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Can living green walls help alleviate the impacts of climate change?

Earlier this year, the United Nations Intergovernmental Panel on Climate Change (IPCC) released their starkest report on the impacts of climate change, depicting the threats to both civilisations and ecosystems around the world.

The report documented that the effects of climate change have already impacted human health, livelihoods, and key infrastructure, particularly in urban settings. Hot extremes including heatwaves have intensified in cities, where they have also aggravated air pollution events and limited the functionality of urban infrastructure systems and services.

Essential infrastructure, such as transportation, water, sanitation, and energy systems have been compromised by both, extreme and slow-onset climatic events, resulting in economic losses, disruptions of services and impacts on human well-being.

Through an egalitarian lens, the report observed that these impacts are concentrated amongst the economically and socially marginalized urban residents. Climate change is effectively exacerbating existing social, economic, and environmental drivers of risk, especially for vulnerable groups who already lack access to essential services.

The authors of the report, urgently recommend an appropriate, widespread coordinated effort to adapt our urban environments to more extreme climatic conditions.

They believe that by improving existing and new infrastructure projects, our built environment can become more resilient to climate risks in the long term.

One way of achieving urban resilience is by providing greater access to ‘green infrastructure within our cityscapes. Green infrastructure refers to all types of vegetation that provides environmental, economic, and social benefits such as clean air and water, climate regulation and places for recreation.

An example of green infrastructure that can directly limit the effects of climate change within our urban environment is green walls, also termed living walls or vertical gardens. Green walls can form an important part of a wider strategy to increase the sustainability of our built environments by regulating temperatures and improving air quality.

Regulating temperatures

According to Dr Irga, from the University of Technology in Sydney, Australia

‘thermoregulation is one of the most researched benefits of green walls.’

He explained that ‘green walls can reduce high temperatures within buildings by intercepting solar radiation and through evaporative cooling.’

Conversely, temperature regulation is not just limited to heat reduction, as the insulation ability of green walls can also be of benefit in cold climates too. Through controlling temperatures, green walls enable buildings to be less reliant upon heaters and air conditioners, resulting in reductions in energy consumption.

Improving air quality

The natural, biological processes of green walls can improve air quality in the home and in urban settings by removing polluting air particulars.

The plants used within the green walls can capture airborne particles on their foliage and, with the associated microbial community, degrade a range of gaseous pollutants, including volatile organic compounds (VOCs).

VOCs are generated by motor vehicles, fires, industrial processes, and consumer products like paint. Some are highly toxic and prolonged exposure may increase the risk of health problems.

Aside from absorbing VOCs, green walls are also able to absorb carbon dioxide (CO2). All plants including those grown inside, or on the side of buildings, act as natural carbon dioxide filters. They absorb CO2 from the air to fuel the photosynthesis which allows them to grow and thrive. Presently, more research is needed to determine the most effective CO2 absorbing plants for vertical gardens.

Citygreen’s™ Living Wall system

Citygreen’s™ Living Wall system is a leading green wall product that can directly alleviate some of the risks created associated with climate change, by creating greener, cooler, and more liveable cities.

Citygreen’s™ Living Wall system embodies nearly

15 years of research, development, and product testing.

The design is available in nine standard panel sizes; however, it can also be engineered to retrofit walls on unique buildings.

The system is designed for quick and efficient installation for large scale commercial projects or smaller residential projects, with minimum disruption. The Living Wall system has irrigation lines embedded in a moisture retention layer to ensure optimal water distribution and water efficiency.

This enables both rapid and healthy plant growth post-install.

The assembly of the Citygreen’s™ Living Wall system incorporates a waterproofing layer, a moisture retention layer, and a breathable fabric layer with pockets for the soil so that a wide variety of plants can be selected and grown within the system.


The ability to adapt our urban centres to the unfolding risks of climate change is becoming ever more urgent.

Urban populations, particularly those in marginalised areas, are exceedingly feeling the impacts of more intense weather patterns.

Citygreen’s™ Living Wall system is a product that once installed, can rapidly start to alleviate some of the impacts of climate change, by regulating ambient temperatures, improving air quality conditions, and absorbing CO2.

P.J. Irga, et al, The distribution of green walls and green roofs throughout Australia: Do policy instruments influence the frequency of projects? Urban Forestry & Urban Greening, 24, 2017, 164-174.

Why modern day living needs more biophilic designs

As leaders in urban landscape solutions, the concept of biophilic design has been pioneered by Citygreen for almost two decades. Our mantra of transforming grey spaces into green, by incorporating nature into cityscapes, goes to the heart of what biophilic design is all about.

The term biophilia was first used by the pioneering naturalist and biologist Edward Wilson in 1984 when he hypothesised that humans have an “innate tendency to focus on life and lifelike processes.”

