Urban Greening: A blueprint for environmental resilience
Dr. Alka Singh
Climate change is having a significant impact with threatening influence on urban environment with cumulative urbanization, posing challenges for the urban ecosystem. Rapid urbanization accompanied with degraded urban environment and population explosion estimated at 1.42 billion inhabitants in India, account to approximately 17.31% of the global population. The rapid urbanization that has accompanied this demographic shift poses significant challenges in the realms of environmental sustainability.
Currently, nearly 40% of India’s population resides in urban locales, a figure projected to soar to 60% by 2050. This urban expansion is not without its drawbacks; it has led to escalating issues of air pollution and overpopulation, adversely affecting public health, well-being and overall quality of life. Moreover, the rapid growth of sprawling cities has resulted in the proliferation of vulnerable urban communities residing in informal settlements. These communities contribute to intensified environmental stress, marked by compromised indoor and outdoor air quality.
Furthermore, urban regions are increasingly becoming hotspots for climate change risks, as they are significant contributors to global greenhouse gas emissions. In this evolving landscape, urban greening, the practice of integrating plant life into urban environments, offers a beacon of hope with offering avenues for improved air quality and enhanced community well-being. The tormenting issues in urban areas extend beyond individual human health to encompass a complex web of interrelated factors such as psychological well-being, community health and happiness along with environmental sustainability.
In the face of the escalating challenges of urban life ranging from air and noise pollution to the mental health toll of living in overcrowded conditions, greening of the urban ecosystem can serve as a holistic solution by improving air quality, reducing the urban heat island effect, and promoting biodiversity along with therapeutic effects. As we understand the complexities of urban living, integrating urban greening into our strategies for healthier indoor environments is not just an option; it’s a necessity.
Urban Environment: Pollution and Climate Risk
The impact of climate change is high in urban areas and urban environment has been constantly degrading. A massive proportion of both the global population and economic activities are concerted in urban areas, making them vulnerable to the impacts of climate change. Moreover, cities are major contributors to global greenhouse gas emissions, further aggravating the climate crisis. Air pollution is a particularly adamant issue in Indian cities, where Suspended Particulate Matter (SPM) is a major pollutant. This is primarily due to the escalating count of automobiles, inadequate traffic control, and congested roads, coupled with industrial activities in peri-urban areas.
Pollutants such as Particulate Matter (PM), Nitrogen Dioxide (NO2), Sulphur Dioxide (SO2), and Carbon Dioxide (CO2) are consistently degrading the air quality, often exceeding the limits set by the World Health Organization (WHO). WHO data show that almost all of the global population (99%) breathe air that exceeds WHO guidelines. According to the WHO reports, 6.7 million deaths each year globally occur owing to air pollution, making it the world’s largest single environmental health risk. The report highlighted that low- and middle-income countries, particularly in South-East Asia and the Western Pacific Regions, bore the brunt of this burden.
Alarmingly, the number of deaths linked to air pollution could rise to 5 billion by 2030 worldwide. Recent studies indicate that a significant population in the Indian subcontinent is exposed to air with Particulate Matter (PM2.5) levels far exceeding WHO guidelines. In 2013, the International Agency for Research on Cancer (IARC), a WHO affiliate, classified outdoor air pollution, especially particulate matter, as a Class-1 carcinogen. Besides threatening cancer, it is also linked to other respiratory and heart diseases. Recent data reveals a grim picture: India is one among the ten most polluted countries with fifth rank in the world and out of the 10 most polluted cities in the world, 7 are in India.
Urban areas are increasingly becoming complex ecosystems with unique challenges, particularly in the context of climate change and environmental degradation. One such challenge is the urban heat island (UHI) effect, aggravated by large, impermeable surfaces and densely packed buildings, disrupting of natural drainage channels and accelerating runoff. Approximately 40-50% of impermeable surfaces in urban areas consist of unused roof space.
These impermeable surfaces contribute to varying levels of annual runoff, ranging from 0% in water surfaces, forests, and public parks, to as high as 90% in roads, parking areas, and buildings. This runoff often carries pollutants, which are then discharged untreated into local water bodies, further aggravating environmental concerns. The UHI occurs due to the absorption and later re-radiation of solar energy by physical structures in urban areas. The UHI effect not only increases temperatures in urban centers but also has a cascading impact on greenhouse gas emissions. When the additional demand for cooling is met with electricity generated from fossil fuels, the cycle of environmental degradation intensifies. The implications of these challenges are far-reaching. The UHI effect and poor water management contribute to a vicious cycle of environmental degradation and climate change, making the need for sustainable solutions like Urban Greening even more critical.
