KEEPING YOUR COOL: MANAGING HEAT IN OUR CITIES
With an increased emphasis on conservation, the first target is often outside irrigation use. There are many cases of over watering, allowing water to pool or run off the irrigated areas, irrigating during peak evaporation periods or other water wasting practices. For a utility, outside irrigation use is a low hanging fruit—customers can take to action to reduce consumption without really having to change their personal habits.
And there is a great opportunity to avoid waste and save water. The United States Environmental Protection Agency estimates that more than 50 percent of water use in residential areas is used for outdoor purposes. In dry climate areas like the Southwest, that usage can top 60 percent. Nationwide, average outdoor water use is estimated at 9 billion gallons per day.1
However, there are good reasons to maintain outdoor greenspaces—even in drought—provided that the water use can be optimized to avoid wastage.
NO MAN IS AN ISLAND — EXCEPT FOR HEAT ISLANDS
It’s well known that the trappings of an urban environment—concrete, brick, asphalt, cement and other infrastructure that disrupt the natural cooling effect of vegetation—results in an increase the daytime temperatures in cities. This temperature increase of 1.8° to 5.4° F (1° to 3° C)2 can extend well into the nighttime hours and results in increased demand for power to operate air conditioning units, localized disruption of weather patterns (including precipitation), and an overall decline in quality of life for residents.
Interestingly, suburban areas around desert cities are actually cooler than both the city center and the outer rural areas because the irrigation of lawns and small farms leads to more moisture in the air from plants that would not naturally grow in the region.
“If you build a city in an area that is naturally forested—such as Atlanta or Baltimore—you are making a much deeper alteration of the ecosystem,” said Marc Imhoff, biologist and remote sensing specialist at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center in Greenbelt, Maryland. “In semi-arid areas with less vegetation—like Las Vegas or Phoenix—you are making less of a change in the energy balance of the landscape.”3
A recent NASA study provides one of the first assessments of how the type of vegetation impacts the accumulation and dissipation of heat energy in a city. It also identified a “tipping point” with respect to the urban environment: as the impervious surface area (ISA) increases beyond about 35%, the heat impact begins to increase sharply.4
IF A TREE FALLS IN THE FOREST…
The message is clear: our urban environment needs greenspace and vegetation to be livable. As a result, the oft cited utility message of allowing greenspace elements to die during drought can actually exacerbate the effects of drought and have unintended collateral impacts.
This is particularly important when it comes to vegetation that can take years to mature like trees. While grass and some shrubs can be replaced relatively easily, trees can take decades to attain their full mitigating effects on the urban climate. Trees in irrigated landscapes also become dependent on regular watering. When watering is reduced—and especially when it’s stopped completely—these trees will die.5 The challenge for water suppliers is to support the survival of trees through judicious use of scarce water resources, while minimizing or eliminating wasteful water use.
ARE YOU THIRSTY?
The volume of water required by vegetation is a function of environmental factors (temperature, relative humidity, precipitation), biological factors (evapotranspiration rates) and physical factors (soil type, gradient). Using these factors proactively can significantly reduce the water used by irrigation—without detriment to the plant.
In fact, we tend to overwater our landscaping. Even when customers switch from turf to xeriscape, applying a “rules-of-thumb” approach to urban irrigation usually prevents the realization of potential water savings:
[K]nowledge of actual plant usage of irrigation water in urban landscapes is unfortunately lacking, so residential outdoor water use is largely controlled by homeowners’ perceptions and by recommendations from local municipalities. These are both typically guided by historical practices that favor liberal water use to avoid plant mortality, rather than a scientific understanding of water requirements. Consequently, even potential water savings from replacing a mesic [moisture intensive] yard with xeric [dry] landscaping are often unrealized.6
An analysis of actual biological water requirements against recommendations from municipal agencies in the Phoenix, Arizona area indicates that this rule-of-thumb philosophy results in watering rates that are between four and 18 times that actually required by the vegetation. Reducing that demand could easily save the United States billions of gallons of water each day.
SERVING THE CUSTOMER, SAVING WATER
With so much of our water potentially being wasted, utilities need systems that can educate their customers on correct watering requirements and to give them the tools to manage that use. By combining usage data—particularly highly granular data associated with Advanced Metering Infrastructure (AMI)—with geospatial, remote sensing data, geological and meteorological data, an assessment of landscape coverage and watering needs can be calculated to create individual irrigation schedules.
This type of individualized assessment, tailored for current, real-time conditions, is just the type of information our customers need and want from service providers. As noted by Thomas Volo:
[H]omeowners and landscape managers must understand the specific needs of their particular landscaping. A “one-size-fits-all” approach or following the coarse distinctions made in municipal recommendations will likely result in more water applied than is necessary to achieve desired benefits.6
FATHOM provides the basis for these type of customer-centric services. Through FATHOM Meter Data Management (MDM) and FATHOM U2You Customer Portal, the information necessary to understand individualized consumption and the means to communicate change are available to both the utility and the customer to assist in making cogent decisions on water use. Combined with the FATHOM Store, utilities have a channel to adopt complementary technologies and services that provide increasing value to their customers.
As highlighted by Amir AghaKouchak in the journal Nature, “demand management, conservation, public outreach, technological innovation for water conservation and more-flexible market-based solutions and infrastructure adaptation are fundamental to responding to increased demands and climate-change stress in the future.”7
FATHOM is that solution.
1http://www.epa.gov/watersense/pubs/outdoor.html, accessed 1 Sep 15
2NASA/Goddard Space Flight Center. “Vegetation essential for limiting city warming effects.” ScienceDaily. ScienceDaily, 25 August 2015. <www.sciencedaily.com/releases/2015/08/150825205914.htm>.
3http://www.nasa.gov/mission_pages/terra/news/heat-islands.html, accessed 1 Sep 15
4Lahouari Bounoua et al, Impact of urbanization on US surface climate, 2015 Environ. Res. Lett. 10 084010 (http://dx.doi.org/10.1088/1748-9326/10/8/084010)
6Thomas J. Volo, Enrique R. Vivonia, Benjamin L. Ruddell, An ecohydrological approach to conserving urban water through optimized landscape irrigation schedules, Landscape and Urban Planning, Volume 133, January 2015, Pages 127–132
7Amir AghaKouchak, David Feldman, Martin Hoerling, Travis Huxman, Jay Lund, Recognize anthropogenic drought, Nature Vol 524:409, 27 August 2015