How can Green Infrastructure Uptake Improve Urban Environmental Conditions Triggered by Climate Change?
ABout the Author/s
L’Afrique est de plus en plus touchée par les effets néfastes du changement climatique, tels que de graves inondations, des vagues de chaleur et des sécheresses prolongées. En outre, les villes africaines sont confrontées à une urbanisation rapide, entraînant la fragmentation et la dégradation des espaces verts urbains. Les autorités municipales sont chargées de protéger et de conserver les espaces verts urbains, mais les villes africaines sont confrontées à des urgences socio-économiques complexes qui priment sur les questions vertes. Les architectes paysagistes sont bien placés et équipés pour promouvoir activement l'atténuation des impacts du changement climatique dans les zones urbaines en améliorant délibérément les infrastructures vertes dans leurs solutions de conception. La fonction de refroidissement de la végétation dans les zones urbaines et la réduction des inondations sont deux solutions fondées sur la nature qui peuvent améliorer les conditions environnementales urbaines causées par le changement climatique. Deux exemples de projets en Afrique australe sont présentés : 1) une étude menée à Bulawayo, au Zimbabwe, démontre l'effet rafraîchissant de la température de l'air ambiant par la verdure urbaine et les économies qui en résultent sur les coûts énergétiques grâce à une utilisation réduite de la climatisation par les bâtiments environnants ; 2) un projet à Johannesburg, en Afrique du Sud, découvre et naturalise un canal d'eaux pluviales urbaines. La réhabilitation du ruisseau a permis de restaurer le fonctionnement écologique des habitats environnants, la capacité d'infiltration de l'espace vert, tout en offrant des installations récréatives aux résidents et en améliorant le bien-être humain.
Africa is increasingly affected by the adverse effects of climate change, such as severe flooding events, heat waves, and prolonged droughts. In addition, African cities face rapid urbanisation, leading to the fragmentation and degradation of urban green spaces. City officials are tasked with protecting and conserving urban green space, but African cities face complex socio-economic urgencies that take precedence over green issues. Landscape architects are well-positioned and equipped to actively promote mitigating climate change impacts in urban areas by purposefully enhancing green infrastructure in their design solutions. The cooling function of vegetation in urban areas and flood alleviation are two nature-based solutions that can improve the urban environmental conditions caused by climate change. Two project examples in Southern Africa are shown: 1) a study in Bulawayo, Zimbabwe, demonstrates the cooling effect of ambient air temperature by urban greenery and the subsequent savings in energy costs due to reduced use of air conditioning by surrounding buildings; 2) a project in Johannesburg, South Africa, uncovers and naturalises an urban stormwater channel. The rehabilitation of the stream has restored the ecological functioning of surrounding habitats and the infiltration capacity of the green space while providing recreational facilities for residents and improved human well-being.
Introduction
As landscape architects who focus on green space planning and design, we feel certain that landscape design improves the world for humans and other species. This ethos of ‘joint concern for the planet’ that landscape architects share was made public when the International Federation for Landscape Architects (IFLA) 2019 launched a “climate and biodiversity action plan” to increase sustainability in landscape design and commit members to “work with national associations to alter our ethical standards and codes of conduct”. This call was mainly driven by the increased awareness and concern for climate change.
Globally, scientists believe integrating green infrastructure in urban planning can reduce environmental hazards exacerbated by climate change while creating sociocultural benefits. This is important for Africa since Sub-Saharan Africa is reportedly warming up 1.5 times faster than the global average. But how exactly does green space or infrastructure combat these environmental hazards?
What can “green interventions” really do to combat climate change?
Flood hazards and the urban heat island effect are the key urban climate change hazards we face and are highly relevant to green infrastructure functions and human social well-being (Li et al., 2022). The cooling and hydrological regulation functions of vegetation and water bodies help reduce thermal exposure and flood risk to urban residents while enhancing recreation and urban environmental amenities (Tzoulas et al., 2010). The cooling function of vegetation and water bodies consists of two main aspects. Firstly, vegetation transpiration and evaporation from the water surface increase the net latent heat flux and reduce the net sensible heat flux in urban areas. Secondly, the shading effect of vegetation reduces the net radiant heat incident to the surrounding urban surface, thus reducing the surface temperature. In a rainfall event, the hydrological processes of interception, infiltration into vegetation, stagnation, evapotranspiration, and the confluence of water bodies can effectively regulate surface runoff.
Vegetation and water bodies also provide social benefits regarding recreation, health, and economic functions. The benefit level to humans varies significantly and equitably with the spatial heterogeneity of available and accessible green space and infrastructure. This influences residents’ disaster exposure levels to extreme weather events and residents’ physical and mental health (Wu et al., 2016).
What does this mean for Africa?
Cities in sub-Saharan Africa are facing rapid urbanisation and challenges with the degradation of existing green spaces, and their vulnerability to climatic risks is increasing daily. These trends stress the already over-capacitated, often poorly maintained urban infrastructure services.
It is often suggested that authorities integrate the support and regeneration of urban ecosystems into urban infrastructure development to make cities more resilient and sustainable. However, socio-economic urgencies and political agendas often overshadow green infrastructure opportunities in sub-Saharan Africa. City officials face many complex challenges with applying green infrastructure, such as poor intergovernmental collaboration, conflicting spatial and environmental policies, regulations and frameworks, scarce resources, housing shortages resulting in land invasions, and a lack of appreciation of the value and benefits that green infrastructure can provide.
What can be done?
