European airport greenroofs a potential model for north america

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"EUROPEAN AIRPORT GREENROOFS - A POTENTIAL MODEL FOR NORTH AMERICA"
By Linda S. Velazquez, ASLA Associate, LEED AP
Greenroofs.com Publisher & Design Consultant
with contributions by Benjamin Taube, City of Atlanta Environmental Manager

Abstract:

Airports occupy and consume huge areas of land mass, destroying ecosystems and creating massive urban heat islands of impermeable, hot surfaces. For example, the area of roofs and pavement at the Atlanta Hartsfield-Jackson International Airport (ATL) is estimated at over 70,500,000 square feet, or 1,619 acres! When compared to surrounding undeveloped areas, ATL infrared imagery, provided by NASA, clearly shows up to over 55°F thermal variations between the terminal, concourses, runways, parking decks and lots, cargo and other airport support buildings. The resulting loss of natural greenspace greatly impacts stormwater management, loss of habitat and biodiversity, creates noise, air and water pollution, and on a large scale, contributes to global warming.
In addition, we know how the numerous ecological advantages of extensive greenroofs could help mitigate each and every one of these environmental problems. Yet airports, as a unique development type, also offer their own particular set of construction design prerequisites and issues that are not applicable to a typical urban environment – in particular, security and safety concerns.
Specifically, stormwater infrastructure engineering must immediately provide fast and efficient drainage to all paved surfaces. And the recreated natural areas of runways and surrounding fields are designed to avoid attraction of birds, which many times get drawn into jet engines creating a potentially hazardous and life threatening situation.
Even given greenroofs’ ability to reduce stormwater infrastructure concerns, to date airport authorities outside of Europe have been hesitant to consider vegetated roofs mainly for fear of attracting birds. However, many airports in Europe have successfully constructed greenroofs atop parking garages, hangers, and even terminal buildings, without increasing their yearly number of “bird strikes.” Bird and wildlife hazard statistics and accompanying industry support will be identified. This paper will attempt to examine the impacts of using a greenroof within airports as well as address some of the potential barriers to greenroofs, in particular the real danger of attracting birds.

To make the case for the implementation of airport greenroofs worldwide, greenroofed buildings will be reviewed at the following international airports, offering insight as to local motivating factors or market drivers; the resulting ecological, aesthetic and economic benefits; and their specific design considerations including appropriate system and plant types, and other elements necessary for a safe yet green environment:
• Schiphol International Airport, Amsterdam, the Netherlands (AMS);

• Frankfurt International Airport, Frankfurt, Germany (FRA);

• Kloten International Airport, Zürich, Switzerland (ZRH)
Bird and wildlife management techniques and design considerations will be discussed, along with “Lessons Learned” from our successful European airport greenroof counterparts. Finally, using the Atlanta Hartsfield-Jackson International Airport - “the World’s Busiest Airport” – as an example, we will present a design scenario of how Atlanta’s largest urban heat island could be significantly mitigated by incorporating greenroofs. We aim to help further airport greenroof interest by encouraging continued research into these international examples of sustainable design and development.

Air transportation is an international growth industry and forecasts indicate that air traffic volumes will continue to grow, even after the massive decline in 2001 following the 9/11 terrorist attacks, and “Thousands of airports will need to be expanded, or built, to handle the Federal Aviation Administration's projected 45% increase in flights by 2020.” According to the U.S. Environmental Protection Agency and the General Accounting Office, this tremendous growth will undoubtedly contribute to the existing pollution as medical studies reveal pollutants from jets can cause heart failure or respiratory disease. On a large scale, sealed airport surfaces contribute to global warming and cause crop damage, acid rain and reduced visibility^¹.

Airports across the world occupy and consume huge areas of land mass, destroying ecosystems and creating massive urban heat islands of impermeable, hot surfaces with their immense amount of concrete and asphalt. By incorporating greenroofs within these vast airport facilities, it is extremely probable to offset the temperature increases caused by the amount of impervious surface.
The Current Situation at ATL
Atlanta has the dubious distinction of claiming our airport as “The World’s Busiest Airport.” Aviation General Manager Benjamin R. De Costa states that as the Metro Atlanta and the southeast continue to grow both in terms of population and economic development, so does Atlanta Hartsfield-Jackson International Airport (ATL). Like many high traffic airports worldwide planning for future traffic demands, ATL must modernize and expand its current airport. The City of Atlanta and the airlines at Hartsfield-Jackson have authorized the Airport to spend an impressive $5.4 billion towards a 10-year development program. Currently, the ATL passenger terminal complex measures 130 acres (52.6 hectares), or 5.7 million square feet^². Take into consideration that the total area of roofs and pavement at ATL is estimated at over 70,500,000 square feet (65,496,643 m2), or 1,619 acres^³.
NASA has been conducting a land use analysis study of Atlanta through its Project ATLANTA (ATlanta Land use ANalysis: Temperature and Air quality) since 1996. Studies show that the temperature in downtown Atlanta is often 10° F warmer than the surrounding outlying areas and the added heat also contributes to Atlanta’s air quality problem as the 10-degree rise in temperature doubles the amount of ozone that is produced^⁴. According to NASA Senior Research Scientist Dr. Dale A. Quattrochi, Atlanta's urban heat island is also creating its own weather^⁵. Situated just 10 miles south of downtown Atlanta, the massive amount of impervious cover at Atlanta Hartsfield-Jackson International Airport adds to the huge heat island and contributes to the area’s rising temperatures.


