Green Roofs in Urban Areas: Comparison
View Latest Version
Please note this is a comparison between Version 2 by Jessie Wu and Version 3 by Zuzana Koscikova.

The presence of green roofs in urban areas provides various ecosystem services that help mitigate climate change. They play an essential role in sustainable drainage systems, contribute to air quality and carbon sequestration, mitigate urban heat island, support biodiversity, and create green spaces supporting public well-being. Bus stops provide good opportunities for installing green roofs. 

  • blue-green cities
  • ecosystem services
  • green infrastructure
  • cost benefit analysis
  • green roof

1. Introduction

The installation of green roofs (GRs) in cities contributes to the development of a healthy blue-green infrastructure network [1], which is indispensable for sustainable urban development [2][3]. GRs are partially or fully vegetated roofs that extend the conventional roof by a waterproof membrane (with the possible addition of a root barrier), a drainage layer, a filter layer, a lightweight substrate, and vegetation (Figure 1) [4].
Land 12 01831 g001
Figure 1. Structure of a typical green roof.
The fundamental division of GRs according to substrate depth and plant species recognises extensive (EGRs) and intensive green roofs (IGRs). EGRs are specified by shallow mineral-based substrate supporting low plants such as Sedum spp., moss, wildflowers, or grass, which make them well-suited for bus shelter applications. Bus shelters provide unused roof spaces that can be transformed into additional green urban infrastructure. This research gives a brief overview of the benefits provided by EGRs. It presents a case study comparing the benefits and costs of their installation on bus shelters in Edinburgh.

2. Benefits of Green Roofs in the Urban Context

GRs provide a number of environmental and social benefits. Substrate and vegetation are the essential and the most understood structural layers of GRs regarding the benefit provided.
Substrate captures rainwater, reduces the runoff volume, and delays its peak. Warmer and wetter weather with increased heat islands and frequent heavy rainfalls is predicted for the east of Scotland. Between 1981–2010, the frequency of heavy rainfalls increased by 5% compared to the years 1961–1990 [5]. GRs applied on roofs in urban areas have an essential role in Sustainable Drainage Systems (SuDS), being one of the leading stormwater management solutions [1][4][6][7]. GRs in urban settings can simultaneously achieve three main aims of SuDS—reduce the quantity of runoff and delay its peak, improve runoff quality, and provide good amenity values [6][8][9][10][11].
Vegetation is also essential in erosion prevention and evapotranspiration, providing a greater surface and influencing initial substrate moisture [12][13][14]. The vegetation layer mitigates urban heat island (UHI) through increased evapotranspiration, increased albedo, and reduced direct sensible heat emissions [15][16]. Roads are among the hottest areas in cities due to their low albedo [17][18][19]. It has been concluded that GRs might be more efficient when their height is lower than 10 m [20], making city bus stops an ideal location.
The green roof hydrological cycle is prosperous for both stormwater management and evapotranspiration’s cooling effects [21]. According to various authors, the water content in soil is the strongest factor for evapotranspiration [22][23][24][25][26]. Feng et al. [27] found that increased water content in the substrate from 30% to 60% reduced heat stored in GR by 24%. This agreed with studies by Coutts et al. [28] and Wong et al. [20], showing limited evapotranspiration rates and cooling effects of GRs after a dry period. Water content in leaves may also cause higher reflectance [29].
In addition, the vegetation layer improves air quality by direct pollutant sequestration and lowering air temperature, which results in a reduction in air pollution creation, thus preventing ozone formation [4]. Plants provide a surface area for the wet and dry deposition of pollutants [30][31]. Particles that are not captured by leaves can be absorbed by cuticle digestion, stomata penetration, or deposited in soil and absorbed by roots [32][33][34]. Gaseous pollutants are sequestered by vegetation through their stomata [34]. The roof type and planted vegetation also control the sequestration of CO2 [35]. Generally, GRs can reduce CO2 through direct sequestration or indirect shading effect and evapotranspiration, lowering ambient air temperature and electricity demand [36].
One of the main reasons for GR installation in urban areas is the creation of new habitats and biodiversity support. With the spread of GRs in the 20th century, more profound research focused on their design, rainwater retention, and insulation benefits. However, there is still a lack of studies targeting GRs’ importance in biodiversity, habitat support, and the long-term monitoring of fauna and flora behaviour and establishment [37][38]. Together with the substrate layer, the vegetation layer creates new habitats for lost urban biodiversity and supports pollinators [1], which are threatened by the expansion of urban conglomerates [7]. Furthermore, it can ease the movement of wildlife and deliver measurable biodiversity net gain (BNG) [39]. This is especially vital in the context of new policies requiring 10% of BNG in any new urban planning project in the UK [40].
In addition to all of the environmental benefits GRs deliver, improving previously unused roofs makes people happy and more inclined to care about nature [41]. GRs have an important role in adding aesthetics to highly built-up areas and increasing the value of surrounding properties by 9% [42]. Furthermore, therapeutic benefits were measured from flower terpenes, colours, and sound variations that GRs provide [39][43]. One of the main barriers to implementing GRs is the lack of public knowledge [44]. However, when implemented, GRs in urban areas might be a great opportunity to raise awareness of their benefits and encourage further implementation [45].