Despite the challenges, many opportunities for improved green infrastructure planning and application exist in sub-Saharan Africa, such as streamlining the land development application process, incentivising developers, enabling cross-sectoral partnerships to open new resource pools to fund green infrastructure applications, and promoting the long-term benefits of green infrastructure. The value of local cross-sectoral input in green infrastructure planning and nature-based solutions co-development cannot be over-emphasised (Du Plessis, 2024).
‘Nature-based solutions’ (NbS) is the latest green infrastructure concept and can be broadly defined as “actions to protect, conserve, restore, sustainably use and manage natural or modified terrestrial, freshwater, coastal and marine ecosystems, which address social, economic and environmental challenges effectively and adaptively, while simultaneously providing human well-being, ecosystem services and resilience and biodiversity benefits” (UNEA, 2022).
Do we have any good local examples of NbS to offer?
Identifying solutions from nature is not necessarily novel, but promoting these services and their purposeful support and funding is critical.
A study in Bulawayo, Zimbabwe (Ngulani & Shackleton, 2020) shows that urban greenery can mitigate the urban heat island effect by cooling the ambient air temperature by up to 6.1°C in summer and 5.7°C in winter.
Cooler air temperatures were experienced up to a radius of 1.7km from the green spaces. The study effectively illustrates a reduced energy cost of air conditioning in the buildings surrounding the park to approximately US$532/household/yr.
Another example is Paterson Park in Johannesburg, South Africa.[1] Stormwater runoff channelled and buried beneath the park in the 1940s was uncovered and naturalised when the channel started collapsing. In addition, the infrastructure's capacity was inadequate to contain the increased volume of stormwater due to urbanisation. The rehabilitation of the channel has resulted in ecological, social, and engineering benefits such as improved filtration and habitat functions, walkways, play areas, additional tree species, which sequestrate carbon emissions and cool the area, decreased velocity of runoff and a fourfold increased stormwater retention capacity.
What is the way forward?
Nature-based solutions cannot be blindly considered as the only antidote for climate change.
The changing climatic conditions can negatively impact the vegetative species used in landscape projects if areas become drier and hotter in the future, which is already experienced in various parts of the world, such as Europe. So, the purposeful (re)selection of species becomes a very important consideration, as seen in various current studies in the global north. In addition, in the global south, we must also remember that other infrastructures, such as access to potable water, energy, health services and sanitation, can equally affect human well-being in the face of climate change and associated risks. Therefore, green infrastructure cannot be considered in isolation.
We argue that landscape architects and other built-environment professionals involved in urban development are morally obligated to actively promote the application of appropriate green infrastructure and nature-based solutions (together with social and technological solutions) to mitigate the effects of climate change in urban areas. Responsible designers can no longer turn a blind eye to seas of impermeable surfaced parking areas with minimum tree cover, homogeneous planting palettes, and irrigation systems connected to municipal potable water.
“One only realises the importance of a well when the water dries up” (African Proverb).
Follow our work in the international research project:
Collaboration on Nature-based Solutions for Sustainable Cities (CONSUS): https://consusresearch.weebly.com/
References
[1] Professional team: Chris Brooker of CBA Specialist Engineering and Landscape Architects, Karien Hanekom of KHLA & Johan Barnard of NLA.
Further Reading
Cortinovis, C., Olsson, P., Boke-Olén, N., & Hedlund, K. (2021). Scaling up nature-based solutions for climate-change adaptation: Potential and benefits in three European cities. Urban Forestry & Urban Greening, 67, 127450. https://doi.org/10.1016/j.ufug.2021.127450
Haase, D. & Hellwig, R. (2022). Effects of heat and drought stress on the health status of six urban street tree species in Leipzig, Germany. Trees, Forests and People, Volume 8, 100252, ISSN 2666-7193, https://doi.org/10.1016/j.tfp.2022.100252.
Hanzl, M., Tofiluk, A., Zinowiec-Cieplik, K., Grochulska-Salak, M., & Nowak, A. (2021). The Role of Vegetation in Climate Adaptability: Case Studies of Lodz and Warsaw. Urban Planning., Lisbon 6(4), 9-24. DOI:10.17645/up.v6i4.3931
Hobbie, S.E. & Grimm, N.B. (2020). Nature-based approaches to managing climate change impacts in cities. Philosophical Transactions of the Royal Society B. 375: 20190124. http://doi.org/10.1098/rstn.2019.0124
Li X, Stringer L, Dallimer M. (2022). The role of blue green infrastructure in the urban thermal environment across seasons and local climate zones in East Africa[J]. Sustainable Cities and Society, 80:103798.
Ngulani, T. & Shackleton, C.M. (2020) The degree, extent, and value of air temperature amelioration by urban green spaces in Bulawayo, Zimbabwe, South African Geographical Journal, 102(3), 344-355, DOI: 10.1080/03736245.2019.1685405
Tzoulas K, James P. (2010). Peoples’ use of, and concerns about, green space networks: A case study of Birchwood, Warrington New Town, UK[J]. (2010). Urban Forestry & Urban Greening, 9, 121-128.
United Nations Environment Assembly. (2022). Nature-based solutions for supporting sustainable development: Resolution adopted by the United Nations Environment Assembly on 2 March 2022. UNEP. Retrieved 25 January from https://wedocs.unep.org/handle/20.500.11822/39752
Wu J, Si M, Li W. (2016). Spatial equity analysis of urban green space from the balance Between supply and demand perspective: A case study of Futian District, Shenzhen, China[J]. Chinese Journal of Applied Ecology, 27(09), 2831-2838.