May 1997 color satellite photo of the greater Atlanta area. The Chattahoochee River and green areas are clearly noticeable among the developed areas.	Thermal infrared photo of the greater Atlanta area including the airport, seen in red, on the lower right side.

The study has also measured and modeled the rapid growth of the Atlanta, Georgia metropolitan areas since the early 1970’s and analyzed the impact on the region’s climate and air quality. The NASA chart below shows the effects of urbanization and how land use affects the magnitude of the heat.

When compared to surrounding undeveloped areas, the ATL infrared imagery shown below clearly shows up to over 55°F of thermal variation between the terminal, concourses, runways, parking decks and lots, cargo and other airport support buildings. The absence of natural greenspace here greatly impacts stormwater management, loss of habitat and biodiversity, creates noise, air and water pollution, and on a large scale, contributes to global warming.

May 1997 infrared imagery of ATL terminal, concourses, runways, parking and cargo areas. Notice how the highest temperatures, shown in red, are the roof surfaces.

NASA research recommends planting or preserving more trees and greenspace and using light-colored building materials that reflect solar energy to improve Atlanta's air^⁶. And we know how the numerous ecological advantages of extensive greenroofs could help mitigate other environmental problems such as reducing noise volumes and providing habitat for small animals.

Yet airports, as a unique development type, also offer their own particular set of construction design prerequisites and issues that are not applicable to a typical urban environment – in particular, security and safety concerns. One issue is the stormwater infrastructure engineering which must immediately provide fast and efficient drainage to all paved surfaces.

Atlanta airport stormwater facts indicate that two main drainage basins handle most of the detention/drainage within the airport infrastructure and prior to the 5th runway; the stormwater detention on the SE side of the airport is supported by about 75% of all runoff from the airport. South of the 5th runway a large detention structure is being installed and under the concourses, ramps, and south cargo are holding systems to catch the first flush for pollutant removal^⁷. According to a recent edition of Grading and Excavating magazine, the newer airport facility features four separate glycol retention/detention systems, each using 180 ft. of 48-in.- and 15-in.-diameter pipe buried 25 ft. deep. The pipe serves as a containment system for stormwater and deicing-solution runoff from the deicing pads. Beneath each deicing area is a retention/detention system to capture deicing fluid and/or stormwater runoff. Hartsfield's system is four 100- x 100-ft. holes containing three rows of Advanced Drainage System (ADS) polyethylene (PE) pipe buried 22-25 ft. deep. The pipe serves as a fluid-holding pen, slowing dispersal to the allowable outflow rate^⁸.

This airport example is representative of aviation facilities worldwide and identifies some of the developmental impacts on the land, illustrating the complex, strategic engineering necessary for the quick and safe removal of airport stormwater volumes. Thousands of lives are at stake daily on these impermeable airport surfaces of runways, taxiways, and shoulder areas. Yet impermeable airport roof surfaces also cover a large percentage of total paved surfaces and greenroofs offer an attractive opportunity to help alleviate the two greatest environmental concerns of stormwater and heat islands while possibly providing other ecological advantages.

Wildlife and Airport Specific Design Considerations
An airport environment creates its own flight safety design challenges, necessitating specialized spatial planning measures to consider both aviation and nature. Most public-use airports have large tracts of open, unimproved land that are desirable for added margins of safety and noise mitigation, but they often attract hazardous wildlife. The recreated natural areas of runways and surrounding fields are designed to avoid attraction of birds, which many times get drawn into jet engines creating a potentially hazardous and life threatening situation. Correct siting separation criteria of aircraft movement areas, approach or departure airspace regulations, and controlling land uses are measures used to discourage wildlife from interfering at airports.
Recognizing existing wildlife attractants, as well as mitigating the creation of new wildlife attractants on or near the airport will help to reduce the risk of wildlife strikes, says the Federal Aviation Administration (FAA)^⁹. The wildlife species and the size of the populations attracted to the airport environment are highly variable and may depend on several factors, including land-use practices on or near the airport. It is important to identify those land use practices in the airport area that attract hazardous wildlife as large flocks near or above airfields are not simply acceptable.
Bird Management Measures
Birds use airfields as a biotope for habitat, nesting and finding food and different species will dictate different habitat preferences. In the medium and in the long term bird strikes on airfields may only be minimized by identifying the ecological conditions that attract birds to an airfield and then using habitat deterrence methods to make the airfield less attractive for species relevant to flight safety^¹⁰.
For example, U.S. Biologist Patrick Smith says grasses cut too low will attract flocks of birds or geese. Grasses that grow too high will bring rodents, which in turn attract raptors^¹¹. Birds prevail as do other living creatures by surviving through adaptation and specialization, and eventually learn to live among humans and our built environments. For additional information on habitat modification or other procedures for controlling hazardous wildlife at airports, see FAA's Wildlife Hazardous Management at Airports^¹² and the Transport Canada Control Procedures Manual Habitat Modification^¹³.
Common Methods of Chasing Birds Away
This management can be as diverse as habitat manipulation to the use of predators to repelling wildlife to lethal control of wildlife. Gunshots, blaring horns, crackers fired off with gas canisters, hand-held laser devices, noisemakers, natural predators such as sheepdogs, border collies and even falcons have all been employed in addition to bird warning systems like the “Bird Avoidance Model (BAM), the U.S. Air Force's primary bird strike risk assessment tool. BAM is an historical archive of bird information, taking data from more than 10,000 locations over the past 30 years, for over 50 different bird species^¹⁴.
Even given greenroofs’ ability to reduce stormwater infrastructure and other concerns, to date airport authorities outside of Europe have been hesitant to consider vegetated roofs mainly for fear of attracting birds. However, many airports in Europe have successfully constructed greenroofs atop parking garages, hangers, and even terminal buildings, without increasing their yearly number of “bird strikes.” So why shouldn’t we consider incorporating greenroofs on airport area structures?
Some Bird Strike Statistics:

