We all remember the Ala Wai Canal sewage spill of 2006. It°s become quite the urban legend: 40 days of rain, insurmountable storm water runoff, raw sewage overflow, flesh eating bacteria, RIP fallen hero.
Photo: Linda S. Valaquez, Greenroofs.com
Since then, the City and County of Honolulu has taken to overhauling Honolulu's sewer systems. Still, every time the rainy season comes around, I gag in anticipation of a possible recurrence. It turns out there is a proven solution to our fecal faux pas, one that is great for the environment and pleasing to the eye. Enter German engineering, par excellence: The Green Roof.
Also known as living roofs, green roofs use vegetation in place of traditional roof cover like shingles or tiles. Although they have technically been around since humans emerged from their caves and started building their own dwellings, it wasn't until the late '70s that German landscapers formally organized to research the technology and its potential applications, ultimately proposing living green roofs as a way to ameliorate the urban environment. Since then, the study and implementation of green roofs has revealed their wide-ranging utility and positive environmental impacts.
Beyond their obvious aesthetic advantages, green roofs have been shown to increase the energy efficiency of the buildings beneath them, as the vegetation and soil act as insulation against the extreme heat of the traditional lifeless rooftop. They provide habitat for urban animals and insect species, increase green space, allow for urban food production and improve air quality.
According to Leyla Cabugos, a local champion of green roofs and a graduate of UH Manoa's Department of Botany, the benefits of green roofs in Hawai'i are amplified particularly because of our long growing season, year-round sunshine, frequent rains and outdoor lifestyle. Beyond that, Cabugos notes, "If the proper medium is chosen, I would also emphasize the ability of green roofs to filter and reduce the amount of storm water off roofs."
This is where it's pertinent to visit the murky depths of the Ala Wai Canal once again. Not only do green roofs keep low-rise buildings cooler and add a missing botanical contingent to urban areas, but also their greatest ecological function is in their storm water management capacity. Imagine between 15 to 90 percent of rainwater runoff being absorbed into ubiquitous green roofs, depending on rain intensity and green roof soil depths. Plants intercept and delay the runoff alleviating combined sewer overflows. Eventually the water will return to the surrounding atmosphere by evaporation and transpiration. Green roofs not only absorb storm water, they filter it as well, returning cleaner water to the existing watersheds and surrounding ecosystems. This means fewer brown water advisories for surfers and swimmers, a cleaner shoreline and a healthier marine environment.
In 2006, the year of the Ala Wai sewage spill disaster, Hawai'i's legislature commissioned a study on the feasibility of green roofs in Hawai'i. They found that in the areas of Waikiki, Kaka'ako and Downtown, there are over 10 million square feet of rooftop perfect for greening. Once the legislature was briefed on the value of green roofs, they conducted a survey of residents and found that 77 percent of the residents surveyed were in favor of seeing these rooftops greened.
So what in the world is the hold up? "Industry needs to push for green roofs in the same way they have for PV and wind energy," says Jacce Mikulanec, former policy advisor to City Councilman Donovan Dela Cruz. Cruz worked with Councilmember Ann Kobayashi to produce a legislative package focused on the environment and energy that allowed a density bonus for structures that included green roofs. "The Committee never voted on the measure, despite support from the environmental and architectural communities. It expired a year later."
Indeed, without government subsidization in the forms of grants, tax incentives, density bonus allowances or low interest loans (to name a few), it seems that the greening of Hawai'i's roofs might be yet another Earth-lover's pipe dream. Green roofs are expensive and without the legislative mechanisms in place to offset the initial increased expense, developers and private property owners are unlikely to put up the money. The public funding of green roof projects also requires the State to spend money, something it doesn't really have much of at the moment.
According to Linda Cox, professor in the Department of Natural Resources and Environmental Management at UH Manoa, who worked on the state commissioned study, the hold up boils down to a need for more research. "No technology is readily available for tropical green roof systems, so we are furiously writing grants to set up demo sites and collect data. Long term investment is needed and at this time that is tough."
Leyla Cabugos echoes Cox's sentiments, noting the need for the development of green roofs composed of locally derived materials. This would not only reduce the cost, but also make the practice more sustainable.
But all hope is not lost. Green roofs are popping up everywhere across Europe and the United States, where cities are offering a variety of models for the large scale adoption of the technology and demonstrating its cost effectiveness. In the U.S. alone, Chicago, Minneapolis, Portland and New York have used various policy mechanisms to successfully and significantly increase the square footage of green rooftops. In Hawai'i, community interest in green roof technology can drive its development and expansion, despite the lack of governmental support. The 2006 feasibility study, for example, concluded that the lack of public awareness and understanding of the technology was one of the major barriers to change.
Next time someone harkens back to those dirty days of 2006, share with them the utility of green roofs. They'll not only green our skyline, they'll make our oceans a brighter shade of blue.