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Smart Growth programs—developing urban areas with a variety of building types and land uses in a concentrated space—are touted for their potential to spur economic development through the creation of more attractive, environmentally sustainable, and walkable communities. One underlying theme is that increased urban density allows people to access a variety of shops, housing options, and recreational areas without having to hop in their cars. The most commonly cited potential benefits of smart growth include improved public health, higher air quality due to reduced vehicle traffic, more efficient use of land, protection of valued natural or open spaces from sprawl, increased property values because of high demand, and often greater community involvement in the development process.

A recent post on the School of Government’s Community and Economic Development blog outlined some examples of Smart Growth programs here in North Carolina, and Glenn Barnes earlier wrote about five ‘tools’ included in the EPA’s Building Blocks for Sustainable Communities program. This post examines what I think is a sometimes overlooked benefit of Smart Growth and higher densities: water conservation.

The primary mechanism for water savings from densification is a reduction in outdoor water use, especially irrigation. Here in North Carolina, outdoor use has been estimated to account for an average of 20 to 30 percent of total water used in a given facility, and can peak to as much as 70 percent in the summer growing season. Nationwide, landscape irrigation accounts for nearly one-third of all residential water use, but there are substantial variations according to local climates. Overall, the connection between urban density and water conservation is fairly straightforward: If residents have fewer—or just smaller—lawns, then cities can achieve meaningful reductions in total water use. Considering that between 5 and 20 percent of residential customers in communities in NC apparently use irrigation systems to water their lawns, densification and reductions in lawn sizes could have a significant effect on water use behavior for many residents.

Recent research has provided a variety of estimates for the scale of these density-driven reductions. In a 2013 article in Landscape and Urban Planning, Runfola et al. used a combination of land cover analysis and monthly water use data to examine water use in Ipswich, MA. The researchers then projected total residential water use under two different future growth patterns: (1) Standard suburban development based on current trends; and, (2) Smart Growth with higher residential densities. The Smart Growth scenario yielded a 5 percent reduction over time without the use of additional demand side management programs. Another study by Nahlik and Chester compared water use projections under similar standard and Smart Growth scenarios for Phoenix, AZ. In that case, researchers estimated residential water savings of approximately 37 percent over time. The findings in these studies not only reflect the potential water conservation benefits of Smart Growth, but also illustrate that these benefits may be larger in hotter, drier climates.

One potential downside of densification is the development of Urban Heat Islands. In general, Urban Heat Islands are locations in urbanized areas with elevated temperatures caused by higher heat absorption rates and lower heat release rates in urban versions of natural environments. The resulting increase in temperatures can then cause residents to use more water. In a 2007 study again focused on Phoenix, AZ, Guhathakurta and Gober estimated that a one degree increase in an area’s daily low temperature can increase monthly water use in single family units by approximately 1.7 percent. This effect is smaller than estimates for potential water savings from Smart Growth, but it may be worth investigating mitigation strategies to combat the development of Urban Heat Islands. Doing so would not only help ensure water savings, but also contribute to the other goals of Smart Growth by making the urban environment more pleasant for residents and visitors alike.

Water conservation, in turn, has significant effects on utility finance. In the short term, under current water rate structures, conservation would reduce the revenues collected from variable charges, which make up the majority of revenues from customers (note: there are strategies and alternative water rate structures that could significantly improve the resiliency of revenues to reductions in demand). However, in the long term, conservation and denser urban development patterns could ultimately lower costs by deferring or limiting expensive expansions of the water system. A 2013 study by the Alliance for Water Efficiency found that the City of Westminster in Colorado had lower water rate increases as a result of conservation than the rate increases would have been in the absence of conservation. Smart growth, by accelerating water conservation, could help the community save on additional capital costs while managing its water resources.

Trey Talley is pursuing a Master’s of City and Regional Planning at the University of North Carolina Chapel Hill, and he currently serves as a research assistant for the Environmental Finance Center.

References:

Guhathakurta, Subhraji and Patricia Gober. 2007. “The Impact of the Phoenix Urban Heat Island on Residential Water Use” Journal of the American Planning association, 73:3, 317-329. DOI: 10.1080/01944360708977980

Nahlik, Matthew J. and Mikhail V. Chester. 2014. The Water, Energy, and Infrastructure Co-Benefits of Smart Growth Planning in Phoenix, Arizona. Working paper no. SSEBE-CESEM-2014-CPR-001. Center for Earth Systems Engineering and Management, Arizona State University, 2014. https://repository.asu.edu/attachments/134588/content/asu-cobenefits-phoenix-smart-growth.pdf.

N.C. Division of Pollution Prevention and Environmental Assistance. 2009. Water Efficiency: Water Management Options. http://www.savewaternc.org/Documents/WaterEfficiencyLandscaping.pdf.

Runfola et al. 2013. A growing concern? Examining the Influence of Lawn Size on Residential Water Use in Suburban Boston, MA, USA. Landscape and Urban Planning 119 : 113-23.

U.S. Environmental Protection Agency. 2013. Reduce Your Outdoor Water Use. https://www3.epa.gov/watersense/docs/factsheet_outdoor_water_use_508.pdf.

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