Daniel Biek

Cities are associated with being grey, sterile, polluted and overcrowded with people and cars. However, over the years it has become clear that, not only architectural and engineering solutions are enough for urban planning. Modern cities ought to deliver ecosystems services benefitting both human and biodiversity. Should not be nature an essential part of ta city ?

The “International Union for Conversation of Nature” (IUCN) defines nature-based solutions are “actions to protect, sustainably manage, and restore natural and modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits.” (IUCN, 2020). In the following I would like to illustrate a few solutions and how urban areas can benefit from their implementation.

Green Walls and Roofs

Green roofs are “contained” green space on top of existing roofs. Important layers are the root and waterproofing barrier, which both prevents that the roof is affected and the plants with its growing medium. Depending on the thickness, even heavier plants or trees are plantable, but then there is more need for maintenance (About Green Roofs, 2022). Green walls, also called vertical garden, are on indoor or outdoor walls consisting of a growth medium such as soil or hydroculture felt, a hydration and fertigation delivery system and the vegetation (About Green Walls, 2022). Since the vegetation are acting like noise insulator, it can reduce the noise and therefore make inhabitant’s life better. Another major advantage is the reduction of the heat island effect. Because of evapotranspiration, the heat radiated from asphalt and concreted is reduced, which results in general cooling of the city. Additionally, green walls cool the wall behind them and through shading, they lower the temperature in the city. Due to the better thermal insulation, the management of the temperature in the building is less power consumed. These energy savings can potentially reduce the amount of greenhouse gases. Green roofs are one way to manage stormwater. Not only tthere is a decrease in the amount of runoff stormwater, but also the time at which runoff occurs isl delayed because of partly storage of the water by the substrate. As a result, there is less stress on sewer systems at peak flow periods. Furthermore, the plants can capture airborne pollutants, atmospheric deposition and filter even noxious gases. All these advantages can also lead to economic benefits: possible reduction of cooling/heating costs, saving energy costs and the lifespan of roofs can be extended (About Green Roofs, 2022; About Green Walls, 2022; Green Infrastructure: Green Roofs and Walls | Asla.Org, 2022)

Left: Green roofs in Singapore; Right: Green wall in London (‘Green Roofs in Singapore’, 2013) (‘City of London Green City Briefings – Green Roofs and Walls’, 2021)

Rain Gardens

Rain gardens are an area close to buildings, in which native shrubs, perennials and flowers are planted in a small depression. Therefore, they creates a natural slope and their location is stragetically. Thus, they capture rain and/or stormwater runoff. The principle is that the runoff is infiltrated into the soil and thus reabsorption is happening. (Groundwater: Rain Gardens, 2022; Rain Gardens, 2021). In contrast to ponds, the water in the rain garden is there only for a short time (a few days) and usually do not accumulate. Consequently, it is not a mosquito-breeding site. Additionally, they are not covered and not deeper than a foot, but the actual depth depends on how much water shall be collected. Another positive side effect, that rain gardens provide habitat and floral resources for pollinators. One crucial step is the planning. First, the diversity of plants is important, since they are part of an ecosystem for example being a butterfly host and need to tolerate occasional flooding or even drought in regions with less rain. One possible choice is deep rooted native plants due to their drought tolerance and the ability to drive back the water. Furthermore, the tolerance of soil moisture plays a major role. Generally, the lowest part of the garden is wet, and the edge (highest part) is usually drier. The area between them is the transition or medium area. Hence, the soil moisture is different within the garden and affects the plants. Differently to other types of gardens, rain gardens are usually planted more densely in order to slow the water movement. A further effect is that it allows the root to knit together, which results in holding the soil (Rain Gardens Are a Win/Win, 2018).

Example of a rain garden (Groundwater: Rain Gardens, 2022a)

Challenges

These two types of nature-based solutions are good examples for improving the city quality and make it greener. Apart from the mentioned advantages, it is stated that it also helps to improve the mental health and the life quality (About Green Roofs, 2022; About Green Walls, 2022; Rain Gardens Are a Win/Win, 2018). However, part of the evaluation of one solution is to also illustrate the possible disadvantages/challenges. Regarding green roofs and walls, the initial costs are higher and could prevent someone to invest into this solution. Moreover, due to green roofs the load on the building is higher and thus careful planning is necessary when implementing a green roof (General Services Administration, 2011). As all other plants, nature-based solutions need regular and proper maintenance, in particular green roofs and walls. Irregular or no maintenance can lead to structural damage, or the drainage system is clogged from leaves, seeds etc. (Woods, 2018). Another disadvantage is that during a drought, green roofs and walls put additional load on the strained water system due to their need for large amounts of water. In general, both are highly weather dependent and therefore, unexpected consequences can happen occasionally (General Services Administration, 2011). In case of rain gardens, the size might be too small to have strong effect. Thus, more gardens are needed in order to distress other systems while runoff of water (Rain Gardens, 2021). As indicated above, proper planning and landscape design are necessary to get the most out of these solutions.

Conclusion

Nature-based solutions and their strength lies in providing several benefits to various aspects: ecological, mental, environmental, and general life quality. Nevertheless, the challenges are undoubtedly present and there is aneed for new ideas/approaches in order to increase the number of nature-based solutions in cities. Generally, there is a lot of space to implement the described ideas and to my mind the advantages predominate the drawbacks. The implementation can make cities greener, more sustainable and improve their quality. Who doesn’t want to live in a city where “green” and “grey” coexist?

References

About Green Roofs. (2022, April 12). Green Roofs for Healthy Cities. https://greenroofs.org/about-green-roofs

About Green Walls. (2022, April 12). Green Roofs for Healthy Cities. https://greenroofs.org/about-green-walls

City of London Green City Briefings – Green Roofs and Walls. (2021, June 15). Greenroofs.Com. https://www.greenroofs.com/event/city-of-london-green-city-briefings-green-roofs-and-walls/

General Services Administration. (2011). Challenges to green roof construction. https://www.gsa.gov/cdnstatic/Challenges_to_Green_Roof_Construction.pdf

Green Infrastructure: Green Roofs and Walls | asla.org. (2022, April 12). https://www.asla.org/contentdetail.aspx?id=43536

Green Roofs in Singapore. (2013, December 23). Green Roof Technology. https://greenrooftechnology.com/green-roofs-in-singapore/

Groundwater: Rain Gardens. (2022, April 12). https://www.groundwater.org/action/home/raingardens.html

IUCN. (2020, January 31). IUCN. https://www.iucn.org/theme/nature-based-solutions

Rain gardens. (2021, December 9). https://www.susdrain.org/delivering-suds/using-suds/suds-components/infiltration/rain-gardens.html

Rain Gardens Are a Win/Win. (2018, April 4). Xerces Society. https://xerces.org/blog/rain-gardens-are-winwin

Woods, R. (2018, February 13). How Living Plant Walls are Damaging Buildings. https://www.evergreenwalls.com.au/blog/living-plant-walls-damaging-buildings