Green roofs, green walls, green parking lots, shade trees, the greening of urban spaces in general, the restoration of urban waterways, wetlands and the re-greening of brownfield areas; can all be thought of as different techniques to nurture a green living skin (or at least a greener skin) over regions of urban development. While there are many important differences between each of these separate techniques as well as their underlying technologies they all share a common overarching goal of bringing an analog of the natural living green skin that characterizes the natural landscape back into our urban areas. They all promote the restoration and re-integration of these heavily populated areas back into the surrounding natural environment.
Promoting the use of green re-surfacing (such as green roofs or the planting of shade trees for example), fostering the expansion of urban green spaces and restoring often neglected and polluted waterways and wetlands to their natural state yields large benefits for water quality, lowered energy and potable water use. It also improves the livability of our cities and reduces their environmental footprint helping to mitigate large global problems such as climate change and water scarcity. Furthermore by reducing the environmental problems associated with the urban environment the green living skin can save lives, improve city dwellers health and save enormous amounts of money that would otherwise be spent on the chronic health problems caused by smog.
Besides the measurable and important benefits of lowered energy consumption, lowered peak energy consumption, reduced storm runoff, increased water quality, reduction in urban smog etc. there are many hard to quantify benefits for human well-being that derive from the aesthetic and psychological impact of a greener environment on a city’s population.
There is also an important health impact; heat waves are dramatic killers and as the global temperatures rise, these heat waves will become longer and more severe. Heat waves not only cause dramatically higher peak energy usage – taxing electric systems to their limits – they can lead to large spikes in serious health problems for vulnerable people in affected areas and have been responsible for thousands of heat related deaths.
Cities that have a Living Skin Are Better Suited to Survive Global Warming
Greener cities will be more adapted to survive the hotter extremes that climate change is guaranteeing they will experience. And furthermore greener cities that are protected by a green living skin will contribute far less to global warming than barren concrete jungles do, both because the green living skin is also a carbon sink and because by saving energy overall and by saving even larger amounts of peak demand energy they will produce much less CO2 than cities that do not embrace this ethic.
Killer heat waves, such as the killer heat wave that struck much of Europe in 2003 and that caused an estimated 70,000 heat-related deaths are going to become increasingly common throughout the world as the long term effects of global warming become ever more pronounced. Cities that protect themselves with a green living skin will fare much better in these extreme weather events than those that do not.
The Urban Heat Island is an Energy Hog
As urban areas have spread out to cover vast regions they have begun to create their own weather. The vast expanses of concrete and asphalt have lead to what is known as the urban heat island effect. Big urban areas average around 3°F warmer than surrounding vegetated rural areas; this effect can rise to higher levels during summer heat waves
A Lawrence Berkeley National Laboratory study for the DOE (Department of Energy) “Energy Saving Potentials and Air Quality Benefits of Urban Heat Island Mitigation” has found that in the United States this increase in air temperature is responsible for 5–10% of urban peak electric demand for a/c use, and as much as 20% of population-weighted smog concentrations in urban areas.
The study ran a computer simulation for the L.A. basin and found that “resurfacing about two-third of the pavements and rooftops with reflective surfaces and planting three trees per house can cool down LA by an average of 2–3K (degrees Kelvin equivalent to 3.6-5.4 °F). This reduction in air temperature will reduce urban smog exposure in the LA basin by roughly the same amount as removing the basin entire on-road vehicle exhaust [my emphasis]. Heat island mitigation is an effective air pollution control strategy, more than paying for itself in cooling energy cost savings.”
This study focused on reflective re-surfacing that has the goal of increasing the albedo or reflectivity of a surface so that more heat is reflected back up into the air and less heat is absorbed. This is complimentary to green living skin re-surfacing and is applicable in areas where it is not feasible to apply a green living surface. For example on road surfaces, high use parking surfaces, or on roofs with a steep incline for example.
For an in depth look at green parking lots see our three part article series on the area of green parking lot design: Green Parking Lots: Part I – The Many Problems with Paving
Protecting our Cities with a Living Green Skin Could Reduce Health Care Costs and Save Lives
The dramatic reduction in urban smog that can be achieved by reducing the urban mean and peak temperatures will make cities much more livable and improve the long term health of city dwellers. Smog related health problems such as asthma, emphysema and chronic bronchitis can become sever in cities such as the L.A. basin and are an increasing problem almost everywhere. These smog related health issues are also very expensive.
The South Coast Air Quality Management District has this to say about the Los Angeles basin or South Coast Region, “A 1989 study funded by AQMD and conducted by Dr. Jane Hall of Cal State Fullerton found that meeting federal clean air standards for ozone and fine particulates in the South Coast region would provide $9.4 billion in health-related benefits each year. The study found that 98% of the four-county basin’s population of 13 million is exposed to unhealthful air, with children especially vulnerable. In addition, 1,600 people die prematurely as a result of exposure to air pollution, according to the study.”