Further, indoor air pollution has emerged as a silent yet compelling crisis of urban life. While much attention is focused on outdoor air pollution, the quality of indoor air within homes, offices, and other facilities is often overlooked, despite its significant impact on public health. Indoor air pollution is particularly concerning in urban settings where energy-efficient measures can sometimes make indoor environments relatively airtight. This reduced ventilation can lead to elevated levels of pollutants, creating a host of health issues. According to the Institute for Health Metrics and Evaluation (IHME), an alarming 2.6 million people died prematurely in 2016 due to illnesses linked to household air pollution. The primary sources of indoor air pollution are the inefficient use of solid fuels for cooking and heating. Surprisingly, more than 2.3 billion people in developing countries still rely on solid fuels like wood, crop waste, charcoal, coal, and dung for their daily cooking and heating needs.
These are often burned in open fires or leaky stoves, leading to hazardous indoor air quality. A report by the World Health Organization (WHO) equates the smoke inhaled by women from such unclean fuel to the harmful effects of smoking 400 cigarettes in an hour. In the web of urban life, the concern of indoor air pollution has become increasingly complex. The shift towards more tightly sealed buildings, reduced ventilation, and the use of synthetic materials in construction and furnishing have all contributed to deteriorating indoor air quality. Besides, the dominance of chemical products, pesticides, and household care items further aggravates the problem. Thus, indoor air pollution is a silent killer, often going unnoticed as it doesn’t always produce immediate, recognizable health impacts. The pollutants range from particulates, carbon monoxide, and polycyclic organic matter to formaldehyde, commonly found in carpets, particle boards, and insulation foams. Other pollutants like nitrogen dioxides, carbon monoxide, and lead also compromise indoor air quality.
In some poorly ventilated buildings, asbestos and radon become additional cause of air quality concern. The concern is further complicated in modern offices and new homes designed with tighter construction to seal the building from outside air, inadvertently raising indoor air pollutants to dangerous levels, posing a significant health risk to urban dwellers.
Environmental rewards of greening cities
Greening the cities offers manifold environmental benefits besides addition of the green aesthetics. This is particularly crucial in a time when cities are struggling with the hostile effects of climate change and air pollution. Elevated green spaces in urban vicinity also contribute to the city’s overall environment by reducing heat islands, improving air quality, and promoting biodiversity. Trees and shrubs sequester atmospheric carbon dioxide and thereby reduce the urban carbon footprint. Innovation in landscaping concepts have evolved to include green buildings, green belts, and green roofs, all aimed at energy conservation and environmental sustainability.
These features not only beautify urban spaces but also serve functional roles in mitigating various forms of pollution i.e, air, sound, water and soil. The choice of specific plants can be custom-made to address these environmental challenges, making urban greenscaping a strategic tool in urban planning. Parks and urban green spaces offer more than just recreational benefits; they are essential for public health. They provide accessible and affordable venues for physical activity, thereby contributing to the well-being of urban residents. Urban greening can considerably mitigate the urban heat island effect.
Living vegetation on building walls and roofs acts as a natural insulator, reducing solar radiant heating, especially during the sweltering summer months. This, in turn, decreases the demand for mechanical cooling, leading to reduced electricity consumption and, consequently, lower greenhouse gas emissions. As cities continue to expand and face increasing environmental challenges, the role of urban greening in improving ecological and environmental services becomes even more critical. Plants act as natural air purifiers, absorbing pollutants and improving indoor air quality.
Studies have also shown that green infrastructure can have a positive impact on microclimates, particularly in alleviating the urban heat island effect in hot and humid summers. The strategic greening of urban spaces, through parks, tree plantations, green roofs, and walls, can significantly reduce both water and air pollution. This, in turn, mitigates health risks for both people and wildlife, enhances biodiversity, and improves overall environmental health. Thus, the environmental benefits of urban greening are not just an add-on; they are essential for sustainable urban living.
Alleviation of urban pollution
Greening of the urban spaces with trees can play a major role in moderation of urban pollution. Tree plantation even in smaller groups, avenues and isolated trees can equally improve environmental conditions in urban areas. Besides, it also helps in soil-moisture retention; prevent erosion, modifying air temperature, creating microclimate and removal of noise and dust pollution. It also provide habitat for birds and animals.
