The Growing Need for Urban Gardens - A Look at the Positive Impacts for Climate Change Adaptation

As our cities continue to urbanize, the loss of valuable green space is inevitable. Beyond the positive benefits of social cohesion, community attachment, and physical exercise, urban gardens play a pivotal role in helping our cities battle climate change’s most direct consequences.

Flooding

In many parts of Ontario last year such as the City of Toronto, it was evident there is no place that is immune to the impacts of our warming climate. The city experienced a significant rainfall event, resulting in the flooding of roads, transit stations, and homes (Aziz, 2024).

There is much evidence on the impact of reducing impervious surfaces such as asphalt and concrete, opting for more permeable surfaces. That is, surfaces which absorb water faster, such as porous asphalt and concrete, gravel, and of course, grass.

The paving of front gardens to make way for off-street parking results in increased water run-off and reduced runoff times, overwhelming storm drainage systems, and increasing flood risks. A study which modelled the impacts of increasing impervious surfaces on water runoff volumes during a 1 in 50 rainfall event in the UK found that increasing impervious surfaces in front gardens by 10% resulted in a 9.7% water runoff volume. (D.A. Kelly, 2016).

Further, a study in Brussels, Belgium found that increasing rooftop gardens by 10% could result in a 54% reduction in stormwater runoff for the building and a 2.7% reduction in the region (Mentens et al., 2006).

Including more green spaces of all types such as community gardens, rain gardens, rooftop gardens, and preserving natural spaces wherever possible can play a huge role in combating flooding in our cities today.

Urban Heat Island Effect

There is no doubt that our cities are rapidly becoming warmer. The urban heat island effect is a phenomenon where our cities are heating up faster than rural areas due to buildings being packed closer together and paved surfaces which trap heat, resulting in a heat island effect.

It is also worth mentioning the albedo effect which plays a large part in making this happen. Darker, paved surfaces are unable to reflect heat into the atmosphere, rather they absorb it causing the ground to warm up quickly. Green spaces absorb much less heat and can provide a cooling effect as they release moisture. White spaces are the most effective as they reflect radiation back up into the atmosphere (Susca et al., 2011).

On a sunny, hot day, concrete can heat up to 27-50°C hotter than the air temperature (Climate Atlas of Canada, n.d.). In Arizona, burn beds in hospitals fill up every summer from people falling onto the pavement. There have been cases of patients with

third-degree burns caused in less than a few minutes of contact with the ground (Christensen, 2023). It’s an emerging issue in many cities experiencing extreme heat due to climate change and one that needs to be addressed quickly.

One way to tackle this is by increasing green spaces in our cities. Rooftop gardens, for example, can provide a cooling effect through evapotranspiration and reduce energy costs for buildings. A study on three roofs in Queens, New York found that in the period of 50 years, replacing one square meter of roof with green roof could mitigate 38 kg of CO2eq (Susca et al., 2011). Planting more trees can provide shade, cooling the pavement and making walking less burdensome during times of high heat.

Ultimately, the benefits of gardens in urban settlements are endless and integrating more of them may be key to mitigating the challenges posed by climate change, allowing us to build a sustainable and resilient future for our cities.

Sources

Aziz, S. (2024, July 17). Toronto flooding a ‘significant event,’ need to step up climate change fight: Trudeau. Global News.

https://globalnews.ca/news/10629154/toronto-flooding-trudeau-significant-event/

Climate Atlas of Canada. (n.d.). Urban Heat Island Effect. https://climateatlas.ca/urban-heat-island-effect

Christensen, J. (2023, July 24). It’s so hot in Arizona, doctors are treating a spike of patients who were burned by falling on the ground. CNN https://www.cnn.com/2023/07/24/health/arizona-heat-burns-er/index.html

Kelly, D. A. (2018). Impact of paved front gardens on current and future urban flooding.

Journal of flood risk management, 11, S434-S443.

Mentens, J., Raes, D., & Hermy, M. (2006). Green roofs as a tool for solving the rainwater runoff problem in the urbanized 21st century?. Landscape and urban planning, 77(3), 217-226

Susca, T., Gaffin, S. R., & Dell’Osso, G. R. (2011). Positive effects of vegetation: Urban heat island and green roofs. Environmental pollution, 159(8-9), 2119-2126.