on the LWEF nexus resources. The results indicate that social (48%), economic (19%), and policy and institutional changes (14%) are the major nexus resource driving factor indicators. The path analysis results indicate that among the social driving factor indicators, population growth and consumption patterns have a significant direct effect on the LWEF nexus, with path coefficients of 0.15 and 0.089, respectively. Similarly, the potential of LWEF nexus resources is also influenced by the institutional and policy change drivers, such as outdated legislation and poor institutional structure, with path coefficients of 0.46 and 0.39, respectively. This implies that population growth and consumption patterns are the leading social drivers, while outdated legislation and poor institutional structures are the institutional and policies change drivers which have a potential impact on LWEF nexus resource degradation. Similarly, other driving factors such as environmental, economic and technological factors also affect nexus resources to varying degrees. The findings of our study show the benefits of managing the identified driving factors for the protection of LWEF nexus resources, which have close links with human health and the environment. In order to alleviate the adverse effects of driving factors, all stakeholders need to show permanent individual and collective commitment. Furthermore, we underline the necessity of applying LWEF nexus approaches to the management of these drivers, and to optimize the environmental and social outcomes.

Governing the energy-water nexus in China: An analysis from the perspective of the science-policy interface

China is facing great water and energy pressure due to industrialization, urbanization, population growth and environmental change. China's explosive economic development has come at a steep cost in terms of natural resource exploitation and environmental problems. These unintended negative consequences are partly the result of a narrow single-sector management approach to natural resources, which often caused conflicts and low efficiency of related policies. Although the nexus approach is beneficial for optimization of natural resource utilization and development, the question of whether it can be applied in policy and practice is determined by various factors. The science-policy interface that stresses the political and social contexts provides a useful perspective for understanding the process of the nexus approach, from the scientific domain to policy. Combining criteria of good governance and an effective science-policy interface, suggestions for promoting good energy-water nexus governance are put forward, including popularization of scientific knowledge about the nexus in the political and social fields, collaborative governance of the nexus, and accelerating good governance of the whole of society.