3. Summarycope offor the Case Study

Different cities have adopted the law of implementing at least partially vegetated roofs on new buildings [46]. Utrecht was the first city to implement green bus shelters, installing 316 of them. Different cities in the Netherlands (Haarlem, Gouda, Apeldoorn, Woerden, Wageningen), Leipzig in Germany, and Helsingborg and Malmö in Sweden are following this trend. In the UK, Leicester has installed 30 GRs on bus shelters; Milton Keynes, Manchester, Newcastle, Cardiff, Oxford, and Brighton have installed GRs on some of the bus shelters as well (Figure 2) [47]. The majority of these projects are funded by grants and funds with no additional costs to the city councils [48].
Land 12 01831 g002
Figure 2. Green bus stops across cities: (a) Utrecht [49], (b) Leicester [48], (c) Manchester [50], (d) Milton Keynes (Ch. Bridgman, personal communication, 21 January 2022).
Despite the global expansion of GRs integration into urban architecture, there is a lack of studies based on solid scientific analysis of the costs and benefits involved [1], which was identified as the main knowledge gap. This research’s objective is to provide a comparison of the costs and benefits of EGRs application in the City of Edinburgh with suggestions for its green future as part of the City Plan 2030. The results of the research show that the application of EGRs on bus shelters in Edinburgh would have the highest benefit value in education, amenity value and lowering air pollution, and may outweigh the associated costs. This will help the city transition to net-zero carbon emissions by 2030 and contribute to the creation of thriving green spaces as part of Edinburgh’s 2050 city vision [51]. Moreover, it will benefit initiatives such as Cleaner Air for Scotland—The Road to a Healthier Future [52] and bring opportunities for increasing BNG in new and existing infrastructure.