Over 195 people have been killed world-wide as a result of bird strikes since 1988.
Every year, over 1 billion dollars is wasted and lives are endangered worldwide when birds and other wildlife collide with aircraft.
Wildlife strikes cost U.S. civil aviation over $500 million/year, 1990-2003^¹⁵.
Birds make up 97% of the reported strikes, mammals about 3% and reptiles less than 1%^¹⁶.
Over 4,300 bird strikes were reported by the U.S. Air Force in 2003.
Over 5,900 bird strikes were reported for U.S. civil aircraft in 2003.
An estimated 80% of bird strikes to U.S. civil aircraft go unreported^¹⁷.
In Germany, an average of 1,500 bird strikes is reported annually for civil and military aircraft^¹⁸.
Waterfowl (32%), gulls (28%), and raptors (17%) represented 77% of the reported bird strikes causing damage to U.S. civil aircraft, 1990-2003.
A 12-lb Canada goose struck by a 150-mph aircraft at lift-off generates the force of a 1,000-lb weight dropped from a height of 10 feet.
At least 15,000 gulls were counted nesting on roofs in U.S. cities on the Great Lakes during a survey in 1994.
About 90% of all bird strikes in the U.S. are by species federally protected under the Migratory Bird Treaty Act^¹⁹.

Bird strikes are a rather common event, but they rarely do much damage to an airplane, and most strikes happen without anyone on board knowing about it. The most infamous encounter happened in 1960 when an Eastern Airlines jet struck a flock of starlings and crashed into Boston Harbor, killing 62 people^²⁰.

Bird Strike Industry Support
A large international industry support exists to facilitate the exchange of information, promote the collection and analysis of accurate wildlife strike data, the development of new technologies for reducing wildlife hazards, and professionalism in wildlife management programs on airports. For example, Bird Strike Committee USA is a volunteer organization directed by a 9- to 12-person steering committee consisting of 2-3 members each from the Federal Aviation Administration (FAA), U.S. Department of Agriculture (USDA), Department of Defense, and aviation industry^²¹. Richard Dolbeer is the USDA/Wildlife Services National Coordinator, Airport Safety and Assistance and his office manages the national database that records wildlife strikes with aircraft each year and finds ways to keep the nation's air traffic safe from wildlife. The FAA has an Airport Wildlife Hazard Mitigation website^²². The German Bird Strike Committee (DAVVL e.V.) is very comprehensive and publishes the scientific journal Bird and Aviation (ISSN 0721-4521), a technical periodical appearing usually twice annually since 1981, offering a wealth of information on the subject in German and English^²³. And yearly regional and international conferences meet to discuss trends.
Given all the concerns of flight safety and the bird population, conservation biologists still estimate that by 2100 about 10% of all bird species probably will be extinct, killed off by habitat loss, hunting and climate change^²⁴. With all this daunting information isn’t it still possible to design airport buildings and areas with both human and wildlife safety and preservation in mind? The answer is yes, of course.
European Airport Greenroofs
The notion of airport greenroofs may be new to many of us here in North America, but when I started asking the Germans in particular about airport greenroofs, I was told that there are thousands of square meters of greenroofs on airport buildings. Within Germany alone are various greenroofs at Stuttgart, the new airport in Münich, in Bremen and the airport in Düsseldorf. France has greenroofs at Charles de Gaulle in Paris, Paris’ Orly International Airport and Bordeaux Airport. I have also seen an airport terminal greenroof in Milan, Italy and more probably exist.
After security issues, noise abatement, air quality, and preservation of greenspace are the top environmental concerns of area residents and airport management. Many greenroofing companies have established themselves in Europe offering many system types and materials, and manufacturers and providers. The following airport greenroof studies are based on European aviation authorities and company representatives responding to our information request, and are not intended to be exhaustive in scope.
Schiphol International Airport, Amsterdam, the Netherlands (AMS)
In 2002, the Schiphol International Airport management began defining their sustainable development policy and six themes were identified. Of particular interest are “Safety” and "Nature and Landscaping at Amsterdam Airport Schiphol" where they are planning to create more awareness in the next few years for the flora and fauna located on the airport grounds as well as for nature and landscaping activities. Schiphol ownership strives to ensure that the airport landscape blends into the natural surroundings in the best way possible. For example, they designed a system of canals and dense hedging to enclose the area around the new runway. The policy prerequisite to avoid bird strikes includes deterring birds from coming to the airport grounds by growing a longer species of grass and employing a team of specially trained dogs to chase the birds away. Approximate number of bird strikes at AMS in 2003: 122 (KLM figures not complete); 2002: 188; 2001: 122; 2000: 233; 1999: 200^²⁵.
The majority of roofs greened at Schiphol International Airport buildings have used Xero Flor and ZinCo products. From our research and respondents we have estimated the total airport area greenroofed at Schiphol International Airport and its surrounding Schipholrijk neighborhood to be approximately 73,730 m2 or 793,623 square feet (sf). The Schiphol airport itself contains three buildings with extensive greenroofs of 8500 m2 (91,493 sf), 3500 m2 (37,674 sf), and1330 m2 (14,316 sf). Schiphol also has two intensive greenroofs totalling 400 m2 (4,306 sf) bringing the airport total to 13,730 m2 or 147,789 sf. The Schipholrijk neighbourhood has six buildings with intensive greenroofs measuring approximately 10,000 m2 (107,639 sf) each for a total of 60,000 m2 or 645,835 sf^²⁶.

