Urban water and energy systems are crucial for sustainably meeting basic service demands in cities. This paper proposes and applies a technology-independent “reference resource-to-service system” framework for concurrent evaluation of urban water and energy system interventions and their ‘nexus’ or ‘interlinkages’. In a concrete application, data that approximate New York City conditions are used to evaluate a limited set of interventions in the residential sector, spanning from low-flow toilet shifts to extensive green roof installations. Results indicate that interventions motivated primarily by water management goals can considerably reduce energy use and contribute to mitigation of greenhouse gas emissions. Similarly, energy efficiency interventions can considerably reduce water use in addition to lowering emissions. However, interventions yielding the greatest reductions in energy use and emissions are not necessarily the most water conserving ones, and vice versa. Useful further research, expanding the present analysis should consider a broader set of resource interactions, towards a full climate, land, energy and water (CLEW) nexus approach. Overall, assessing the impacts, trade-offs and co-benefits from interventions in one urban resource system on others also holds promise as support for increased resource efficiency through integrated decision making.

In an increasingly urban world, developing sustainable cities is crucial for global sustainability. Urban nature-based solutions (NBS), such as green infrastructure, are often promoted for their potential to provide several urban services. These include storm-water mitigation, improving energy efficiency of buildings and carbon emissions mitigation, but few studies have compared the multi-functionality of NBS to conventional urban solutions providing similar services. Fewer yet have acknowledged the indirect resource (specifically Climate, Land, Energy, Water (CLEW) nexus) impacts that these solutions may have. This paper analyses these aspects, employing a simple CLEW nexus accounting framework, and attempts a consistent comparison across different resource systems. The comparison includes direct and indirect impacts of a set of stylized – and diverse – solutions, each with different primary objectives: green roofs, representing a multi-functional urban NBS; permeable pavements targeting mitigation of storm-water flows; window retrofits targeting energy efficiency; and roof-top PV installations targeting CO₂ emissions mitigation. The results highlight both the direct and total (CLEW nexus) impacts of green roofs on storm-water retention, energy use, and CO₂ emissions. However, also for the studied conventional solutions with primarily a single direct function, CLEW nexus impacts spread across all measured dimensions (energy, water, CO₂) to varying degrees. Although the numerical results are indicative and uncertainty needs to be further assessed, we suggest that the development of this type of multi-functional, multi-system assessment can assist urban sustainability planning, with comprehensive and consistent comparison of diverse (NBS and conventional) solutions.    

To meet both the Paris Agreement on Climate Change and the UN Sustainable Development Goals (SDGs), nations, sectors, counties and cities need to move towards a sustainable energy system in the next couple of decades. Such energy system transformations will impact water resources to varying extents, depending on the transformation strategy and fuel choices. Sweden is considered to be one of the most advanced countries towards meeting the SDGs. This paper explores the geographical origin of and the current water use associated with the supply of energy in the 21 regional counties of Sweden. These energy-related uses of water represent indirect, but still relevant, impacts for water management and the related SDG on clean water and sanitation (SDG 6). These indirect water impacts are here quantified and compared to reported quantifications of direct local water use, as well as to reported greenhouse gas (GHG) emissions, as one example of other types of environmental impacts of local energy choices in each county. For each county, an accounting model is set up based on data for the local energy use in year 2010, and the specific geographical origins and water use associated with these locally used energy carriers (fuels, heat and electricity) are further estimated and mapped based on data reported in the literature and open databases. Results show that most of the water use associated with the local Swedish energy use occurs outside of Sweden. Counties with large shares of liquid biofuel exhibit the largest associated indirect water use in regions outside of Sweden. This indirect water use for energy supply does not unambiguously correlate with either the local direct water use or the local GHG emissions, although for the latter, there is a tendency towards an inverse relation. Overall, the results imply that actions for mitigation of climate change by local energy choices may significantly affect water resources elsewhere. Swedish counties are thus important examples of localities with large geographic zones of water influence due to their local energy choices, which may compromise water security and the possibility to meet water-related global goals in other world regions.

