Green Infrastructure Lets Nature Help Carry the Load of Our Cities
Ashwani Vasishth
Associate Professor, Environmental Studies Director, Sustainability Studies vasishth@ramapo.edu
(201) 684-6616 http://phobos.ramapo.edu/~vasishth
Our urban areas desperately needs investment in infrastructure. However, we have come to a place, removed from nature, where we think of infrastructure rather narrowly. We plan to build with concrete and steel and asphalt, importing electricity and water, exporting waste and pollution, and relying increasingly upon the automobile to carry us about a landscape that we have segmented out into distant and disjointed uses.
But there is another form of infrastructure that we could just as easily and far more cheaply deploy to help carry the burden we place upon the land. Green infrastructure. The goods and services nature would dearly love to offer us, ours for the taking and only in exchange for an intelligent recognition of our ecological context, and a respect that is due the land.
Dark, heat-absorbing, impervious surfaces, namely roofs, roads, and parking lots, are the quintessential hallmark of urbanization. This often unmitigated fact has a range of significant and cumulatively detrimental effects on the ecological and bio-geo-chemical processes and functions that underwrite our cities and shape our inhabited world. We reduce the effective carrying capacity of the land by generating needless waste and pollution. This waste is not merely waste, but rather an actual increase in the costs we must incur in the form of the enhanced infrastructure needed to counteract our often unthinkingly expressed preferences. We choose NOT to live lightly upon the land, and then groan at the added burden our civilization must carry.
Conventional building practices result in increased ambient temperatures due to the proliferation of heat-absorbing surfaces. Urbanized regions can be 4 to 10 degrees Fahrenheit hotter than their surrounding countryside. This generates increased biological and material heat stress, a substantial part of which we could easily alleviate, at little additional cost. This also increases the load we place on our air conditioning systems, consuming electricity that we could very easily put to more productive uses. The higher temperatures also increase the formation of photochemical smog. And groundwater recharge is reduced, even as urban stormwater runoff is increased, due to a mindless proliferation in impervious surfaces.
Our sprawling patterns of urbanization force us to drive further and longer, to and from our multiple daily tasks, increasing traffic exhaust. Our freeway surfaces
receive increased depositions of toxic dust and exhaust particles, building up through the year, nano-layer over nano-layer and quite invisible to our eyes, awaiting that first flush of the winter rains that will wash these toxins into our stormwater drains. Of course, this will require additional expenditures in water purification to maintain the quality of our water bodies.
The piece-meal and haphazard appropriation of lands for urbanization results in a needless fragmentation of natural habitats. The large-scale insertion of often non-native vegetation in the form of ornamental gardens shaped to mimic images imported from far away and long ago, the broad sweeps of synthetically maintained and copiously irrigated grass lawns, all come together to disrupt indigenous landscape ecologies and to interfere with the pulsing patterns of regional bio-geo-chemical processes. And so, without thought and without ill- intent, the land becomes more and more a receptacle for the toxic effluvia of our unconsidered urban lifestyles. All of which results, ultimately, in the more unequivocal separation of humans from nature. And in lots more of that expensive concrete and steel infrastructure stuff we need to live our lives.
With time and with technological modernization, our cities have come to rely increasingly on the bending of nature to our whim, This has lead to a corresponding reduction in our need, and so our willingness, to even think to adapt to the particulars of our environmental context. Rather than build in a vernacular, using climatically appropriate building materials and locally adapted dwelling types, we choose instead to impose our will upon the land, capitalizing on the apparent economic benefits of a mass-production mass-culture. Of course, we must then compensate for the ecological consequences of such choices through the increased use of air conditioning and heating, more of the personalized transportation infrastructure to support our lone commutes across sprawling landscapes bereft of localized neighborhood connectivity.
We choose to deny our ecological context, and impose instead our own production of place. But by denying our ecology, we come also to live more heavily upon the land. And at least some of the infrastructure we are now forced to build may have just as easily been avoided, without loss to quality of life and to our preferred lifestyles.