Schiphol Plaza extensive greenroof - Constructed in 1994, the Schiphol Plaza Xero Flor greenroof is situated over the main terminal and measures approximately 8,500 m2 (91,493 sf), serving as a parking garage and train railway station. Designed by Benthem Crouwel NACO, Mostert De Winter, Dutch licensees of the firm Strodhoff & Behrens Begruennungs GmbH of Gross Ippener, Germany, installed the largest extensive greenroof at Schiphol using the Xero Flor moss-sedum combination pre-vegetated mats Type XF 300c. The sedums and drought resistant mosses are set in a mineral-based Xero Terr® substrate formula with a system maximum saturated weight of 35 kg/m2 (7.168 lbs/sf); the substrate depth is just 40 mm (1.57”)^²⁷.


Schiphol Plaza; System: Xero Flor; Source: Mostert De Winter website^²⁸.	Varying colors at Schiphol Plaza; Photo: Haven Kiers^²⁹.

Schiphol Real Estate and Sky-Master extensive greenroofs - Aart Veerman, President of the International Green Roof Association and Commercial Director of Van der Tol b.v., estimated the total area on the grounds of Schiphol-Airport greenroofed by Xeroflor with sedum mats to include three roofs at 13,330 m2, to equal 143,483 sf. The other two large extensive roofs are situated on the head office of "Schiphol Real Estate" and the “Sky-Master” building.
Mr. Veerman’s company, Van der Tol b.v., holds the maintenance contract on both. He states that the maintenance of the sedums is really simple - the only extra measure is the filling of the open space between the sedum mats to account for normal yearly shrinkage. Regarding bird populations Aart says “So far as I can remember the facility-manager of Schiphol never spoke of a bird problem in relation to the sedum-roofs.”


Schiphol Real Estate Building; System: Xero Flor; Source: Aart Veerman

Schiphol Vertrekhal Noord intensive greenroofs - Inside the departure and arrival buildings are two small 400 m2 intensive patio roof gardens at Vertrekhal Noord that were built in 2001, but they are not easy to visit because of strict security regulations. These are ZinCo greenroofs utilizing Floradrain FD 25 green roof systems.

Schipholrijk intensive greenroofs - The roof gardens in the neighborhood of Schiphol-airport located in Schipholrijk measure approximately 10,000 m2 each. Office park area residents include Microsoft and Mitsubishi. Three of six greenroofs are made with ZinCo system solutions. Due to the intensive nature of these greenroofs, the ZinCo Elastodrain EL200 system was used for the driveways, because of the car traffic on the roof. Mixed systems were used on the remaining roofs using different trademarked drainage and filter material. For example, one roof garden not pictured here is made with the BACEL-system, a Dutch trademark based on Styrofoam drainage^³⁰.


Large intensive greenroof projects in Schipholrijk; System: ZinCo; Left: Mitsubishi Office Park; Source: Aart Veerman

Kloten International Airport, Zürich, Switzerland (ZRH)
Zurich-Kloten International Airport in Zürich (ZRH) is the largest airport in Switzerland and strives to symbolize a modern, comfortable and green airport. ZRH is home to a nature conservation area that covers an area of approximately 74 hectares and is only a few meters away from the edge of the runways. ZRH operations and management focus strongly on communication in the area of environmental protection, and publish an annual environmental report^³¹.
ZRH has two recent large greenroof projects which demanded a high level of effort, coordination, and communication from all participants because of its sensitive location and accompanying security measures. No data was found for bird strike counts at ZRH.

Dock E (Dock Midfield) extensive greenroof - One of the largest greenroof building sites in Switzerland, the new dispatch building at Kloten International Airport is Dock E, previously known as Dock Midfield, situated between take-off runways and landing strips. Sporting an extensive greenroof measuring 4,000 m2 (43,056 sf), Dock Midfield represents a perfect example how green space can be regained on roofs. Completed in November 2002 after years of detailed discussions, the planning group decided to install ZinCo greenroof systems. Admittance to the Dock Midfield project was limited to trained staff using registered vehicles, and strict regulations had to be followed to obey the demanding security measures of airport Zurich-Kloten.


ZRH recently seeded in June 2002.	Installing the 80 mm (3”) depth substrate.