This tendency that Wilson speaks to, refers to the bond and deep sense of familiarity that humans and nature share. As a biologist, Wilson viewed life through an ecological lens, comparing lifelike processes to “organisms in an ecosystem.”

He believed that for societies to be functional, their surroundings must be akin to the natural environment that we were evolved in. In the man-made built environments, where most of the world’s population lives today, this sense of connection between nature and everyday human experiences has been slowly eroding.

During the COVID-19 global pandemic, lockdowns forced many of us to live in our neighbourhoods and home on a more permanent basis, which for a lot of people highlighted the lack of, and thus need for more innovative greenspaces.

Generally, the term greenspace invokes images of outdoor parks benches and beautifully manicured gardens, which is too simplistic in terms of 21st-century living. The standard approach in the past for town planners was to allocate a certain amount of open outdoor public space for conventional use, such as walking the dog or picnicking.

Yet today, with modern living requirements and conditions, the inter-relationship between greenspaces and greenspaces users has changed. As individuals, we are now spending more time inside buildings of all kinds, than we ever have before. Therefore, when we think of green spaces we should be contemplating indoor communal spaces like foyers in apartment buildings, food courts, and large shopping centres.

An example of a biophilic design that meets the needs of modern-day greenspace users is green walls, also termed living walls or vertical gardens. Such walls are becoming more popular, as they are able to convert underutilised areas into aesthetically appealing green spaces, by merging the natural and the built environments together.

Using straight walls and rights angles to recreate the scenic irregularities of the natural environment, has been a design goal for many sustainable companies including Citygreen. Green walls that incorporate a wide range of diverse plant species are able to artificially reinvent ecosystems, and can then bring the natural world closer to individuals, whether that be in a bustling inner-city workplace or residential apartment block.

Citygreen’s™ Living Wall system

Citygreen’s™ Living Wall system is a leading example of a modern biophilic design. Manufactured by the pioneering brand in advanced living wall products, Terapia Urbana in Spain, the Living Wall embodies nearly 15 years of research, development and product testing.

The system can be used outdoors, but indoor walls are by far the easiest, as the microclimate is more predictable, with the installation of artificial lighting, and automatic watering and fertilisation systems. Compared to other green spaces, the water usage for living walls like Citygreen’s™ Living Wall system is low, as it typically requires two litres per square metre per day to irrigate the wall.

The three features that make the system unique, and why it is able to stand out amongst other living wall designs, is firstly the fact that the wall, where the system will be mounted, will need no additional waterproofing. Secondly, the system is the lightest system on the market, weighing only 35kg per square meter fully planted and saturated.

Thirdly, the design is made up of a three-layer panel system that all links together, allowing the roots of the plants to be both protected, and have the ability to migrate freely, enabling almost unlimited root volume for the plants to grow in.

The design is available in nine standard panel sizes; however, it can also be engineered to fit bespoke sizes for unique projects. The system is also designed for quick and efficient installation for large scale commercial projects or smaller residential projects, with minimum disruption.

With urbanisation and residential density increasing in our modern-day societies, it is imperative that more cities and buildings be designed and planned in a sustainable way that allows individuals and communities to have equitable exposure to the natural environment.

Citygreen’s™ Living Wall system showcases a leading example of a creative and flexible design that can be used within challenging and ever-evolving modern-day greenspaces.

Learn more – Book Your Free Online Workshop

References: Edward O. Wilson. Biophilia. Harvard University Press. Cambridge, MA, and London, 1984.

Why don’t trees grow well in cities?

In every city, around the world, you see trees that are not meeting their full potential within the urban environment. To the human eye, these trees can appear twisted or have damaged branches, making them unhealthy and deformed.

In serve cases, the trees will gradually decline and end up being removed, with just an open space in the pavement remaining.

Sadly, cutting down dying trees from city landscapes has become all too familiar, and is something we want to explore in this article.

Designing a Tree Planting Method

One of the first reasons for unsuccessful tree growth, in many cases, lies in the failure to fully design a tree planting method. The implementation of any successful method, must first ask questions surrounding the location of the site: what is the soil profile that the tree is being planted into; will there be enough air-filled porosity or oxygen at the depth of planting; does the location have the necessary space to provide for the tree’s root system?

These questions must then be answered by adopting appropriate solutions, such as: applying nutrients to amend the soil profile where necessary; choosing the best-sized tree to fit the location, avoiding having to repair tree root damage to pavements; utilising road-based material that is conducive to tree growth; installing adequate draining mechanisms, so that the tree does not become waterlogged in wet seasons.

Typically, the cities with a healthy and thriving urban forest today, have adopted a comprehensively designed tree planting method to overcome the problem of frequent tree deaths within city landscapes. However, if a tree planting method, like the one discussed above, cannot be fully funded, then tree growing failures in cities will continue to occur.

