Methodologies for Analyzing the Water Footprint of Cities

Abstract:

Cities are hotspots of commodity consumption and trade, which impacts distant water resources. Water flows virtually into cities through this commodity exchange and thus local water issues can be globally linked. This form of water ‘teleconnection’ is being increasingly recognized as an important aspect of water decision making at the national scale. In cities and urban areas, the inflows and outflows associated with virtual water flows are rarely acknowledged. The emphasis is on the physical and engineered water balances. Our aim is to show the need to account for virtual flows in population-dense regions to better inform local water decision makers. We compare and contrast current methods to assess virtual water. Specifically, we examine the Water Footprint Network method, life cycle assessment, multi-regional input-output method and embedded resource accounting. We build upon these approaches and suggest a framework to account for virtual flows in US cities in the context of constrained available datasets. Results highlight the potential for making estimates of virtual flows in cities more routine and address how this could fit within an urban metabolism framework. We discuss how this framework can assist decision makers as we move into a new era of understanding the role of cities in the context of water scarcity.