The economic value of local water supplies in Los Angeles

Abstract

In western North America, massive infrastructure systems convey water over hundreds of miles to support cities, farms and economic growth. The systems were twentieth-century solutions to seasonal water scarcity, but today imported water supplies are strained. Cities are looking to water conservation and local sources of supply as future solutions. But integrated planning remains a challenge. Here, we assess economic implications of transitioning to local water supply reliance. We enhance an integrated model (Artes) of urban water management in Los Angeles County (LA County) with annualized costs for water supply sources (local and imported) and water conservation. We model cost-effective options for mitigating the effects of imported water cuts affecting nine million people within a hundred agencies, and denote associated policy options. The approach allows for a more holistic assessment that improves upon current studies, which typically compare nominal and annualized prices of different options. The concept of urban water supply trains, which include the multiple steps of acquiring, treating, distributing, and discharging or reusing water, is presented to understand emerging cycles of water supply. The analysis enhances current studies that often emphasize single agency perspectives, but also shows how existing assumptions and infrastructure shape what appear to be cost-effective options.Systematic studies of urban water management necessarily include many aspects of operations [1][2][3][4] . Engineered pipe and channel networks move surface water and runoff. Water supply utilities build and maintain systems to keep taps running. Complex networks of agencies oversee the acquisition, distribution and use of urban water and wastewater 5,6 . Landscapes and outdoor water use are especially important drivers of water demand in California, as half of urban water use goes to irrigation and trees [7][8][9][10] . Economics and social attitudes shape the expectations of residents and utilities for water supply. In many cities across the globe, climate change and population growth will test operating assumptions in the current systems 11 .Los Angeles County is an immense laboratory for exploring the future of urban water in seasonally dry climates (Fig. 1). The county currently receives 55-60% of its annual water supplies from imported sources, which include northern California through the Sacramento-San Joaquin Delta, the Colorado River basin, and the higher-altitude Owens Valley. The remainder comes from local sources, including groundwater pumping, recycled water (nonpotable or indirect recharge) and stormwater capture 5,12,13 . Of the water imported to southern California by the giant Metropolitan Water District of Southern California (MWD), Los Angeles County agencies receive approximately 40%. The City of Los Angeles receives additional imports from the Owens Valley. A shift to becoming primarily reliant on local sources is significant in a region famous for its efforts to import water [14][15][16] .Previously, to u...

Energy use for urban water management by utilities and households in Los Angeles

“…It includes 25 years of calibrated monthly rainfall and runoff estimates. The model has previously been used to assess multiple aspects of water supply and demand management in the region (Porse et al 2018a, 2018b, Pincetl et al 2019. A full description of the formulation, data, and assumptions used in developing the model are available in previous studies and the Supporting Information for this article.…”

“…The dollar value is equal to the weighted sum of flows, based on the flow volume between two points in the network and the specified unit cost. The economic value of losses associated with each water supplier is assessed using a demand function procedure with estimated water prices and elasticities of demand derived from existing sources (Jenkins et al 2003, Buck et al 2016, Porse et al 2018b. The model formulation includes constraints that emphasize minimum deliveries of water to districts for health and safety (in-home residential) and commercial and industrial needs.…”

“…The minimum volume of residential water demands in the modeled scenarios, evaluated as the volume of water needed to supply health needs for in-home indoor uses, was estimated to be 1,014 million liters per day (268 million gallons per day) based on a 189 lpd (50 gpd) standard. The method for calculating this amount is described in previous research (Porse et al 2018b).…”

“…Two questions are important. First, what is the energy intensity of existing and alternative urban water supply operations that characterize the multi-step procedures for acquiring, conveying, treating and distributing water and sewage throughout a system (Mo et al 2014, Porse et al 2018b? Second, in case study cities, what are the relative contributions of utility and end-use energy consumption for water management in cities across diverse climate and geographic regions?…”

“…In addition, we evaluate opportunities to reduce system-wide energy use for water management through better use of alternative supply sources such as stormwater capture and water reuse. We quantify the electricity intensity (EI) of various urban water 'supply trains' (Porse et al 2018b), including a novel approach for estimating distribution energy within a local urban water supply pipe network. The methods and results are widely relevant for regional and national policies focused on the important task of reducing energy use and associated greenhouse gas emissions of urban water systems.…”