This paper analyses how local energy and climate actions can affect the use of water and land resources locally, nationally and globally. Each of these resource systems is linked to different Sustainable Development Goals (SDGs); we also explore related SDG interactions. A municipality in Sweden with the ambition of phasing out fossil fuels by year 2030 is used as illustrative case example. The local energy system is modelled in detail and indirect water and land requirements are quantified for three stylised decarbonisation scenarios of pathways to meeting climate and energy requirements (related to SDG13 and SDG7, respectively). Total local, national and global implications are addressed for the use of water and land resources, which relate to SDG6 for water, and SDG2 and SDG15 for land use. We find that the magnitude and location of water and land impacts are largely pathway-dependent. Some scenarios of low carbon energy may impede progress on SDG15, while others may compromise SDG6. Data for the studied resource uses are incoherently reported and have important gaps. As a consequence, the study results are indicative and subject to uncertainty. Still, they highlight the need to recognise that resource use changes targeting one SDG in one locality have local and non-local impacts that may compromise progress other SDGs locally and/or elsewhere in the world.

Water is paramount for the operation of energy systems, for securing food supply and for the industry and municipalities. Intersectoral competition for water resources can negatively affect water scarce regions by e.g. power plants shutdowns, poor agricultural yields, and lack of potable water. Future economic and population growth as well as climate change is likely to exacerbate these patterns. However, models used for energy system management and planning in general do not properly include water availability which can lead to improper representations of water-energy interlinkages. The paper initially highlights the water usage rates of current technologies within electricity generation and technologies with a potential to reduce water usage, electricity consumption or GHG emissions. Secondly, the paper presents currently available data on current and future projected water resources as well as data on energy statistics relevant to water-energy nexus studies. Thirdly, implementation cases are presented showing examples of water-energy nexus studies for the data presented. Finally, the paper highlights main challenges in studying the linkage between water and energy. We find a substantial gap in the general availability and quality of regional and global data for detailed quantitative analyses and also identify a need for standardization of formats and data collection methodologies across data and disciplines. An effort towards a coordinated, and sustained open-access data framework with energy sector water usage at fine spatio-temporal scales alongside hydroclimatic observation and model data using common forcings and scenarios for future projections (of climate, socio-economy and technology) is therefore recommended for future water-energy nexus studies.

Cities are vital for achieving the Sustainable Development Goals (SDG), but different local strategies to advance on the same SDG may cause different ‘spillovers’ elsewhere. Research efforts that support governance of such spillovers are urgently needed to empower ambitious cities to ‘account globally’ when acting locally on SDG implementation strategies.

The authors regret two instances of misinterpretation of input data and one formatting error in the previously published paper as titled above. First, the numerical estimates for water use in NYC electricity and natural gas supply were found to be incorrect due to a conversion error in a data file. This error has now been corrected and the estimates have been changed to correctly correspond to the references on which they are based on. These changes have led to a recalculation of indirect water use reduction potentials in the interventions studied in the paper. Second, two errors due to primary data misinterpretation related to the studied green roof intervention have been found and corrected. The first led to an overestimation of the green roofs’ energy use reduction potential in the previously published paper. The second led to an underestimation of their installation cost. These errors have also been corrected and all numerical results for the green roof intervention have been recalculated. In the updated sections 3 and 4 of the original publication (below), Table 2, Table 3, Fig. 2 and Fig. 3 are updated with the new results related to both indirect water use reductions and green roof performance and costs. The text in the below sections have been given minor adjustments to clarify this update. These changes make green roofs a less economically favourable intervention in comparison to the previously published results. It also makes indirect water use reductions relatively smaller compared to direct water use reductions. All other results as well as the conclusions of this paper are still valid and unchanged. Lastly, a typo in writing of Eq. (7) in the manuscript text has been corrected. There was no error in the equation used in the analysis; hence, no numerical results have been effected by this correction. The authors would like to apologise for any inconvenience caused. Corrected writing of Eq. (7), section 2.3.1: [Formula presented] Updated sections of the original publication.

In the referenced article, Engström R, et al. (2018), the authors would like to report a calculation error. Correcting this error does not alter any of the overarching results or conclusions of the article, but changes the results in the original Table 3 and Figure 3. Two typographical errors were also found in the main article, and are corrected here. The supplementary material has also been updated to reflect these corrections.