Green spaces in a city

 If you live in a city, walking the dog, cycling, going for a run, or even just sitting reading can be much more exhilarating in a really large green open space. This is even more the case in a city like Johannesburg, which is totally landlocked, with no large expanses of ocean or mountain to relieve the oppressiveness of the "concrete jungle". But the pleasure of engaging with nature in a large area of parkland is just one of many benefits that such an amenity provides in any city.

Delta Park looking towards Rosebank

One of my favourite green spaces is Delta Park in the north of Johannesburg. It has an interesting history, in that it was the location of the sewerage works for this section of the city from the 1930s until the 1960s, when this function was removed to the northern boundary of the city. The original administrative and primary treatment building, in the Art Deco style, still exists, commemorated by a Blue Plaque. Some of the walling of the original settlement ponds can still be seen, now covered in colourful graffiti. The extensive lands around this infrastructure were used as the final stage of water purification before percolating into the subsoil and the river that runs through the park.

Since it has been converted to parkland, it continues to serve important functions in the city, as do the other large open spaces. One of these is storm water management: parks in many cities around the world are located on water courses, capitalising on land-use planning that often requires a swathe of open space alongside a river, clear of all building, in case of flooding. Some cities also use this open space to discharge storm water from surrounding roads and built-up areas, with a twofold benefit over a completely piped system in that it allows the rain water to recharge the natural water course and percolate into the subsoil to feed the aquifer, the water that runs several meters below the land surface. 

In cities such as Curitiba in Brazil, this area along many of the waterways was occupied by informal settlements, which were relocated to higher ground to allow the space to be actively used in flood control and to improve the safety of residents. This method of natural flood control, rather than building more and larger concrete piped infrastructure will become increasingly important as we confront extreme rainfall events as a result of climate change. 

Parque Barigui, Curitiba
Creative commons licensed: https://www.pexels.com/photo/view-of-the-parque-barigui-and-skyscrapers-in-the-background-curitiba-brazil-19220189/

Cities are serious contributers to climate change: they are generally made up of dense materials such as concrete and steel, especially in the high-rise parts. These materials heat up during the day, but store this heat and radiate it back into the atmosphere, making the city much hotter than the surrounding countryside. The prevalence of dark surfaces (here, roads are the big culprits) also contribute to the absorption of heat. This creates a bubble of hot air above the city, forcing the air to rise, and the sudden cooling of the air forces rainfall directly over the city where it exacerbates flooding, and prevents it falling over the surrounding agricultural and natural spaces where the rain would be beneficial.

Creative commons licensed: https://sketchplanations.com/heat-islands

While small areas of vegetation, such as green roofs and small city parks, can help to alleviate this effect, it is only the really large expanses of green that make a significant difference. Evapotranspiration of the plants also helps to regulate the humidity in a city, especially important in a city such as Johannesburg, with its long periods of no rain through the winter.

Pollution in cities, especially through vehicle fumes, is reduced through the presence of vegetation, with its ability to absorb carbon dioxide and release oxygen back into the atmosphere. This is but one of the important biological functions that green spaces provide in a city, along with encouraging biodiversity of a wide range of plant and animal species. In several cities, there is a concerted effort in creating continuous green spaces - corridors of vegetation that allow an even greater variety of birds and animals to co-exist in the city. This can sometimes have interesting outcomes though - I am reminded of the recent sighting of a baboon on Northcliff hill in the completely built-up suburbs of Johannesburg!

One of the reasons that I have chosen to focus on large open spaces in cities, is that they are constantly under threat of development. Especially in the inner parts of a city, land values tend to be high, a tempting opportunity for the landowner (often a public body such as the municipality) to sell off some or all of the land. As cities become more compact and densified, these green spaces play more and more of a role in tempering and regulating natural processes, which will become even more critical with climate change. 

One of these areas currently threatened is the vast area around Melville Koppies and Emmarentia Botanical Gardens. Not only does this open space provide the environmental services that I have described, but it also contains important archaeological sites and a large tract of indigenous vegetation. If you want to sign the petition to save this public open space, the form is at: https://docs.google.com/forms/d/e/1FAIpQLSezYzDin1T6U05P43WtdJfqt_7PndGisERef7iN4cAt31Bldg/viewform