City sustainable transitions – Modelling integrated urban water and energy system optimal pathways

Urban areas constitute over three-fourths of the current global economy, house more than half of the global population and consume more than two thirds of final global energy consumption with the consequential greenhouse gas... [ view full abstract ]

Urban areas constitute over three-fourths of the current global economy, house more than half of the global population and consume more than two thirds of final global energy consumption with the consequential greenhouse gas emissions. Urban areas have a strong role on providing basic wellbeing of the population: unpolluted air, clean water, sanitation, work, health care, and at the same time reduce the environmental impact of their activities. Urban areas also concentrate population water demands, which stress finite supplies of available freshwater. Current and future factors such as climate change and rapid urbanization poses additional risks to cities functional capacity. The New Urban Agenda of Habitat III shows the importance of cities in the creation of world sustainable future. This new dynamic is converting cities to become vectors of sustainable development. Cities have started the deployment of response mechanisms through initiatives like Covenant of Mayors. Although, these are silo (in this case climate change mitigation) not including other related key resources and services consumed at cities that cause internal and external environmental degradation (e.g. water consumption). Both urban energy and water systems are complex and highly interlinked, posing additional challenges in the definition of cities sustainable pathways. There is a necessity of holistic approaches and tools to support the design adequate integrated measures. It was developed an urban energy and water systems optimization tool covering all their chain and linkages: from energy and water supply sectors and sources (e.g. electricity production and water capture) to end use sectors (e.g. residential) and wastewater production and final treatment. This tool is an upgrade of a city scale energy system technology-rich optimization TIMES model to include the urban water system, considering all the phases of this systems (e.g. water abstraction and pumping, water treatment and distribution and consumption). The model embraces the water services at household scale. It was applied to major city in Portugal as a case study and cover a time scale from 2013 to 2030. Three different scenarios were developed in order to: 1) asses the effects of city energy system decarbonization in the adoption of more energy efficient technologies in the urban water system (CITY_GHGTargetscenario) 2) assess the impacts of water resource scarcity (Wat_ScarceScenario) and also 2) high water costs (Wat_CostScenario) in the adoption of more water and energy efficient end use technologies. The results show that the GHG emission city target favour the adoption of energy efficient technologies with higher emission reduction in 2030 (e.g. EVs). The scenarios water targeted (scarcity and cost) induce the introduction of more water efficient technologies and also an energy consumption reduction in the water extraction and distribution pahses. A implementation of this model show a range of cost-effective solutions to low carbon urban energy system transition and the capacity to improve efficiency of specific urban water system phases. The results show the co-impacts of deep cities decarbonization pathways links with other city resources consumption, stimulating new research on the climate change-energy-water nexus related topics.