Paper From Water - MDPI: 'Decoupling Urban Water Use and Growth in Response to Water Scarcity'

Just received notification of this fascinating paper from MDPI's Water: 'Decoupling Urban Water Use and Growth in Response to Water Scarcity' by Brian Richter, Kendall Benoit, Jesse Dugan, Gabriella Getacho, Natalie LaRoe, Bailey Moro, Tyler Rynne, Maria Tahamtani, and Allen Townsend. Water 2020, 12(10), 2868; https://doi.org/10.3390/w12102868

Brian Richter is the former freshwater guru for The Nature Conservancy. I use his book Chasing Water in several of my classes.

Here is a PDF: Download Water-12-02868

To read the paper online, click here. For a news story of the paper click here.

I've pasted the Abstract and Introduction below.

Abstract
Many cities in the western US face difficult challenges in trying to secure water supplies for rapidly growing urban populations in the context of intensifying water scarcity. We obtained annual data from urban water utilities across the western US to document trends in their water usage and service populations. We found that many cities have been able to accommodate population increases while simultaneously reducing their volume of water use, thereby decoupling growth from water use. This outcome is largely attributable to reductions in per-capita residential use. We identify additional untapped potential that can sustain and widen this decoupling for many cities.

1. Introduction
Access to additional water supplies has been a prerequisite for population and economic growth throughout human history. When early Roman towns outgrew their local water supplies, they engineered aqueducts to bring water from distant springs. Two thousand years later, the City of Los Angeles, California, built a 674-km aqueduct from the Sierra Nevada Mountains that unleashed a ten-fold population increase in the first half of the 20th Century. Other engineering advancements throughout the past century enabled the construction of massive storage reservoirs and wells tapping groundwater hundreds of meters deep, facilitating the growth of modern mega-cities, industries, and extensive irrigated farming regions.

 

It is therefore unsurprising that many urban planners and political leaders continue to assume that growing populations and economies will require ever-more water. Abraham and others [1] found that future demand projections by the ten largest water utilities in the State of California overestimated future demands 98% of the time, with projections that proved to be 23–26% too high even when the forecast length was only five years. The authors attributed these over-projections primarily to underestimation of the rate by which cities were reducing their per-capita usage.

 

Similarly, when the US Bureau of Reclamation in 2012 projected multi-decadal future water demands from the Colorado River of the western US, it assumed that the population-following trend of increasing water use over the past 90 years would largely continue throughout the next 50 years (Figure 1) [2]. Based on a suite of planning scenarios ranging from slow (+23%) to rapid (+93%) population growth, the Bureau projected increased water demands of 27%–49% by 2060. These projected increases in demands were based almost entirely on expected increases in municipal and industrial water needs due to population growth [2].

 

Figure 1. Historical traces of available water and actual use shown here refer to the natural supply of surface water from the Colorado River and the consumptive use of that water over time. The Colorado River Basin Water Supply and Demand Study conducted by the US Bureau of Reclamation in 2012 included water demand forecasts through 2060, based upon scenarios ranging from slow to rapid population growth [2]. It is now evident that this demand forecasting did not adequately account for recent downward trends in water consumption (historical estimates of available water and total consumptive use from US Bureau of Reclamation [3]).

However, the Bureau’s projected water demands for 2015—based primarily on forecasts from each of the seven states sharing Colorado River water—proved to be ~20% too high, even though the forecast was published only three years earlier (Figure 1). Water consumption in the basin has not increased as projected, but has instead dropped by 16% from 2000−2015 (Figure 1) [3]. The Bureau’s water planners and their state-agency peers participating in the 2012 study inadequately recognized the strength of downward trends in per-capita municipal water use during recent decades. As reported later in this paper, the nine cities we surveyed that source water supplies from the Colorado River basin lowered their per-capita use by 19–48% during 2000–2015.

 

As discussed in greater detail below, we conducted a survey of water utility managers in 20 western US cities. In our discussions with water utility staff about their motivations for implementing water conservation strategies, water scarcity and the difficulty or expense of securing additional water supplies for their growing populations were universally expressed as leading motivations. As an example, Figure 1 illustrates the fact that during recent decades, consumptive water use in the Colorado River basin has exceeded total river flow in most years since the early 1990s, enabled by progressively depleting large storage reservoirs in the basin [3].

 

In recent years, various agencies have suggested that as water scarcity expands and intensifies globally, a decoupling of water use from growth will be essential in sustaining economic growth and well-being [4]. In 2016, the United Nations Environment Programme (UNEP) warned that “half the world faces severe water stress by 2030 unless water use is ‘decoupled’ from economic growth” [4]. At the global level, economic decoupling appears to be well underway, as the global economy grew at a rate five times that of global water consumption during the past century [4].

