With the constant increase of population and urbanization worldwide, stress on water, energy, and food resources is growing. Climate change constitutes a source of vulnerability, raising the importance of implementing actions to mitigate it. Within this, the water and wastewater sector represents an important source of greenhouse gas (GHG) emissions, during both the construction and operation phase. The scope of this study is to analyze the GHG emissions from the current and future water supply scheme, as well as to draw a comparison between possible water reclamation with resource recovery scenarios in the town Leh in India: a centralized scheme, a partly centralized combined with a decentralized scheme, and a household level approach. Precise values of emission factors, based on the IPCC Guidelines for National Greenhouse Gas Inventories, previous studies, and Ecoinvent database, have been adopted to quantify the different emissions. Potential sources of reduction of GHG emissions through sludge and biogas utilization have been identified and quantified to seize their ability to mitigate the carbon footprint of the water and wastewater sector. The results show that the future water supply scheme will lead to a significant increase of the GHG emissions during its operation. Further, it is shown that decentralizing wastewater management in Leh town has the least carbon footprint during both construction and operation phases. These results have implications for cities worldwide.

Climate-resilient water safety plans (CR-WSPs) have been developed as a risk-based approach to ensure a safe drinking-water supply while addressing the increasing stress on water resources resulting from climate change. Current examples of the application of CR-WSPs show a strong sectoral approach that fails to explore the potential synergies between other climate-sensitive sectors related to water, such as food and energy. This can increase the vulnerability or decrease the overall resilience of urban systems when planning climate change adaptation measures. In this work, the Water–Energy–Food (WEF) Nexus approach was applied in the formulation of a CR-WSP in Leh Town, India, a city with rapid development and population growth located in the Himalayas—one of the most sensitive ecosystems to climate change. The WEF Nexus approach was applied in the system description using a critical infrastructure approach and in the formulation of scenarios for risk management which exploited intersectoral synergies through water reclamation with resource recovery using constructed wetlands. The improvements in WEF security and risk reduction were demonstrated through indicators and risk mapping with geographical information systems (GISs). The methods for integrating the WEF Nexus approach in CR-WSPs provided through this work can serve as a base for a trans-sectoral, resilient approach within risk-based approaches for water security.

Urbanization has created some of the world's greatest development challenges. At the same time, cities present an opportunity to tackle these challenges comprehensively. For this, an integrated urban development approach is needed. The Water-Energy-Food (WEF) Nexus approach offers cities an integrated urban planning framework to devise sustainability pathways. However, so far there exist no comprehensive guidelines to aid municipal government decision-making on how to apply the Nexus approach in an urban context. This paper highlights the origins of the WEF Nexus approach within the integrated urban planning discourse. It explains the method to introduce Nexus with special emphasis on Nexus training supporting the implementation of the Nexus approach. The “Urban Nexus Development Cycle” as part of the Nexus training, guiding urban practitioners to overcome “silo thinking” is the innovative element as well as the pro-active involvement of universities in the Nexus process.

Avocados, which have been labeled a superfood and are very popular around the world, are often grown in areas with water scarcity and have long-distance transports to their end consumer. Water and carbon footprints could be reduced by using greenhouse farming, waste heat and rainwater. This study aims to determine whether avocados and other exotic fruits could be locally or regionally grown in greenhouse systems in Bavaria heated using waste heat and examines whether this approach decreases the resulting water and carbon footprints. To test these hypotheses, the waste heat potential is estimated by analyzing a database provided by the Bavarian Environment Agency. Data on water and carbon footprints are extracted from databases by The Water Footprint Network and FAOSTAT. As a local case study, a greenhouse system using waste heat of a nearby glass factory in Upper Franconia is considered. The results show a tremendous waste heat potential for Bavaria and Munich with reduced carbon, but similar water footprints compared to international avocado production. The required area for these avocado farms would only amount to 0.016% of Bavaria's or 0.02% of Munich's total area. With more uncomplicated handling and earlier fruit bearing, fruits like papaya, guava, or carambola seem to be better suited for greenhouse farming than avocados. Waste heat supported farming in controlled environments can require significantly less water through modern irrigation techniques and should be considered when designing new food security concepts for urban or rural areas.

With the rapid expansion of cities due to population growth and urbanization, conventional centralized wastewater collection and treatment systems are slowly becoming a burden; expensive maintenance is required for aging plants and piping infrastructure, the cost of expanding the capacity to cover demand from population growth, and new regulations for tighter control over certain pollutants such as micropollutants. As an alternative to this system, this study discusses the feasibility of decentralized treatment systems at the neighborhood scale. Taking a Water-Energy-Food (WEF) Nexus approach, such systems can support water and energy conservation, recovery of water, energy, and nutrients as well as generation of energy from wastewater, be customized to individual water and energy requirements, and eliminate the need for lengthy pipe networks. The method employed in this study is comparing the economic feasibility of the status quo to a proposed decentralized solution. The study finds that the costs of implementing a hypothetical decentralized water reclamation with an integrated resource recovery system using an anaerobic membrane bioreactor (AnMBR) in a downtown high-density neighborhood of the city of Munich, Germany, can theoretically be recuperated within two years. This alternative system may cost 60% of what it costs to run the centralized system. By linking the AnMBR to a biogas digestor and using systematically harvested organic waste as a co-substrate, the decentralized system can generate enough energy to run itself and even feed some energy to the grid. This study is highly hypothetical, yet generating evidence such as this can support a systemic socio-technical transition towards a more circular economy with optimal resource recovery.