Limited movement dictated careful planning, for example one issue dealt with how to bring up the substrate and gravel to the 18 – 22 m (59 – 72’) high roof surface while crossing a 14 m (46’) wide photovoltaic installation at the roof’s perimeters without any damage. In response, a ZinCo partner’s special vehicle utilized a pneumatic pump and placed the substrate materials onto the roof’s perimeters at three locations, where it was then spread on to the entire surface using flexible pipes at a depth of 80 mm (3”).


View of ZRH’s Dock E (Dock Midfield) – Up to 27 aircraft can be handled simultaneously ; Source: ZinCo	The ZinCo Green Roof System vegetation strip next to the 14 m wide photovoltaic installation. Along the perimeter between the fascia and vegetation, a safety strip of gravel is installed as fire prevention. Source: ZinCo

The roof construction illustrates the not often used variation of the inverted roof in Europe. Particular to inverted roofs is the fact that the insulation layer is situated over the waterproofing. “There are two main subjects that have to be taken into consideration when planning a well functioning Green Roof System on top of an inverted roof,” says Jürgen Ullrich of ZinCo. “First of all, the insulation material must maintain its insulating effect even during penetration by water. That means that inverted roofs require extruded insulation. Secondly, the Green Roof build-up must be designed so that vapour pressure can be built up.”

A flowering meadow-like roof at ZRH three years after installation; Copyright ZinCo

Separation and slip membrane TGV 21 covers the extruded insulation mats and serves as the base for the ZinCo recycling substrate. TGV 21 is permeable for vapour but resistant to water, necessary qualities for the installation of a ZinCo Green Roof System on inverted roofs. The vegetation consists of Sedum shoots at 20 – 25 pieces /m2 (2-3 pieces /sf) which are drought and frost resistant Sedum plants. Generally, Sedum vegetation is a low demanding type of vegetation, yet fertilizing and maintenance, especially weeding once to twice/ years, has to be done. Credits – client: Unique Flughafen Zürich AG; landscape installation: Behlke GmbH; design company: ARGE Zayetta; project designer and architecture: David Munz; site supervision and structural engineering: Urs Strickeisen; greenroof systems: System ZinCo; technical advice: Jürgen Ullrich, ZinCo AG; construction: Behlke GmbH & Co. KG^³².

Multi-story Car Park B (Parkhaus B) extensive greenroof –Completed in 2001, the 8,000 m2 (86,111 sf) multi-story Car Park B at ZRH also demanded specific logistic skills and equipment in bringing up the substrate to the high 50 m (164’) roof level, and a pneumatic pump was required to blow substrate and gravel onto the roof's surface.


Multi-story Car Park B (Parkhaus B) before greenroof installation^³³.	The extensive ZinCo Green Roof System used here is in its second vegetation season after installation.

Construction work was performed during daily airport vehicle and airplane traffic. The extensive ZinCo Green Roof System contains a combination of planted Sedum shoots and hydro-seeding in a sedum carpet. An anti erosion jute control net "JEG" was installed afterwards to protect the plants against wind uplift^³⁴.


The structured grid of sky lights is softened by the surrounding ZinCo greenroof vegetation shown three years after installation.	Multi-story Car Park B is now covered by a carpet of yellow. In the background an airplane is just taking off.

Credits for the ZRH Multi-story Car Park B - architect and design firm: Stutz & Bolt, Winterthur; construction: Behlke GmbH, Lennestadt; greenroof system: ZinCo System "Semiramis"^³⁵

Frankfurt International Airport, Frankfurt, Germany (FRA)
Germany and Europe’s largest airport, Frankfurt International (FRA) is ranked no. 7 in the world. At 20 square kilometers (4,942 acres) in size, FRA is also one of the most compact of the larger world airports^³⁶. As a result, one of Frankfurt International’s key issues is ecological land conservation as they strive for optimum land use with minimal negative environmental impacts in the densely populated Rhein-Main region.

The maneuvering areas between the taxiways equal approximately 500 hectares and this nature conservation area has become home for many plants and animals that are endangered elsewhere. Management techniques include developing part of the area into a heath because this type of vegetation is the best to minimize the bird strike danger here. The green areas are not watered and no fertilizer is applied. Rare birds such as the wheatear and whinchat are observed along numerous endangered toads and frogs with over 300 different plant species also found on these grounds. In contrast to many other international airports, FRA does not scare birds but relies on biotope management, which focuses on designing the airport grounds in such a way that birds are not attracted in the first place. The bird strike count at FRA averages 3 to 5 per 10,000 aircraft movements and is at the top in terms of international comparison, equal to the annual strikes at Schiphol International Airport. Furthermore, FRA operators harvest rainwater from roofs and other surfaces and are committed to nature conservation by running reforestation programs to make up for land consumed for airport purposes^³⁷.

FRA greenroofs - Plants are used extensively on building facades, within inside courts and on top of the terminal roofs. Planning and upkeep are usually handled by airport specialists who run their own airport greenhouse shops. .According to Uwe Harzmann of Optigrün international AG, Frankfurt International has greenroofs located on Terminal 1 and Terminal 2, on the cargo building and on Terminal B. The total approximate greenroofed area is 30,000 m2 (323,000 sf) with Optigrün’s having greened about 11,700 m2 (125,938 sf) of this total. Optigrün estimates that 2,400 m2 are intensive, and the rest are extensive greenroofs. Optigrün has used the following substrates depths for these greenroofs: Intensive: (40 – 60 cm 16 – 24”); Extensive 8 – 10 cm (3 – 4”).