References

  1. Miller, K.; Krivtsov, V.; Cohen, L. Inventory of Green Roofs within Edinburgh, Scotland. In CIGOS 2021, Emerging Technologies and Applications for Green Infrastructure. Lecture Notes in Civil Engineering; Springer: Singapore, 2022; pp. 1345–1353.
  2. Krivtsov, V.; Arthur, S.; Allen, D.; O’Donnell, E. Blue-Green Infrastructure–Perspectives on Planning, Evaluation and Collaboration; CIRIA: London, UK, 2019.
  3. Arthur, S.; Krivtsov, V.; Allen, D.; Ahilan, S.; Guan, M.; Haynes, H.; Sleigh, A.; Wright, N. Blue-Green Infrastructure–Perspectives on Water Quality Benefits; CIRIA: London, UK, 2019.
  4. EPA. Estimating the Environmental Effects of Green Roofs: A Case Study in Kansas City, Missouri; EPA: Washington, DC, USA, 2018; p. 26.
  5. Partnership, T.E. Resilient Edinburgh-Climaze Change Adaptation Framework For Edinburgh 2014–2020; Evidence Base and Risk Analysis; The Edinburgh Partnership: Edinburgh, UK, 2012.
  6. Stovin, V.; Poë, S.; Berretta, C. A modelling study of long term green roof retention performance. J. Environ. Manag. 2013, 131, 206–215.
  7. Sutton, R.K. Introduction to Green Roof Ecosystems. In Green Roof Ecosystems; Sutton, R.K., Ed.; Springer International Publishing: Cham, Switzerland, 2015; pp. 1–25.
  8. DeNardo, J.C.; Jarrett, A.R.; Manbeck, H.B.; Beattie, D.J.; Berghage, R.D. Stormwater mitigation and surface temperature reduction by green roofs. Trans. ASAE 2005, 48, 1491–1496.
  9. VanWoert, N.; Rowe, D.; Andresen, J.; Rugh, C.; Fernandez, R.; Xiao, L. Green Roof Stormwater Retention: Effects of Roof Surface, Slope, and Media Depth. J. Environ. Qual. 2005, 34, 1036–1044.
  10. Carter, T.L.; Rasmussen, T.C. Hydrologic Behavior of Vegetated Roofs1. JAWRA J. Am. Water Resour. Assoc. 2006, 42, 1261–1274.
  11. Nawaz, R.; McDonald, A.; Postoyko, S. Hydrological performance of a full-scale extensive green roof located in a temperate climate. Ecol. Eng. 2015, 82, 66–80.
  12. Gong, Y.; Zhang, X.; Li, H.; Zhang, X.; He, S.; Miao, Y. A comparison of the growth status, rainfall retention and purification effects of four green roof plant species. J. Environ. Manag. 2021, 278, 111451.
  13. Soulis, K.X.; Ntoulas, N.; Nektarios, P.A.; Kargas, G. Runoff reduction from extensive green roofs having different substrate depth and plant cover. Ecol. Eng. 2017, 102, 80–89.
  14. Stovin, V.; Poë, S.; De-Ville, S.; Berretta, C. The influence of substrate and vegetation configuration on green roof hydrological performance. Ecol. Eng. 2015, 85, 159–172.
  15. Hamilton, I.; Stocker, J.; Evans, S.; Davies, M.; Carruthers, D. The impact of the London Olympic Parkland on the urban heat island. J. Build. Perform. Simul. 2014, 7, 119–132.
  16. United States Environmental Protection Agency. Heat Island Impacts. June 2014. Available online: https://www.epa.gov/heatislands/heat-island-impacts (accessed on 10 April 2022).
  17. Carpentieri, M.; Kumar, P.; Robins, A. An overview of experimental results and dispersion modelling of nanoparticles in the wake of moving vehicles. Environ. Pollut. 2011, 159, 685–693.
  18. Yang, J.; Wang, Y.; Xiu, C.; Xiao, X.; Xia, J.; Jin, C. Optimizing local climate zones to mitigate urban heat island effect in human settlements. J. Clean. Prod. 2020, 275, 123767.
  19. Zhu, R.; Wong, M.S.; Guilbert, É.; Chan, P.-W. Understanding heat patterns produced by vehicular flows in urban areas. Sci. Rep. 2017, 7, 16309.
  20. Wong, N.H.; Chen, Y.; Ong, C.L.; Sia, A. Investigation of thermal benefits of rooftop garden in the tropical environment. Build. Environ. 2003, 38, 261–270.
  21. Cascone, S.; Arpón, J.C.; Gagliano, A.; Luque, G.P. The evapotranspiration process in green roofs: A review. Build. Environ. 2019, 147, 337–355.
  22. Jim, C.Y.; Peng, L.L.H. Weather effect on thermal and energy performance of an extensive tropical green roof. Urban For. Urban Green. 2012, 11, 73–85.
  23. Liu, K.; Minor, J. Performance Evaluation of an Extensive Green Roof; Presentation at Green Rooftops for Sustainable Communities: Washington, DC, USA, 2005; p. 14.
  24. Pérez, G.; Vila, A.; Solé, C.; Coma, J.; Castell, A.; Cabeza, L.F. The thermal behaviour of extensive green roofs under low plant coverage conditions. Energy Effic. 2015, 8, 881–894.
  25. Susca, T.; Gaffin, S.R.; Dell’Osso, G.R. Positive effects of vegetation: Urban heat island and green roofs. Environ. Pollut. 2011, 159, 2119–2126.
  26. Tsang, S.W.; Jim, C.Y. Theoretical evaluation of thermal and energy performance of tropical green roofs. Energy 2011, 36, 3590–3598.
  27. Feng, C.; Meng, Q.; Zhang, Y. Theoretical and experimental analysis of the energy balance of extensive green roofs. Energy Build. 2010, 42, 959–965.
  28. Coutts, A.M.; Daly, E.; Beringer, J.; Tapper, N.J. Assessing practical measures to reduce urban heat: Green and cool roofs. Build. Environ. 2013, 70, 266–276.
  29. He, H.; Jim, C.Y. Simulation of thermodynamic transmission in green roof ecosystem. Ecol. Model. 2010, 221, 2949–2958.
