Abstract
Water footprinting has revealed hydro-economic interdependencies between distant global geographies via trade, especially of agricultural and manufactured goods. However, for metropolitan areas, trade not only entails commodity flows at many scales from intra-municipal to global, but also substantial intra-metropolitan flows of the skilled labor that is essential to a city’s high-value economy. Virtual water flows between municipalities are directly relevant for municipal water supply policy and infrastructure investment because they quantify the hydro-economic dependency between neighboring municipalities. These municipalities share a physical water supply and also place demands on their neighbors’ water supplies by outsourcing labor and commodity production outside the municipal and water supply system boundary to the metropolitan area. Metropolitan area communities span dense urban cores to fringe agricultural towns, spanning a wide range of the US hydro-economy. This study quantifies water footprints and virtual water flows of the complete economy of the Phoenix Metropolitan Area’s municipalities. A novel approach utilized journey to work data to estimate virtual water flows embedded in labor. Commodities dominate virtual water flows at all scales of analysis, however labor is shown to be important for intra-metropolitan virtual water flows. This is the first detailed water footprint analysis of Phoenix, an important city in a water-scarce region. This study establishes a hydro-economic typology for communities to define several niche roles and decision making points of view. This study’s findings can be used to classify communities with respect to their relative roles, and to benchmark future improvements in water sustainability for all types of communities. More importantly, these findings motivate cooperative approaches to intra-metropolitan water supply policy that recognize the hydro-economic interdependence of these municipalities and their shared interest in ensuring a sustainable and resilient hydro-economy for all members of the metropolitan area.
Highlights
Cities are hotspots of global environmental change and economic consumption [1,2]
Phoenix and Scottsdale, core Phoenix metropolitan area (PMA) municipalities, had the largest net virtual water inflows associated with labor, while Surprise and other suburban “bedroom” municipalities, had the largest net virtual water outflows associated with labor
36% of virtual water inflows embedded in the labor market resulted from intra-metropolitan area flows; the remaining 64% resulted from circular virtual water flows within each municipality
Summary
Cities are hotspots of global environmental change and economic consumption [1,2]. Groups of co-located cities form metropolitan areas contain varying types of land uses that range from preserved natural lands; to rural and agricultural land uses; to highly urbanized forms, which are major hubs in the world city network [3,4,5]. While direct water sharing agreements and water policies reflect formal long-term legal and political agreements, virtual water flows reflect short-term voluntary economic conditions, such as competitive and locational advantages Both the long-term legal agreements about “real” physical water resources, and the short-term trade agreements that imply virtual water cooperation and virtual water transfers, have hydro-economic impacts on these communities such as added or avoided water infrastructure, investment, and operating costs, or economic opportunities. In order to inform cooperation at the municipal scale on water supply and infrastructure policy, we contextualize virtual water flows with respect to the size of each municipality’s physical water supply infrastructure; in other words, we relate the virtual water flow to the urban water metabolism This will demonstrate how much larger (or smaller) each municipality’s physical infrastructure and water right would need to be if not for intra-metropolitan virtual water connections with trading partners that share the local physical water supply
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