Intensive FRA greenroofs by Optigrün international AG^³⁸.

The European Experience and Outlook
Not all European countries have experience with airport greenroofs and some officials are understandably cautious. Referring to airport greenroofs, Dr. John Allan, Head of the Birdstrike Avoidance Team of the Central Science Laboratory in York, England, believes smaller species should not present a problem but says “I would be very concerned about the possibility of roof nesting by gulls, which is becoming an increasing problem here as it is in the U.S.” The question appears to be whether they would be any more attractive than a bare flat roof^³⁹. British ornithologist and greenroof advocate Dusty Gedge agrees that in parts of the UK there are big problems with gulls nesting on roofs general. But as director of Livingroofs.org he believes such roofs around airports could be beneficial as they would in some way mitigate some of the less desirable environmental consequences of airports and airlines.^⁴⁰
Yet, Dr. Allan is most interested to hear about existing airport greenroofs elsewhere in Europe, of which he was not aware. He adds, “We are responsible for checking and approving planning applications at U.K. civil and military airports in relation to birdstrike issues and, although it has not happened here yet, the use of greenroofs in Europe suggests that it is a matter of time before we will need to address this issue in the UK.”^⁴¹
Greenroofs are simply one sustainable design element incorporated into an overall ecological airport land use plan. Stormwater retention rates, improved air and water quality, and area temperature reduction advantages can be expected to have the same effects whether situated on an airport greenroof or any other landscaped roof, as they are more dependent upon local climate factors than a type of application. Perhaps since the Europeans have been managing these natural airport areas with ecological conservation in mind from the start, bird and other wildlife design considerations and regulations are not separated in terms of natural areas of taxiways or recreated natural areas on a roof.
Does the European experience indicate birds on greenroofs are causing problems for air traffic by increasing incidences of bird strikes? Simply, there don’t seem to be any issues pertaining to increased bird strikes associated with airport greenroofs among any of the manufacturers and providers contacted within Europe. Not one person identified any specific maintenance problems or concerns for airport building greenroofs simply because they are located in an airport – in other words, greenroofs are part of the initial design process and designed according to the needs of that particular geographic area. Greenroof maintenance is integrated into the overall airport management plan and is either done by the airport itself or is handled through landscape contracts with industry professionals.
The respondents argued that birds use greenroofs as much as any other green space in nature, and usually only small birds settle on greenroofs. Moreover, birds also rest and settle on barren, naked roofs. Do they cause problems?
A Green Lining

Yes, they do, says Richard A. Dolbeer, PhD, USDA/Wildlife Services National Coordinator, Airport Safety and Assistance Program, as is illustrated in the photos below. “Based on my experience evaluating wildlife attractants around airports, I do not believe that properly designed "green roofs" would attract hazardous birds beyond background levels. In fact, such roofs might actually reduce the presence of large birds that are hazardous to aviation,” he says. “One chronic problem that we find around coastal airports in USA and Canada is nesting and roosting by gulls on flat roofs, especially gravel-covered roofs but sometimes even metal roofs. A survey we did in 1994 revealed 16,000 gulls nesting on rooftops in cities along the USA portion of the Great Lakes. This survey missed a lot of roof colonies so the actual numbers were much higher.” ^⁴².


Traditional flat roofs often do attract hazardous birds. Left: Ring-billed gulls with chicks	Right: Herring Gulls nest on a rubber roof. Photos: Richard Dolbeer

He said a similar question about 15 years ago regarding yard-waste compost facilities (would they attract hazardous birds if located near airports?) resulted in conducting two objective studies in which bird numbers by species were observed at yard-waste facilities and then compared to background levels of birds in undeveloped grassy areas of comparable size. They found fewer birds in the compost areas; thus, yard-waste composting was not incompatible with aviation safety^⁴³.

Richard Dolbeer continues, “Thus, it would be a good idea to have a study conducted to document the numbers and types of birds seen on green roofs so that you will have objective data. As I said at the start, I do not think green roofs should attract hazardous birds but the only way to definitively answer the question is to conduct a study. We already know that traditional flat roofs often do attract hazardous birds.”^⁴⁴
Successful Design Parameters
Therefore, success appears to be based on various site specific design parameters all directly relating to the local ecology. Bird species that may form large flocks and feed on airfield grassland are a concern. Another issue is the possible attraction of pigeons or gulls on roofs that are used by airport staff during break times when feeding of birds becomes likely. If flat gravel and barren roofs actually do attract larger birds, it can be argued that greenroofs can be designed to not attract the larger birds with correct vegetation, and actually deter these more hazardous types from nesting. Maintenance agreements need to be in place with either airport personnel or specific greenroof service companies.
Vegetation
One of Germany’s leading landscape architects and foremost expert on greenroofs is noted researcher and designer Bernd W. Krupka. Mr Krupka advises that construction techniques of green roof systems must be used against bird populations that are dangerous to aviation, i.e., bird species of a larger size than finches. “These construction techniques must provide a higher growth of the grass and herb vegetation in order to prevent bigger birds from landing on the roofs, though such areas with higher vegetation must be mowed or cut - the same as any meadow – in order to prevent shrubs or bushes from growing and to reduce the fire risk. In this regard it is essential that the airport management provides a job profile which shall also be applied to the remaining green spaces.” He adds that the subject still needs more research^⁴⁵.
Mr. Krupka contributed the following information: “Bird repelling green roofs can be realized with extensive and intensive green roof build-ups. For roofs with low load bearing capacities (of approx. 30 to 40 kg/m²) pre-cultivated vegetation mats made of mosses and herbs (approx. 20-40 mm in height) can be used with reinforcement of entangled filaments. Past experience has shown that birds are deterred by the entangled filaments because of a trap or snare effect. Higher grass and herb vegetation (approx. 150 to 200 mm in height) is less attractive for birds as habitats can be created with a substrate depth starting at approximately 150 mm.
For intensive green roofs ground-covering woody plants with low to medium height are predominantly eligible. There are a number of deciduous and coniferous trees available with no berries (e.g. Lonicera pileata, Juniperus sabina, Pinus montana). These trees can be successfully be used for larger green roof areas. However, monocultures should be avoided, as well as scattered tall trees which are very attractive for birds.
According to past observations, only a few little ground birds like larks or meadow pipits use extensive green roofs as habitats. On ground-covering woody vegetation types, only greenfinch or blackbirds have been observed in Germany as breeding birds so far. Gravelled roof areas are on the other hand in many cases resting places for larger birds: These can be kept off completely or at least temporary by medium-high vegetation.”^⁴⁶