  30. Bottalico, F.; Chirici, G.; Giannetti, F.; De Marco, A.; Nocentini, S.; Paoletti, E.; Salbitano, F.; Sanesi, G.; Serenelli, C.; Travaglini, D. Air Pollution Removal by Green Infrastructures and Urban Forests in the City of Florence. Agric. Agric. Sci. Procedia 2016, 8, 243–251.
  31. Hill, A.C. Vegetation: A sink for atmospheric pollutants. Environ. Pollut. 2017, 231, 207–218.
  32. Cai, M.; Xin, Z.; Yu, X. Spatio-temporal variations in PM leaf deposition: A meta-analysis. Environ. Pollut. 2017, 231, 207–218.
  33. Currie, B.; Bass, B. Estimates of air pollution mitigation with green plants and green roofs using the UFORE model. Urban Ecosyst. 2008, 11, 409–422.
  34. Speak, A.F. Quantification of the Environmental Impacts of Urban Green Roofs’. The University of Manchester. School of Environment and Development. 2013. Available online: https://www.research.manchester.ac.uk/portal/files/54539943/FULL_TEXT.PDF (accessed on 20 April 2022).
  35. Zakrisson, A. Green Roof CO2 Capture Explained. Purple-Roof. 2021. Available online: https://www.purple-roof.com/post/green-roof-co2-capture-explained (accessed on 15 April 2022).
  36. Kuronuma, T.; Watanabe, H.; Ishihara, T.; Kou, D.; Toushima, K.; Ando, M.; Shindo, S. CO2 Payoff of Extensive Green Roofs with Different Vegetation Species. Sustainability 2018, 10, 2256.
  37. Köhler, M.; Ksiazek-Mikenas, K. Chapter 3.14-Green Roofs as Habitats for Biodiversity. In Nature Based Strategies for Urban and Building Sustainability; Pérez, G., Perini, K., Eds.; Butterworth-Heinemannl: Oxford, UK, 2018; pp. 239–249.
  38. Thuring, C.; Grant, G. The Biodiversity of temperate extensive green roofs: A review of research and practice. Isr. J. Ecol. Evol. 2015, 62, 44–57.
  39. GRO. The GRO Green Roof Code. Green Roof Organisation. 2021. Available online: https://www.greenrooforganisation.org/wp-content/uploads/2021/03/GRO-Code-2021-Anniversary-Edition.pdf (accessed on 11 April 2022).
  40. PAS. Biodiversity Net Gain|Local Government Association. Available online: https://www.local.gov.uk/pas/topics/environment/biodiversity-net-gain (accessed on 19 April 2022).
  41. Prijs, M. Green-Roofed Bus Shelters|Closer Cities’, Closer Cities. 2020. Available online: https://closercities.org/projects/green-roofed-bus-shelters#no-back (accessed on 20 April 2022).
  42. Tomalty, R.; Komorowski, B. The Monetary Value of the Soft Benefits of Green Roofs; Smart Cities Research Services: Montreal, QC, Canada, 2010.
  43. GSA. The Benefits and Challenges of Green Roofs on Public and Commercial Buildings. A Report of the United States General Services Administration. 2011. Available online: https://www.gsa.gov/cdnstatic/The_Benefits_and_Challenges_of_Green_Roofs_on_Public_and_Commercial_Buildings.pdf (accessed on 20 April 2022).
  44. Andreoni, V.; Payne, K.; Sullivan, O. Promoting the Use of Green Roofs on Street-Level Surfaces to Improve Public Awareness about Stormwater Management in Boston. 2013. Available online: https://web.wpi.edu/Pubs/E-project/Available/E-project-101713-170426/unrestricted/Street-Level_Green_Roofs_to_Promote_Stormwater_Awareness.pdf (accessed on 20 April 2022).
  45. ScienceToGo.org. ScienceToGo.org-Climate Change Awareness Boston, Science To Go. Available online: https://sciencetogo.org (accessed on 25 April 2022).
  46. Márquez, M.I.V. Effectiveness of Green Roofs and Walls to Mitigate Atmospheric Particulate Matter Pollution in a Semi-Arid Climate. Pontificia un iversidad Catolica de Chile. School of Engineering. 2021. Available online: https://repositorio.uc.cl/xmlui/bitstream/handle/11534/61934/tesis%20MViecco11agosto_compressed.pdf (accessed on 20 April 2022).
  47. USGS. Runoff: Surface and Overland Water Runoff|U.S. Geological Survey. 2018. Available online: https://www.usgs.gov/special-topics/water-science-school/science/runoff-surface-and-overland-water-runoff?qt-science_center_objects=0#overview (accessed on 19 March 2022).
  48. ClearChannel. “Bee Bus Stops” Springing up in Leicester|Clear Channel UK. 2021. Available online: https://www.clearchannel.co.uk/latest/bee-bus-stops-springing-up-in-leicester (accessed on 30 April 2022).
  49. SemperGreen. Green Bus Stops Ensure a Future-Proof City-Sempergreen. 2019. Available online: https://www.sempergreen.com/en/about-us/news/green-bus-stops-ensure-a-future-proof-city (accessed on 30 April 2022).
  50. JCDecaux. State of the Art Bus Shelters for Manchester|JCDecaux UK. 9 November 2016. Available online: https://www.jcdecaux.co.uk/state-art-bus-shelters-manchester (accessed on 30 April 2022).
  51. Murphy, S. Thriving Green Spaces Project, The City of Edinburgh Council. Available online: https://www.edinburgh.gov.uk/parks-greenspaces/thriving-green-spaces-project (accessed on 19 April 2022).
  52. EFD. Cleaner air for Scotland: The Road to a Healther Future. List of Actions, gov.scot. 2015. Available online: http://www.gov.scot/publications/cleaner-air-scotland-road-healthier-future/pages/17/ (accessed on 26 April 2022).
More
© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)
Video Production Service
Feedback