Tree Planting Budget

To allow trees to reach full maturity, and ideally become self-sufficient, a suitable budget must be allocated. Without a sufficient budget, cities will experience the premature deaths of trees, which will need replacement within 3-5 years of planting.

A well-funded tree planting program would avoid the cost of continual tree removal and replacements, and alternatively appreciate the future value of trees as an asset within any urban environment.

Human Behaviors

Another reason for trees not growing well in cities is human behavior.

This can be broken up into a number of areas, but one is vandalism. Unfortunately, it is not uncommon, to see trees vandalized, especially young trees. Once trees are beyond a certain stage of life, they tend to be less susceptible to vandalism, but while they’re young, they are very vulnerable to being damaged by vandals: debarking trunks; snapping branches; or scratching graffiti onto limbs

Traffic impact is another human behavior that negatively affects tree growth. This frequently occurs with curb plantings, whereby trees are planted close to the roadside. If crown lifting is not performed, and the trees develop a low canopy, then low-lying branches can be smashed and damaged by passing traffic. This is especially the case, where you see a camber on the road that causes tall vehicles to intersect with the tree’s canopy, causing limbs and branches to tear off, allowing infection to set in.

Low-speed vehicular impact in parking lots can similarly impact tree growth. This frequently happens in parking lots, where trees have been planted with the best intentions, but wheel stops have been either omitted or placed in the wrong positions.

For example, at home improvement centers, frequented by trade vehicles with overhanging tray bodies; reverse parking can lead to vehicles, unintentionally smashing into the young trees.  This can be overcome by studying the trees surrounding, to allow for better tree placement and tree protection.

An Altered Environment

The urban climate in which trees are planted can also lead to poor growth performance. Cities have their own microclimate, which is a very different environment to the natural forest. It is well documented that some tree species will actually grow a lot faster in a city than they will in their natural open forest environment, because of the urban heat island effect, leading to warmer temperatures and thus more growth.

However, in a lot of cases, the urban environment does not necessarily result in successful tree growth.  For example, wind velocities in city landscapes are very different to the natural forest environment.

In the forest, trees are protected by one another against environmental forces of nature, but in urban planting, trees are typically planted on their own, and therefore become more exposed.

Adding to this exposure is the fact that the trees are often planted in close proximity to tall buildings, where the street forms a canyon. Winds can then blast up this ‘canyon’ with extremely high velocity, blowing the trees around, causing damage to the root systems.

Oftentimes, the wind will cause a young tree’s root system to be weakened, which may only be noticeable when the tree becomes much larger, unfortunately resulting in limbs breakages, or a whole tree collapses, which can be catastrophic.


Fortunately, there are solutions to all of these issues. Citygreen has decades of experience in successfully establishing urban forests to prevent premature tree death. A system that Citygreen has patented and used throughout the world with success is the Stratavault™ system.


Case Studies – Stratavault™ system

Downtown Ennis, located south of Dallas, in the United States, is known for its 19th-century historic architecture and iconic brick streets. With its current population of over 20,000, the city was looking to cultivate residential growth.

With this goal in mind, Citygreen’s Stratavault™ system was chosen the make the area more attractive, accessible and beneficial to downtown residents and tourists alike.

Adopting a ‘Green Streets’ approach, the areas impermeable curb and gutter section was replaced with a suspended paving system – that is, Citygreen’s Stratavault™ system, to allow trees to grow and thrive into maturity.

Capable of supporting heavy duty vehicular loading, permeable pavers were installed on top of soil cells which provided a medium for trees to grow in, whilst also capturing stormwater on-site to irrigate the trees.

Citygreen’s Stratavault™ was also utilised to enhance the redevelopment of Barangaroo South, in Sydney, Australia.

Designed to encourage both passive and active outdoor activities, the redevelopment of Barangaroo South’s landscape, initially faced significant difficulties. The density of paved areas and streets, was not able to provide a conducive environment for trees to thrive in.

To overcome this problem, Citygreen’s Stratavault™ was utilised. With its open matrix design, the system ensures that there is enough uncompacted soil space to facilitate strong root growth without damaging the surrounding paved surfaces.

Call us Today

As shown above, Citygreen is an expert in every phase of design, and implementation of streetscape upgrades, incorporating healthy, sustainable green infrastructure – reach out to Citygreen for a Design Workshop today.

How much soil do street trees need?

This question often comes up, in workshops about the urban forest.

Tree Root systems are extensive

The first thing to understand is that the root system of a tree is far more extensive than many people realize. In a natural environment, the root system extends as deep as possible in the soil profile, and typically very, very broadly in the upper layer of the soil profile. Wherever there is sufficient oxygen in the soil, and friability in the soil, to support the root growth of the tree – the roots will explore.