The Future for ATL and Elsewhere

Interest in smart, energy-efficient buildings has been steadily growing, especially among those who manage large facilities such as airports because lifetime building operating costs can be hundreds of times more expensive than the original building itself. Lucie Griggs, director for Atlanta’s Cool Communities non-profit organization, says NASA's air-quality modeling research in Atlanta could lead to the creation of financial incentives for doing heat-sensitive construction, or changes in development laws, which in turn could lead to more possibilities with greenroofs^⁴⁷. The City of Atlanta is already on track with a greenroof atop Atlanta City Hall with plans for other government buildings and possible measures to increase greenroof development in the future.

From the successful European experience we can see that certainly greenroofs are viable alternatives to the average hot, barren airport rooftops, detached from and detracting from our natural environments. It is easy to understand how Atlanta’s largest urban heat island, Atlanta Hartsfield-Jackson International Airport, can be significantly mitigated by incorporating greenroofs, and can serve as a representative scenario of world airport architecture.
Conclusion: A Balancing Act
Using the Airport as a metaphor for the City, it is clear that through utilizing greenroofs as part of its urban infrastructure of runways, managed greenspaces, etc., we can mitigate many of our developmental impact ecological problems such as the heat islands, stormwater, habitat destruction and the like. In a similar vein "underground architect" Malcolm Wells' vision of a new American landscape includes placing infrastructure underground, and believes even airports could be located underground. Similarities remain in that humans may reconnect with nature and each other. In 1994 Wells told The Futurist magazine “The question of how to design an airport appropriate for the future can be answered as follows: Build huge, high, roofed-over spaces, allow for floor-to-floor heights of ten feet or more indoors, and pull a blanket of earth over the whole thing.^⁴⁸
Economic impacts of airport facilities and operations affect many sectors, both private and public. But we must also balance the needs of current airport land/building management and expansion plans in environmental impact terms.
Next Steps to a Greener Airport Rooftop Environment
Yet what may appear to be a call for an immediate action or an obvious environmental solution to the many developmental woes presented by airport construction does need to be tempered with continued review and research of airport wildlife mitigation design principles at regional airports worldwide. Our position is to encourage safe, site specific design and maintenance strategies which include the technology of organic greenroof architecture. Public policy stakeholders worldwide can benefit from further study of numerous European regional planning and zoning procedures which include various types of airport greenroofs and systems. We hope to encourage further dialogue and information sharing between international governments and bring to light that not only are airport greenroofs possible, they are currently in existence without mishap. Here then is opportunity to form an international multi-disciplinary team of airport stakeholders including greenroof design professionals, safety experts, wildlife biologists, ornithologists, researchers, and government policy makers.
We believe we need to not only embrace this concept, but further study and develop it to best fit our wide geographic and regulatory needs. Land use practices known to threaten aviation safety are not acceptable, and agree with Dr. Richard Dolbeer in that we need to have studies conducted to document the numbers and types of birds seen on existing European airport greenroofs and representative North American greenroofs across our various climate zones to accumulate objective data. The FAA will most certainly discourage the development of any questionable sites, including sustainable greenroofs, if studies show that they support or encourage potentially hazardous wildlife species. Once local problem bird populations are clearly identified the judicious selection of the correct vegetation palette should ensure a comfortable margin safety.
So, in this case, it appears necessary to err on the side of caution before we jump wholeheartedly into promoting airport greenroofs worldwide. Do we hear any student, policy or government takers willing to document the European airport greenroof experience, please?

- Linda S. Velazquez and Benjamin Taube

“Are human beings and the natural world destined to be at odds forever? Or can we, so long estranged from the world that produced us, learn to live as gently, as gracefully, and – with great good luck – as beautifully here as do all the rest of the world's creatures?” – Malcolm Wells^⁴⁹

All rights reserved, Greenroofs.com, LLC. Permission is granted to Green Roofs for Healthy Cities to include paper in the proceedings of the Third Annual Greening Rooftops for Sustainable Communities Conference, Awards and Trade Show, 2005.

