Environmental and Management Constraints Drive Urban Water Security at the Water-Energy-Land Nexus

The impacts of climate change, land-use intensification, and population growth put increasing pressure on the maintenance of critical urban services, including water, energy, and food supply. Constraints in land and water availability, the choice of energy sources and governance strategies lead to imbalances between supply and demand in space and time. Here, we propose a new analysis approach that highlights the different roles of supply- and demand-management for the variability of urban water services. We investigate urban water governance strategies for 50 cities worldwide considering water availability, supply efficacy, and demand, as well as transfer distances for water imports, and, for a subset of cities, energy sources (renewable/non-renewable) and intensity for water supply. Our results allow distinguishing cities with sparse versus profligate water use and grouping them into different categories characterized by varying levels of urban water supply (in-)security, and demand management strategies. Temporal and spatial variability in water availability and supply, respectively, demonstrate the hydro-climatic and management constraints in these cities. We discuss the urban water management of three contrasting cities in the context of the water-energy-land nexus: Singapore, Mexico City, and São Paulo. Temporal hydro-climatic variability and the (un-)availability of land drives the strategies of water management in these cities, which in turn drive the energy intensity of the water sector. These insights are relevant for understanding inter-urban variability of urban water supply, and security-sustainability tradeoffs in the water-energy-land nexus resulting from the choice of and constraints in management options.