A landform devoid of vegetation show erosive rate of around 500 tons/m2/year. A green belt planting of around 180-200 m can reduce airborne particulate matter by as much as 75 percent. Trees contribute in noise abatement. Trees can reduce 7db noise per 100 feet by reflecting and absorbing sound energy. Besides, trees provide “white noise”, the noise of the leaves and branches in the wind and associated natural sounds, that mask other man-caused sounds. Dust filtering capacity of trees is also very important. Evergreen tree species, and in particular conifers, filter more dust than deciduous species. Further, trees contribute in glare reduction on road sides as they help control light scattering, light intensity, and modify predominant wavelengths on a site, this help to minimize eye strain for safety and visibility.
Trees with blooming flowers
Trees can be rightly termed as ‘oxygen banks’ for human beings especially in urban life. However, with high level of pollutants in air even the growth of plants becomes stunted and becomes difficult for survival. Some tree species are highly tolerant to air pollution. Such trees can function as biological filters & cleanse the atmosphere.
Some of the tree species like Albizzia lebbeck, Alstonia scholaris, Butea monosperma, Ficus benjamina, Madhuca indica, Pongamia glabra, Lagerstroemia flos-reginae, Ficus religiosa, Peltophorum pterocarpum & Terminalia arjuna can be planted in industrial areas since they are tolerant to dust and smoke. As per a study at Navsari, Thevetia peruviana has been found to be highly resistant to environmental pollution. Ficus species also score high in pollution tolerance. For noise reduction Mangifera indica, Butea monosperma, Madhuca indica, Terminalia arjuna, Alstonia scholaris and Azadirachta indica are very suitable.
Management of urban heat
Greening of the urban vicinity specially with trees play major role in temperature regulation in urban life. Greenery can directly cool urban areas by shading heat-absorbing surfaces and indirectly through the process of evapotranspiration. To put this into perspective, a single tree can transpire up to 40 gallons of water in a day, offsetting the heat produced by one hundred 100-watt lamps operating for eight hours. In urban areas, where vegetation is limited, buildings and paved surfaces absorb energy from the sun, causing the surface temperature of urban structures to become 1–3°C higher than the ambient air temperatures. Further, the overall ambient air temperature also increases, resulting in “urban heat island” that raises air temperature in a city by 1.1–4.5°C.
Vegetated areas specially with trees provide relief from the ‘heat island effect’. It has been known that air under a tree’s canopy can be as much as 5-100F cooler compared to barren location. The average temperature of concrete urban area devoid of green belt is higher by almost 4°C -6 °C compared to a thickly vegetated area. Further, significantly lower air temperature inside parks as well as in a transition zone outside the parks as compared to the surrounding built areas has been found.
Trees contribute to direct shading and evapo-transpirational cooling. An increase of tree canopy cover by 10% can reduce the surface temperatures on average by 1.4 to 2°C. It is important that planting schemes with trees should be such so as to reduce overheating but maintain good ventilation for better cooling effect.
Roof spaces, often underutilized, present a unique opportunity for the development of rooftop gardens. These gardens not only reclaim lost space but also offer thermal benefits to buildings, reducing both surface and air temperatures.
The vegetation on green roofs ranging from shrubs and trees to lawns can significantly lower the surface temperature compared to barren roofs. Green walls, too, have a cooling effect, breaking vertical air flow and reducing both air and surface temperatures by 2-6°C. The impact of green infrastructure on air quality is equally noteworthy.
Green roofs can combat air pollution particularly nitrogen dioxide, particulate matter and sulfur dioxide. Moreover, the cooling effect of green infrastructure can lead to substantial energy savings. The temperature reduction achieved by green walls and roofs can result in energy savings for cooling buildings ranging from 30% to 100%. Cool roofs, which can be 4° to 10°C cooler than conventional roofs, further contribute to energy efficiency and greenhouse gas emission reductions. Such urban green spaces provide calm and comforting environment for recreational activities.
Green urban spaces for recreational activities
Evergreen trees with dense foliage provide shade through out the year. Specially, during hot summer, ever green trees serve as cool and shady resting place during hot sunny days in summer. Example of such trees are Albizzia lebbeck, Alstonia scholaris, Azadirachta indica, Ficus spp, Peltophorum pterocarpus, Eugenia operculata, Eugenia jambolana, Mangifera indica, Samanea saman, Mimusops elengi, Polyalthia longifolia, Grevillea robusta, Thespesia populnea, Pongamia glabra. Bauhinia purpurea, Ixora parviflora, Calophyllum inophyllum, Parkia roxburghii, Kigellia pinnata, Saraca indica, Sterculia alata, Pterospermum acerifolium, Grewia columnaris, Tamarindus indica, Filicium decipiens, Putranjiva roxburghii, Santalum album, Swietenia mahagoni, etc.