That is an annual saving of almost $10 billion for just a single metro region! Re-surfacing and growing a living skin over the urban areas of the South Coast could be financed from the associated health care saving alone.
In addition to smog related health care problems the overall improvement in urban water quality and especially the significant reduction in the incidences of sewage overflow events will also lead to a better health environment and a reduction in associated health costs. Water pollution is a serious health issue in urban areas and polluted runoff creates a persistent health hazard and degrades the quality of water resources in the ground and in the surface waterways, wetlands and beaches.
How Green Roofs and Green Walls save Energy and Save Money
Promoting the greening of our urban landscape is not only aesthetically pleasing it yields significant economic benefits that directly impact the bottom line and can lower the on-going operating costs for buildings and other urban installations such as parking spaces. For example green roofs and green walls can lower the heating and cooling bills for buildings that incorporate them. During hot summer days a green roof (or sun-facing green wall) forms a buffer zone between the building and the blistering summer sun. By shading the underlying roof (or sun-facing wall), it prevents the building’s structural surfaces from heating up and increasing both the outdoor and indoor air temperatures.
Conversely during cold outdoor conditions prevailing during winter months and during the night hours of Spring and Fall the vegetative living matrix comprised of the bio-mass of the root systems and plant cover that is provided by the green roof or green wall provides an extra layer of insulation outside the structural skin of the building thereby reducing heat loss. The thermal mass of the green skin (roof or wall) also smoothes out the swings between daily minimum and maximum temperatures and this also contributes to over all improvements in the buildings thermal performance. During hard winter conditions when the biomass of a green roof freezes over its insulation value drops.
It is important to state that each single building site will present its own characteristic profile and that therefore energy savings will vary from site to site. But the savings can be very dramatic as was documented in a study by National Research Council of Canada, “Thermal Performance of Green Roofs through Field Evaluation.” This study has shown that green roofs can be very effective at reducing the heat transfer through a roof, thus saving energy. A reduced average daily energy demand of 75 percent test was documented in a test facility with a 400-square-foot green roof. Green roofs accomplish this dramatic reduction in the heat flow into the structures they protect through a combination of shading, insulation, evapotranspiration and thermal mass.
For an in depth analysis of sustainable building design and techniques see our four part article series on the subject: The Green (or Sustainable) Building: Part I – What Is the Green Building DNA?
Can we tame the Concrete Jungle with Urban Forests and Green Roofs?
Our world’s sprawling urban landscapes have been denuded stripped of their natural protective cover and turned into harsh unnatural environments that are susceptible to extreme temperatures and that gobble staggering amounts of energy and water to sustain themselves. The world’s urban areas – and especially the rich industrialized world’s urban areas – contribute a disproportionate share of the world’s global warming gases though their massive energy consumption. They also suck up massive quantities of potable water and because much of their surfaces are hard paved over contribute to polluted storm surge runoff, which taxes and increasingly overloads the surrounding water systems.
We have created these vast cement jungles with very few living surfaces left in their midst. Increasingly we are becoming aware that there is a growing cost associated with this type of urbanity; a cost that is becoming increasingly unsustainable.
Perhaps the time is ripe for a profound rethink and reset in our ideas and philosophic notions of the urban built over space, of our cities and towns; of what these population dense areas should be like and how they should be designed and retro-fitted.
One study estimated that each tree planted in an urban area saves $200 in energy savings alone. That same single tree also makes the spot it graces slightly more livable in many other ways; by providing shade, supporting wildlife, filtering the surrounding air, providing quiet (in fact trees absorb and diffuse sound), helping to mitigate strong winds and so forth. Just imagine what an entire urban forest can do. Just the simple act of planting trees along roadways and other available surfaces can help improve a cities thermal profile and create a much more livable environment in other ways.
Skeptics – who like to define themselves as realists – will speak about the costs of retro-fitting a city with a green living skin and may dismiss the whole idea of a new green urbanity as some kind of New Age fuzzy headed mysticism.
But it is precisely on hard measurable, quantifiable cost metrics that a green urban philosophy can be justified. The cost savings realized by reduced energy expenditures; the huge savings of both lives and annual reduced health costs that arise from the chronic (and very costly) health conditions associated with urban smog; the savings in the needed sewage treatment facilities and water usage. All of these are quantifiable and compelling arguments for adopting a green urban design philosophy.
The aesthetic improvements of the urban space, the fostering of urban habitat and an increased livability for all are icing on the cake. The justifications for taming the concrete jungle and greening our cities rests on solid ground and is becoming increasingly vital to the continued vitality of our cities and urban areas in a world of increasing temperatures and ever higher energy costs.
© 2009, Chris de Morsella. All rights reserved. Do not republish.