It doesn’t have to be this way! We can let nature back into our cities, using intelligence, innovative materials, suitable tree species and native vegetation to lighten our tread. Three strategies from urban ecology: heat island mitigations, urban forestry, and impervious surface management, together provide many of the infrastructure benefits our contemporary society needs. Together, these strategies will considerably reduce air pollution and water pollution, significantly enhance our natural water supply, substantially strengthen connectivity across the rich and diverse habitats within which we dwell, while at the same time reducing the carbon dioxide emissions that mark our copious transfer of below ground carbon into the atmosphere, in the form of fossil fuels.
• Heat Island Mitigation Measures: Lighter colored and heat reflecting building and paving materials, used for roofs, driveways and roads, would help reduce temperatures by 4 to 6 degrees Fahrenheit. This would reduce the air conditioning loads during peak demand by 20 to 25 %. This is partly due to the reduction in ambient temperatures, but also by directly cooling roof membranes by 40 to 60 degrees Fahrenheit, which substantially increases the effective life span of each of these treated roofs. (Green roof technologies have now reached a point where we have a very good understanding of how to build these and what plants to use for a low- maintenance result.) And at the same time we would also reduce the formation of smog by some 10 to 15 %.
• Urban Forestry Measures: Ecologically suitable species of trees and shrubs, strategically planted to provide shade for our built environment, would also cool the air through the entirely natural process of evaporative transpiration, even as their copious leaf surfaces help to trap toxic dust particles locally. (If they were to be planted in dense stands downwind of hot-spots such as freeway corridors with high volumes of truck traffic, residential neighborhoods in these areas would be relieved of the substantial health impacts they now face.) At the same time, and at no additional charge, they would capture and store copious amounts of rainwater, even as they penetrate the soils to increase groundwater recharge, improve the health of our quite organic soils, and provide precious habitat.
• Impervious Surface Management: There are innovative and now quite well- tested materials technologies that would allow us to make our denser landscapes more porous. The square miles of sun-baked asphalt parking lots that now frame our downtowns could easily be turned into tree-shaded, rain- water receiving reservoirs that would help recharge our water tables even as they capture and bioremediate the toxic drippings of hot commuter automobiles. (If we were to implement a 50%-tree cover strategy for our parking lots, we would substantially reduce evaporative emissions from the countless cars that now stand baking in the afternoon sun, in every downtown parking lot.) We know also how to deploy xeriscape plants that naturally need less water to grow, and so are more drought-resistant, across our lawns and gardens. We can make our cityscapes prettier even as we make them more porous, allowing nature to do many of things that it does best, and at little cost to us.
• Rain Gardens, Bioswales and Green Roofs: Particularly in cities with combined sewer-stormwater systems, but also in other cases, stormwater runoff is a wasted resource. The best and highest use of stormwater is as groundwater recharge and as catchment irrigation. Rain gardens, bioswales and green roofs allow us to attain that best use. These are landscape elements designed specifically to capture and retain stormwater for improved groundwater recharge.
By integrating such green infrastructure measures into our planning, we would come, cumulatively, to reduce our ecological footprint, and, at the same time, to increase the effective carrying capacity of our land. If we intelligently deployed more green infrastructure as an integral element of our infrastructure planning process, we would need far less concrete and steel. Ensuring that such plans are built around a green infrastructure core that takes account of ecological processes will result in substantially better returns on investment today, while ensuring a benefit stream that continues much further into the future. Green or grey, we get to choose.
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Ashwani Vasishth is an Associate Professor in Environmental Studies, and Director of the Master of Arts In Sustainability Studies program at Ramapo College of New Jersey. His research is focused on the development of an ecosystem approach to integrative regional planning, and he can be reached at vasishth@ramapo.edu, or from http://phobos.ramapo.edu/~vasishth.