The root plate supports the canopy – but you can’t see it

The root system of the tree provides the structural support for the above-ground canopy, which is the part that we all see. That is a very, very critical function. A tree’s canopy can be very large, is extremely heavy, and is acted upon by the forces of nature – like wind, snow, rainfall etc. Within cities, the power of wind, (sometimes known as wind tunnel effect, or canyon effect), caused by proximity to tall buildings, causes ‘wind-throw’ forces in cities to be much greater than in a forest. So a tree’s root system is critical to anchor the tree physically, and also to support the healthy growth of the above-ground canopy.

A bigger tree requires a bigger soil volume

It’s important that we understand that the amount of soil required is relative to the mature canopy size of the chosen tree species. It’s not related to the size, pot, or box that the tree was grown in at the nursery. The quantity of soil volume that you provide for a tree in the street is all the soil that that tree is going to get – for its entire life. It’s important that the right amount is provided.

What is a tree coffin?

Historically, trees have been planted in small openings in pavements, sometimes called tree coffins. But this has resulted in catastrophic failure in pavements, and surrounding infrastructure, premature mortality for the tree, or consigning a tree to being stunted for its life if it does live. Walk the streets of any city in the world, and you will see this.  So, it’s critical that the concept of soil volume is understood, if we truly wish to grow a healthy urban forest for future generations. The surprising fact is that with the correct volumes of good quality soil – the benefits can be enjoyed within your generation. The growth rates are astounding – we just need to get the basics right.

The Treepit area is really important

Tree roots will grow a long way out from the trunk. Many people have had the experience of having an underground sewer or storm pipe penetrated by a tree’s root system, and the tree was growing a long way away, in a neighbor’s property. Trees will grow a long way out from the trunk – in many cases well beyond the canopy area.

‘Deep Soil Zones’            

The other thing to be understood is the fact that depth of soil is also vital to accommodate the sheer size of the tree root system. For this reason, many cities are now mandating ‘deep soil zones’ for tree planting. This is critical, and is a very good move, to ensure that there is quality soil at a suitable depth, for the life needs of the urban forest As said before, tree root systems will grow as deep as there is adequate moisture, adequate aeration, (oxygen), as well as the essential elements of healthy soil.

So, how to calculate the volume required?

To arrive at a soil volume for a street tree, one simple rule of thumb is to start with the mature canopy size of the tree. Look up reliable tree resources, investigate online, or speak to the tree nursery, and establish what the mature canopy diameter of the tree species is going to be. Generally, this is very readily available. To what width will that tree grow at its full capacity? Then you turn the diameter into the area, by using the area formula. That gives you the area of the mature canopy (shade). Then you take that area, and multiply it by 0.6x a meter, or two feet in depth, to arrive at a target soil volume. Now, this is a rule of thumb, but it’s a very good place to start. There are other, more complicated formulas – but this is a good place to start.

Finding space for deep soil zones

Rarely is there room in a sidewalk, or a parking lot, or a paved area, for the entire deep soil zone to be an open garden bed. Due to pedestrian access demands, and vehicular movements – there is a requirement for extensive use of hard pavements.  The good news is, there are ways of supporting the pavement while maintaining deep soil zones beneath that pavement. But establishing a correct soil volume for street trees is the first step in establishing a healthy and sustainable urban forest, and there are several ways of arriving at target costing based upon this.

To learn more about how to design and implement a successful urban forest project, engage with an expert here.

What are the positive effects of Biophilic Urban Planning?

Biophilic design has been gaining interest within the construction and urban planning industries. Trying to incorporate nature into buildings and public spaces intends to promote people’s health and wellbeing, as well as create spaces with sustainability built-in.

In recent years, numerous researchers have discovered solid connections between more time spent in nature and better physical and mental health.

Nature’s effectiveness for mental health is especially promising, as mental health problems account for as many as one in three cumulative years that people live with a disability. The toll of mental health issues on the population as a whole is similar to that of cardiovascular disease and circulatory disorders.

The biophilic design offers to help people get more exposure to nature by bringing nature into cities, buildings, and public spaces.

Some environmental engineers, such as Princeton University’s Anu Ramaswami in an interview with New Scientist recently, argue that green public spaces are just as important parts of city management and urban planning as shelter, water, food, energy, connectivity, and sanitation. People in cities all need these things to live healthily.

What is Biophilic Design?

The biophilic design borrows concepts from biologist Edward O. Wilson. Wilson posited the “biophilia” hypothesis in 1984. He believed that our brains have been shaped by the environment we evolved in, primed by it to respond well to cues that would help us with survival.

Natural objects like trees, savannahs, lakes, and waterways help to mark locations that would provide our basic needs such as food, water, and shelter. In the first 294,000 years of our existence as a species, we always lived outside of cities.

When we eventually started building cities around 6,000 years ago, our brains still craved seeing and being near these natural markers of survivability in the environment. In fact, as a species, we have only become predominantly urban dwellers in the last few decades. But, by 2050, this will likely increase to around 70% of the world’s population living in cities.