Footnotes Page

1“Inventor takes airport design to new heights,” by Gary Stoller, USA TODAY 1.12.04 http://www.usatoday.com/money/companies/management/2004-01-12-starry_x.htm.

2 http://www.atlanta-airport.com/Default.asp?url=sublevels/airport_info/gmpage.htm.

3 Benjamin Taube and Georgia Tech.

4 Dr. Jeffrey Luvall, NASA, Personal Communications, 6.01.

5 Dr. Dale A. Quattrochi, Personal Communications, 6.22.01.

6 Dr. Jeffrey Luvall, NASA.

7 Atlanta Department of Aviation.

8 Grading and Excavating magazine, November/December, 2004.

9 http://www.faa.gov/arp/pdf/5200-33.pdf.

10 The natural environmental features of the airfield of Holzdorf and measures for bird-strike prevention, Bird and Aviation, Vol. 24 (2004), Vol. 1 by K. Hahn-Becker, http://www.davvl.de/Volu%20englisch/2004/Hahn.pdf.

11 November 19, 2001: “FAA Targets Bird-airplane Collisions,” Sacramento Bee, By Matthew Barrows, http://wildlife.pr.erau.edu/News.htm.

12 http://www.faa.gov/arp/pdf/manfin.pdf.

13 http://www.tc.gc.ca/civilaviation/aerodrome/menu.htm.

14 http://www.birdstrike.org/.

15 Ibid.

16 http://wildlife.pr.erau.edu/WildlifeManagement.htm.

17 http://www.birdstrike.org/.

18 German Bird Strike Committee, http://www.davvl.de/Seite53e.htm.

19 http://www.birdstrike.org/.

20 November 19, 2001 – “FAA Targets Bird-airplane Collisions,” Sacramento Bee, By Matthew Barrows, (http://wildlife.pr.erau.edu/News.htm.

21 http://www.birdstrike.org/.

22 http://wildlife.pr.erau.edu/index.html.

23 http://www.davvl.de/Seite2e.htm.

24 Dan Vergano, USA TODAY, http://www.usatoday.com/news/science/2004-12-13-bird-species_x.htm.

25 Sustainable Development at Amsterdam Airport Schiphol 2003 PDF - http://www.schiphol.nl/media/portal/_schiphol_samenleving/pdf/pdf_files/verslag_vo_2003_uk.pdf.

26 AART Veerman of the International Green Roof Association and Heidrun Eckert of ZinCo International.

27 http://www.bam.nl/baminternet/baminternet/portalen/mostertdewinter_nl/index.jsp.

28 Ibid.

29 Landscape Architect Haven Kiers.

30 AART Veerman of the International Green Roof Association and Heidrun Eckert of ZinCo International.

31 2003 Environmental Report, Zurich Airport, April 2004 - http://www.unique.ch/dokumente/?ID_site=2&sp=en&doku=Environmental%20Report_2003.pdf&dtit=Unique+2003+Environmental+Report.

32 Jürgen Ullrich, ZinCo Press Report ”Dock Midfield Under a ‘Green Hat’” PDF, October 2004, prepared for Linda S. Velazquez.

33 www.zinco.de.

34 Jürgen Ullrich, ZinCo Press Report “Dock Midfield Under a ‘Green Hat’” PDF, October 2004, prepared for Linda S. Velazquez.

35 www.zinco.de.

36 http://www.ausbau.fraport.com/cms/default/rubrik/2/2230.why_expand.htm.

37 http://www.fraport.com/cms/environment/rubrik/2/2866.nature_conservation.htm#Bird%20Strike.

38 Uwe Harzmann, Personal Communications, 11.15.04.

39 Dr. John Allan, Personal Communications, 12.04.

40 Dusty Gedge, Personal Communications, 12.03.04.

41 Dr. John Allan, Personal Communications, 12.04.

42 Dr. Richard Dolbeer, Personal Communications 12.06.04, and Dwyer, C. P., J. L. Belant, and R. A. Dolbeer. 1996. Distribution and abundance of roof-nesting gulls in the Great Lakes region of the United States. Ohio Journal of Science 96:9-12.

43 Dr. Richard Dolbeer, Personal Communications, 12.06.04, and Gabrey, S. W., J. L. Belant, R. A. Dolbeer, and G. E. Bernhardt. 1994. Bird and rodent numbers at yard-waste compost facilities in northern Ohio. Wildlife Society Bulletin 22:288-295; Gabrey, S. W. 1997, Bird and small mammal abundance at four types of waste-management facilities in northern Ohio, Landscape and Urban Planning. 37:223-233.

44 Dr. Richard Dolbeer, Personal Communications, 12.06.04.

45 Bernd W. Krupka, Personal communications, 12.02.04.

46Krupka, B.W., Bird and Aviation (ISSN 0721-4521): Flat roofs on airports - advantages by vegetation. Volume 10, Issue 1 - translated from Bernd W. Krupka by Julia Schumayer of ZinCo International, 1.12.05.

47 The Atlanta Journal-Constitution, "NASA studies how to cool area as heat builds up" by Kevin Duffy of 04/18/04, http://www.ajc.com/news/content/business/horizon/0404/19pavement.html?urcm=y.

48 http://www.life.ca/nl/40/underground.html Natural Life Magazine, # 40.

49 September/October 1994: The Futurist magazine.

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