A similar trend of decoupling has been observed in the US. After reaching a zenith in 1980, total US water use had dropped by 27% by 2015, even while the country’s population grew by 42% and GDP expanded more than six-fold [5,6]. During 2000–2015, the period of focus in this paper, substantial reductions in water use were observed in each major water-use category: Irrigation (−55%), Public Water Supply (−45%), Industrial (−40%), and Thermoelectric Power (−30%).

 

However, as UNEP asserts [4], the need and potential for decoupling is most appropriately assessed at local or regional scales; such local assessment can reveal the benefit of decoupling strategies on stressed water sources. This is exemplified by research into water decoupling efforts in China. Of 31 provinces in China, over 60% displayed strong decoupling between water consumption and economic growth after 2011, the year that China began to place a deliberate urgency on environmental protection efforts [7]. The Yellow River—the country’s second largest river basin—has been identified as a water-risk hotspot by the World Resources Institute [8]. Within this basin, the Beijing–Tianjen–Heibei region exhibited strong decoupling between water consumption and economic growth from 2004–2017, which was attributed to improved water-use efficiencies and conservation awareness on an individual scale, as researchers documented a substantial decline in the annual per-capita water footprint over this period [9]. Similarly, in a comparative urban review of China’s three largest megacities for the period 2005–2015, Guangzhou was found to display the strongest decoupling between economic growth and water usage, followed by Shanghai and Beijing.

 

In this study, we sought to better understand the policy drivers and incentives that have enabled decoupling between urban growth (measured by both population size and by gross domestic product or GDP) and water demands, through an examination of recent trends in western US cities.

 

Cutting to the chase....

6. Looking Forward

Great progress has been made in reducing urban water use in recent decades. The cities surveyed in our analysis document the fact that substantial increases in service populations can be accommodated without increasing total water use. Key to this decoupling has been their ability to push down per-capita water use at a rate greater than the demands associated with adding newcomers into their service populations.

 

There appears to be much room for continued improvement within cities that have not yet attained the high levels of performance we document here, as well as within cities that are already engaged in water conservation. DeOreo and others [18] project that residential indoor use in the US will drop by another 37% in coming years due to the fact that less than half of American homes have installed highly efficient toilets or clothes washers, two of the greatest uses of water indoors. By comparison, 86% of Australian homes now have high-efficiency toilets [39]. Leak reduction has the potential to save an additional 14% of water use in homes, on average [18]. This suggests that total indoor water use in American homes could potentially drop by at least another 50% in coming years.

 

DeOreo and others [18] also suggest that outdoor water use could be further reduced by 16% by eliminating excessive watering practices. We add that capturing rainwater for use outdoors holds great promise for alleviating pressure on freshwater supplies. Cahill and Lund [39] documented that more than 40% of Australian households are using rainwater storage tanks, whereas they are used by only a tiny fraction of American homeowners and businesses.

 

We also see great potential in the use of alternative water sources—wastewater reuse, large-scale stormwater capture, desalination, and even condensate capture from heating, ventilation, and air conditioning (HVAC) systems—as an important strategy for reducing freshwater extractions in water-stressed areas [40]. One bellwether is the City of Los Angeles’ commitment to recycle 100% of its wastewater by 2035, at which time recycled water will be providing 35% of the city’s supply as compared to only 2% today [41]. Another important factor will be the increased frequency and volume of voluntary, compensated transfers of water conserved on irrigated farms to meet urban needs, a very cost-effective strategy in regions with large acreage of irrigated farms [42,43,44].

 

We note that the challenge of holding the line on total water use appears more difficult for larger cities or utilities with very high rates of population increase, simply because per-capita use must drop by a greater extent to keep total volume constant. All but one of the cities in our survey were able to attain total volume reductions during 2000–2015 (the San Antonio Water System experienced an increase of 21% in its total water use over this period). This utility experienced extreme growth (56%) in its service population during this period, which resulted from both population growth and a merger with another water provider, and it had already substantially reduced its per-capita water use prior to 2000.

 

For cities across the US, water conservation and the use of alternative water sources will both continue to offer tremendous potential for accommodating population growth without placing further pressure on stressed freshwater supplies in the coming decades [42]. More than half of all US counties were already able to do this during 2000–2015 [10]. The challenge for urban water managers will be to fully harvest the potential for water savings that can help constrain their needs within the limits of available water supplies.

Enjoy!

 

"Despotism corrupts the person who submits to it far more than the person who imposes it." - Alexis de Tocqueville, quoted in the @washingtonpost via @TheWeek