The biophilic design tries to tie these two phenomena together: biophilia causing our brains to favour natural environments, and increased urbanization taking more of us outside of natural environments and into man-made environments.

The biophilic design focuses on including natural objects like trees, waterways, and plants in public spaces. Natural shapes like curves, irregular arcs, and shapes that mottle light are also used in exteriors and interiors of biophilic buildings to appeal to us.

This is supported by recent science. In a 2019 study led by the University of Exeter, UK, researchers found that between 120 and 200 minutes of recreational contact with nature each week was associated with good health or wellbeing. The study involved almost 20,000 participants from around England.

However, biophilic designs and time in nature may not be helpful for everybody. It is important to note that the majority of research into nature’s effects on wellbeing has been conducted in Western societies. Mental health benefits from accessing nature are probably influenced by a number of factors that include age, gender, personality, socioeconomic status, and culture.

Examples of Biophilic Design in Urban Planning and Construction

Some buildings, such as One Central Park in Sydney, Pasona Group Offices in Tokyo, and Bosco Verticale in Milan, feature biophilic design by incorporating plants and trees into their exteriors, interiors, and built environment on ground level.

Urban areas have for many years been subject to beautification schemes including bringing nature back into the urban environment. An early example in the UK is the Garden City movement in the early 1900s, but the recent announcement that France is going to heavily reduce traffic on the Champs-Elysées and turn it green continues this tradition into the present day.

The Million Trees Los Angeles initiative and the wide-scale greening program in New York City are good examples of how municipal governments in the United States are responding to the benefits of biophilic design.

Further Benefits of Biophilic Urban Planning

Biophilic urban planning has myriad benefits for citizens and the wider environment as well.

There is a wealth of evidence for the positive effects of nature on psychological conditions like depression, anxiety disorders, and mood disorders. Sleep, stress, happiness, emotions, social interactions, and even a sense of meaning in life can all be impacted positively by spending time in nature. Attention, memory, and creativity are also boosted by time spent in nature.

Physical health is improved when plants and vegetation in cities work to absorb airborne particulates and other pollutants from exhaust engines and heavy industry.

Natural space in cities also helps to improve cities’ sustainability. It provides free environmental benefits like clean air and water, flood defence, and natural shade. On buildings, vegetation can help to regulate temperature and air quality and reduce the building’s climate footprint.


Source: Written by Ben Pilkington published on

GREEN AND GREY: The use of nature-based solution to tackle urban challenges

1. Urban challenges: why we need nature-based solutions

In the present day and age, we tend to think about cities and nature as two incompatible opposites: on one side, the grey, sterile, polluted city, overcrowded with people and cars; on the other side, the green, fertile nature, filled with life. Recently, however, more and more researchers, urban planners and citizens have started talking about living infrastructure, biophilic urbanism and rewilding: all these terms refer to the use of natural elements in the cities to deliver ecosystem services benefitting both man and biodiversity. In fact, over the years it has become clear that the current urban planning models and the sole use of architectural and engineering solutions are not enough to tackle the challenges of living in cities. Air and noise pollution, floods, the heat-island effect, a general lack of beauty and green spaces, respiratory diseases, obesity, depression, are all phenomena we have come to accept as a natural consequence of living in cities. Shouldn’t things be different?

As the IUCN defines them, nature-based solutions are “actions to protect, sustainably manage and restore natural and modified ecosystems in ways that address societal challenges effectively and adaptively, to provide both human well-being and biodiversity benefits.” I would like to name a few of these solutions and show how their implementation would benefit urban areas.

2. Green walls and green roofs

Both green walls and green roofs are green infrastructures combining architectural elements and vegetation.

Green walls, or vertical gardens, are structures installed on an indoor or outdoor wall consisting of a growth medium such as soil or hydroculture felt, a hydration and fertigation delivery system and a layer of selected vegetation, chosen primarily based on the local conditions of humidity and sun exposure. Green walls deliver several benefits:

  • Aesthetic improvement: it is the first reason for their installation. Indoor vertical gardens could be seen in several luxury buildings and shops across all the major cities of the world and have become a trend in interior design. They are also installed outdoors, but, given the not so cheap costs of realisation, they are less common. A wonderful example of an outdoor green wall is the Musée du Quai Branly, in Paris. If the technology were cheaper, it could be installed on more buildings to guarantee a better equilibrium between concrete and vegetation.
  • Pollutant reduction: it is well known that the presence of vegetation helps to reduce the concentration of particulate matter in the atmosphere by dispersing the particles that collide with the leaves and by trapping them in the waxy and hairy leaf surface (when it rains, the particles are then washed away into drains and consequently into water-treatment plants). Several studies are now concentrating on the quantification of pollutant reduction and on the selection of the most suitable plant species. Green walls could therefore help to reduce particulate concentration in those densely populated areas the space for public green is limited, thus providing a sanitary benefit to the citizens.
  • Noise reduction: vegetation acts as a noise insulator and for this reason improves the inhabitants’ life quality.
  • Thermal insulation: vegetation would provide better energy efficiency for the buildings.
  • Heat island effect reduction: evapotranspiration reduces heat emanating from asphalt and concrete, improving the citizens’ life quality in summer, and reducing the need for air conditioning.
  • Ecological benefits: green walls could potentially have positive ecological impacts, such as the attraction of birds and insects, but further research is needed.