Improved indoor air quality
A variety of foliage plants with ornamental foliage can be grown indoors. Foliage plants are those plants with attractive foliage and/or flowers that are produced in containers in shaded greenhouses or other structures. Foliage plants are valued for their foliar variegation in different combinations of colors and patterns, overall plant forms and styles. Most of them have a capacity to tolerate shade or thrive under indoor conditions. Urban flat dwellers can use such plants in various forms like container gardening, window-box gardening, gardening in hanging containers, roof gardening, etc. They not only add beauty and biological comfort but also improve the aesthetic outlook.
Indoor plant designs
Indoor plants can purify and revitalize air in our homes and offices, protecting us from the negative effects of such common toxins as ammonia, formaldehyde and benzene. Plants remove VOCs (Volatile Organic Compounds) from indoor air through stomatal uptake, absorption, and adsorption to plant surfaces. Several indoor species have been screened for their ability to remove benzene, in addition to other VOCs (e.g., toluene, TCE, m-xylene, hexane). The efficiency of VOC removal varies substantially among species and with the molecular characteristics of each compound. Research has also revealed significant decrease in the levels of CO2 and CO in indoor environment under AC as well as non AC conditions with the placement of potted indoor plants.
Plants like Aglaonema brevispathum, Pachira aquatic and Ficus benjamina reduced the levels of VOC’s like methane, toluene, ethyl benzene and formaldehyde. Many indoor plants species viz., Asplenium nidus, Ficus elastica, Hedera helix, Nephrolepis obliterata, Sinningia speciosa, Ocimum basilicum, Yucca massengena, Spathiphyllum wallisi, Diffenbachia spp., Rhapis excelsa can effectively reduce the VOCs (viz., HCHO, Toluene, Xylene, Acetaldehyde etc.) and CO2 from indoor air and increase aesthetic value. Further plants like succulents like Sansevieria, ZZ, Crassula, Haworthia, etc having CAM metabolism are highly beneficial for improving indoor air quality with the added benefit of requiring less water. Thus, plants in the home or office can filter out toxins, stale air, pollutants, harmful viruses and mould spores. Plants act as filters because they absorb the toxins through their leaves, especially those with the largest leaves.
Trends in urban greening
The scope of urban greening is quite broad, covering activities such as developing gardens in urban pockets, roof top gardens, vertical gardens or bio walls, interior scaping with plants, and kitchen and home gardening. It also includes the development of public parks, which serve as green lungs for cities, improving air quality and providing recreational spaces for residents. Besides, different modes of urban landscaping like xeriscaping, water-scaping, butterfly gardening, miniature gardening, rock garden, secluded garden, container gardening, window gardening, bonsai, etc are trends for urban beautification. Besides community gardens, fragrant gardens, moonlight gardens, herbal gardens, are the concepts being introduced. Theme gardens based on astronomy viz., Nakshatra van, sensory garden, is also becoming popular from education point of view. In indoor gardening, concept of terrariums, dishgarden, kokedama, etc
Conclusion
Urban greening in the urban vicinity can make a substantial contribution to enhancing environmental quality, augmenting health and happiness and elevating the bio-aesthetic appeal of our urban spaces. The integration of green spaces into urban landscapes emerges not just as a beneficial strategy, but as a critical imperative for environmental and public health. Urban greening, encompassing rooftop gardens, green walls, and expansive parks, plays a pivotal role in mitigating the adverse effects of urbanization. These green spaces are instrumental in reducing air and noise pollution, combating the urban heat island effect, and enhancing air quality. Moreover, they serve as vital lungs for cities, contributing to carbon sequestration and fostering biodiversity.
The therapeutic benefits extend beyond the physical, offering psychological restoration and stress alleviation, crucial in the fast-paced urban milieu. As cities continue to expand, the necessity for these green oases becomes increasingly paramount, not only for ecological balance but also for the well-being of urban dwellers. Beyond individual benefits, urban green spaces are integral to nurturing community cohesion and safety. They provide a communal ground for interaction, recreation, and engagement, strengthening social bonds and contributing to lower crime rates. For children, these spaces are indispensable for physical and cognitive development, fostering a connection with nature and encouraging healthier lifestyles.
The challenges of urban greening, such as space constraints and water scarcity, call for innovative solutions like vertical farming and rainwater harvesting. As we look towards the future, the role of urban green spaces transcends mere aesthetics; it becomes a cornerstone for sustainable, healthy, and resilient urban living. Embracing these green solutions is not just a choice but a necessity to ensure the prosperity and health of our urban ecosystems and their inhabitants.
