Applied Energy

Cities have evolved as centers of economic growth and often described as open systems where the intake of resources is heavily dependent on flows imported from the external environment. The question is, how much of the resource available in cities is effectively utilized? In response, this paper develops an ecological-thermodynamic approach to assess the ability of a system to make full use of the resources available and reduce the demand for new resources. In this work, open system network effectiveness analysis is introduced as a novel assessment method to investigate the cities’ producer and consumer behaviors by studying the resource flow connections and the interactions between the socio-economic sectors. Investigation on the urban flows network evaluates the ability of the system to utilize the resource imported through the effectiveness of utilization indicator and the ability to convert the resource imported to useful products through the effectiveness of conversion indicator. The effectiveness indicators, utilization and conversion, represent the consumption and production characteristics of the system respectively. This is tested through a case study conducted for Singapore city over the time period 2005–2014. The effectiveness results show that the city, on average, has utilized 45% of the maximum extractable usefulness from the resources imported throughout the years, with the lowest effectiveness, 39%, and the highest effectiveness, 50%, in the years 2007 and 2014 respectively. The trajectory of effectiveness results throughout the years suggests a trade-off relationship between the producers and consumers to balance the production and consumption of resources in the city.

Over the past decade, analyzing issues within the ‘water-energy nexus’ has become a topic of increasing attention for the scientific and policy communities. Based on an extensive survey of recent scientific literature on the water-energy nexus, 70 studies were identified and 35 were selected as comprehensive case studies for review. The reviewed studies were classified and assessed according to groupings based on both geographic scale and their ‘nexus scope’. In addition to providing a depository summary of a wide range of current existing methods and tools for water-energy nexus analysis, the paper discusses these approaches based on their main purposes. From this review, it is clear that the research on water-energy nexus has seen a significant increase in both the number of studies and the capacity of the scientific community to productively assess water and energy interlinkages at a higher resolution. At the same time, this review has also concluded that, while many studies aim to develop new methods and frameworks to comprehensively assess interactions between water, energy and other elements, none can or do provide a singular framework for performing a “nexus study”. Furthermore, many researches are at the “understanding” stage with an emphasis on the quantitative analysis of the water-energy nexus. Fewer approaches are designed to support governance and implementation of technical solutions, and this is considered to a priority challenge area for the scientific community if it aims to achieve greater impact on resource policy and management. There is a clear need to improve our ability to classify and compare the capacities, strengths and weaknesses between existing approaches. This would better enable a wider group of stakeholders to utilize existing knowledge to improve their effective management of water and energy resources. It could also help focus the scientific community to more effectively improve upon the existing knowledge base and to increase focus on “governing” and “implementing” the nexus.

Cities are leading actions against climate change through global networks. More than 360 global cities announced during the 2015 Paris Climate Conference that the collective impact of their commitments will deliver over half of the world's urban greenhouse gas emissions reductions by 2020. Previous studies on multi-city carbon footprint networks using sub-national, multi-region input-output (MRIO) modelling have identified additional opportunities for addressing the negative impacts of climate change through joint actions between cities within a country. However, similar links between city carbon footprints have not yet been studied across countries. In this study we focus on inter-city and inter-country carbon flows between two trading partners in a first attempt to address this gap. We construct a multi-scale, global MRIO model to describe a transnational city carbon footprint network among five Chinese megacities and the five largest Australian capital cities. First, we quantify city carbon footprints by sectors and regions. Based on the carbon map concept we show how local emissions reductions influence other regions' carbon footprints. We then present a city emissions 'outsourcing hierarchy' based on the balance of emissions embodied in intercity and international trade. The differences between cities and their position in the hierarchy emphasize the need for a bespoke treatment of their responsibilities towards climate change mitigation. Finally, we evaluate and discuss the potentially significant benefits of harmonising and aligning China's carbon trading schemes with Australia's cap and trade policy.