Green roofs are roofs covered with vegetation, a growing medium and a waterproofing membrane. Two typologies exist intensive roofs, which are thicker and can support heavier plants and trees, but require more maintenance; extensive roofs, meaning they are shallower and require less maintenance, and are usually planted with vegetation resistant both to humidity and to a lack of water, such as Sedum. Some of the benefits they provide are like those of green walls, while others are exclusive to green roofs:

  • Noise reduction, heat-island effect reduction, thermal insulation.
  • Use of unused surfaces: in the cities, where the room for private gardens is limited, the installation of green roofs comes with the possibility to use that new surface in the free time. In addition, they contribute to reducing the consumption of soil, a non-renewable resource.
  • Water retention: the vegetation and the absorbing layers retain the water and return it back to the drain later after the rain event. This helps the water-treatment plants to face high-intensity rain events without going over-capacity and to reduce the pressure on sewage. In addition, it could be possible to use the collected water for sanitary ware, given that nowadays in Italy we still use perfectly drinkable water for that purpose.
  • Ecological benefits: evidence shows that green roofs host a greater species diversity than conventional roofs, but it is still unclear whether they could be ecologically relevant in the context of the urban landscape, thus more studies are necessary.

3. Rain gardens

Rain gardens are a typology of sustainable urban drainage systems, which combine both engineering and natural elements to manage water in urban and peri-urban areas. The base concept underpinning SUDs is the sponge city: born in China, this model aims at the absorption of water during storm events and the later restitution in drains. This may seem obvious, but the more frequent flooding events have made clear that the stress put on drains, sewages and water plants exceeds their management capacity. With the expansion of cities and the increasing soil impermeabilization, this problem will only get worse. SUDs involve permeable surfaces in parking lots, green roofs, bioswales, wetlands, retention basins, rain gardens. However, despite their potential, they still are not commonly employed, also due to the lack of long-term studies on their effectiveness.

Rain gardens are conceptually very simple: they are gardens planted in a slight depression, often with a drainage pipe connected to the sewers. Thanks to the lower infiltration rate of the soil and to the plants, they retain the water for 24-48 hours thus reducing the stress on the water treatment facility. They also provide many more benefits:

  • Low costs of installation and management.
  • Water depuration from metals and organic pollutants thanks to the bioremediation mediated by bacteria in the soil or in the zeolite or gravel beds.
  • Heat-island effect reduction.
  • Aesthetic improvement of the city: in fact, they are virtually indistinguishable from common gardens.
  • Creation of habitats for pollinators.

4. Final considerations

Nature-based solutions are a very fascinating concept, and their strength lies in their low costs of maintenance and in the provision of several benefits: considering the growing pressure that cities will bear soon, there is a lot of room for their use. Urban planners and governors should implement and incentivise these solutions, while researchers should focus on the quantification of the benefits they provide and on the improvement of their efficacy.

Several cities in Italy are densely populated and suffer from a lot of the abovementioned problems, some of which are getting worse because of climate change. Unless we want to be left behind by Europe, China, and the rest of the world, now is the time to invest and experiment with nature-based solutions and green infrastructures.


Source: Written by Laura Besana, MSc student in Environmental Sciences and Technologies as published on Linkedin

Study claims ‘Living walls’ of plants can cut your energy bill by reducing heat loss by 30%

  • ‘Living walls’ of plants can reduce heat loss by 30% 
  • University of Plymouth researchers measured two walls of a pre-1970s building
  • One of them was retrofitted with an exterior living wall façade for soil and planting
  • Five weeks of measurements showed that less heat was lost through the living wall

A new study found that the ‘living walls’ of plants can slash your energy bill by reducing the amount of heating lost through its structure by more than 30%. The research, carried out by the University of Plymouth, used the Sustainability Hub – a pre-1970s building on the university campus – to measure how effectively two sections of its walls retained heat.

One of them was retrofitted with an exterior living wall façade, made up of a fabric sheet system with pockets allowing for soil and planting. After five weeks of measurements, researchers found the amount of heat lost through the living wall was 31.4 per cent lower than that of the original structure. They also discovered daytime temperatures within the newly-covered section remained more stable than the area with exposed masonry, meaning less energy was required to heat it.

Dr Matthew Fox, a researcher in sustainable architecture and the study’s lead author, said:

‘Within England, approximately 57% of all buildings were built before 1964. While regulations have changed more recently to improve the thermal performance of new constructions, it is our existing buildings that require the most energy to heat and are a significant contributor to carbon emissions. It is therefore essential that we begin to improve the thermal performance of these existing buildings if the UK is to reach its target of net-zero carbon emission by 2050, and help to reduce the likelihood of fuel poverty from rising energy prices.’

The study is one of the first to ascertain the thermal influence of living wall systems on existing buildings and was carried out by academics associated with the university’s Sustainable Earth Institute. Researchers said that while the concept is relatively new, it has already been shown to bring a host of benefits such as added biodiversity.

With buildings accounting for 17% of greenhouse gas emissions – and space heating accounts for over 60% of all energy used in buildings – the authors believe their findings could be a game-changer in helping achieve its net-zero commitments by 2050.

Dr Thomas Murphy, one of the researchers, said:

‘With an expanding urban population, “green infrastructure” is a potential nature-based solution which provides an opportunity to tackle climate change, air pollution and biodiversity loss, whilst facilitating low carbon economic growth. ‘Living walls can offer improved air quality, noise reduction and elevated health and wellbeing. ‘Our research suggests living walls can also provide significant energy savings to help reduce the carbon footprint of existing buildings. ‘Further optimising these living wall systems, however, is now needed to help maximise the environmental benefits and reduce some of the sustainability costs.’

The study has been published in the journal Building and Environment.


How Europe’s Greenest Capital Is Saving City Trees

“Covered either by bristling forests or by foul swamps” is how Tacitus described the wildlands of Germania in 98 AD. While those ancient trees, from which Teutonic tribes emerged to maraud the Romans, have long since vanished, modern Germany’s capital is still home to a vast and vital urban forest.

Berlin is one of the greenest cities in Europe: About a third is taken up by parks and green spaces, and the streets are lined by more than 430,000 street trees. Lindens (also known as lime trees or basswoods) are the most common, their heart-shaped leaves visible all over the city. They even lend their name to the grand central boulevard, Unter den Linden, once Berlin’s answer to the Champs Elysée or 5th Avenue.

Street lindens belong to the cityscape as much as the palms of LA or the sakura of Tokyo, though few of Berlin’s thousands of streets trees are older than 70. During the 1940s, 60%of street trees were wiped out by the onslaught of the Second World War. Trees that survived the Allied bombing were cut down for firewood in the freezing winters that followed.

(Photo by Marco Derksen / CC BY-NC 2.0)

Post-war, reforesting the ruins became an act of restoration and resilience. The first linden was replanted in the Tiergarten in 1949 by Mayor Ernst Reuter, during the Soviet blockade of West Berlin. The replanting effort was judged to be so important for morale that, along with essential food and fuel supplies, up to 200,000 young saplings were flown into the divided city by the U.S. Air Force.

Now, Berlin’s recovered tree population is once again at risk — this time from a chronic drought — and a new app has been launched to save them.

Gieß den Kiez (Water the Neighborhood) is an interactive platform that invites users to keep an eye on local trees and in times of need, bring them a bucket of water or splash from a hose. The map displays over 600,000 individual trees (both street trees and park trees), together with up-to-date information on species, age, water needs, and recent rainfall.

The prototype was developed at CityLAB Berlin, a research and development hub funded by the Berlin Senate and Technologiestiftung Berlin. Julia Zimmerman is part of the team. “We want to show people what kinds of digital solutions there are for real-life problems,” she explains. For most users, the map gives a completely new perspective of life on their street. “That was the first thing I did with the website,” Julia says. “Check which trees are growing outside my front door.”

But it’s not just a novelty. For the first time in generations, tree numbers in Berlin are falling. The principal cause is extreme weather. First came Cyclone Xavier in 2017, which uprooted and damaged thousands of trees across the city. Then came chronic droughts: Both 2018 and 2019 recorded high temperatures and minimal rainfall in spring and summer, and 2020 is shaping up to follow the same pattern.

“The situation is very urgent,” explains Christian Hönig from the environmental group BUND-Berlin. “In the last very dry years since 2018, the annual number of street trees felled has increased by about 20 %.” Street trees bring a host of benefits to the city. They regulate temperature, filter airborne pollutants, and provide a home to local wildlife. “They also shape the space we live in,” says Christian, “just like architecture.”

Urban tree care does not come cheap, however, and Berlin’s finances are famously dire. According to the Berlin Senate, it costs €2,000 (about $2,250 USD) to plant and maintain a tree in the first two years, during which time the young plantings can need as much as 50 litres (13 gallons) of water per day if temperatures are high.

Faced with dramatic tree losses, the city has already made €22 million (about $26 million USD) of extra funding available to district councils for 2020, and spending per street tree has been increased from €48 to €82 ($56 to $96). An annual campaign is also underway to raise donations from the public.

But as temperatures rise and skies above Berlin remain blue, street trees young and old need all the help they can get. This is where Gieß den Kiez, with its model of neighbourhoods watered by the neighbours, could bring about a radical change in how city trees are cared for.

Every tree in Berlin is mapped so users can see how much water a tree has received and how much it still needs. (Screenshot from Geiß den Kiez)

The prototype went live in May and in the first six weeks, registered 1,000 unique users and over 7,000 individual tree waterings. “The first weeks were totally crazy,” Julia laughs. “Through coronavirus, I think a lot of people found more time for themselves and also for their environment, for nature.”

User numbers are still rising daily and community groups are using the platform to coordinate their watering activities with local authorities. She is also pleased to see that elderly users are getting in touch with questions about using the platform. “The issue is encouraging older people to get to grips with new technology.”

“I find it really beautiful to see the issue is so important to the people of Berlin,” she adds. “I’m optimistic when I see how big the community is, how much the different district councils are reaching out to us. They all seem to have woken up.”

Open tree data

Open platforms like the Gieß den Kiez, which make public data accessible, can be a powerful way to get citizens engaged in city issues.

“It can help people to have a better appreciation of how it is the government does what it does, so there’s less of a wall between them and government, as this mysterious thing,” says Steve Benett. He is the founder of Open Trees, the world’s biggest database of open tree data. Using datasets from public sources, he has mapped street and park trees from cities around the world onto a single global map.

“It’s not that obvious to the average citizen just how many frickin trees there are,” he says. Visualisations like his can help people understand the challenge of caring for hundreds of thousands of trees in a major urban area. “You get this squeeze, where the government has to turn back to the citizens and say, well maybe we can’t water all the trees, maybe you’re going to have to come and help out.”

Sharing stewardship online

Cities in the U.S. have been experimenting with similar platforms, to win more volunteers in the fight to protect and care for urban forests.

The New York City Tree Map is run by the NYC Parks Department and shows data on 692,892 trees across the five boroughs, including a log of volunteer care activity, from watering to mulching, and a running tally of the annual value of urban trees to the city (currently $104,991,168.49, a reflection of trees’ roles as shade, carbon dioxide and pollution removers, and stormwater retainers).

“The map is intended to be the one-stop shop for New Yorkers to learn about and care for their street trees,” says Dan Kastanis from NYC Parks. Built from data gathered by an army of volunteers in the 2015 tree census, the map is designed to give a live connection to the status of each individual tree, as well as resources on tree care and community workshops. Though New York’s map is the most sophisticated, other cities like Washington, D.C., Seattle, San Francisco and Los Angeles have all published their tree data on similar platforms.

These projects all share the conviction that finding engaging ways to visualise and interact with data can inspire locals to get involved and become active volunteers. Tree stewardship is a model in which citizens and local government share the work of tree care, not just in seasonal crises like a drought but on a basis of long-term cooperation.

“We believe stewardship of our urban forests requires a team-based approach,” says Rachel Holmes from The Nature Conservancy. In collaboration with the U.S. Forest Service and the Center for Invasive Species and Ecosystem Health at the University of Georgia, she works on Healthy Trees, Healthy Cities, another tree care and mapping platform. “By first educating people about trees and what they need from us, and then providing an accessible mechanism through which people can meet these needs, we are hoping to inspire a lifelong connection to nature and commitment to its care.”

Sharing responsibility

Yet the burden of ownership which online stewardship seeks to foster is not always welcome. Some communities raise concerns about the maintenance costs of new trees. In San Francisco, for instance, homeowners, and not the city, bore legal responsibility for any damage caused by trees growing in the sidewalk adjoining their property — including eye-watering bills for root damage to sewers — until the law was changed in 2016.

Street trees also bear out the legacy of social and economic inequality. A 2016 study of the City of Los Angeles found the benefits offered by street trees was skewed, with nearly a fifth of the urban canopy growing in an area where only 1% of the population lives. At the same time, planting trees can seem tokenistic in the face of long-standing neglect. In Detroit, there was pushback against tree planting initiatives by communities who felt abandoned by city authorities in so many other ways that they felt no stake in the planting of trees. If city forests are to be recognised and protected as green infrastructure, with benefits available for all, then addressing inequality must also be part of that conversation.

For Julia Zimmerman, community apps like Gieß den Kiez can help us recognise trees as a point of connection in the shared life of a city, part of its past as well as its future.

“Berlin is and will hopefully stay a green city,” she says. Along with one of her favourite streets, Puschkinallee, towering plane trees have stood since the late 1870s, improbable survivors of history. Their loss would be shared by all Berliners. “Especially in a city like Berlin, where the past is extremely moving — and the trees have lived through all of it with us.”

Source: Written by Edward Belleville based in Berlin

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