Saving the vegetative cover of an urbanising Accra
Urbanisation in Sub-Saharan Africa is occurring at a time when fertility rates are high and mortality rates are low, unlike what transpired in the United States in the late 19th century and early 20th century fueled by industrialisation. From a low figure of 190,000 in 1957, Accra’s population is now estimated at 2.2 million and projected to reach four million by the year 2020.
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The rapid rise in the city’s population has been accompanied by a greater desire for housing facilities. However, the horizontal growth and the preference for single family detached housing has resulted in low density developments in many new communities in Accra. This does not do much to improve the housing deficit in the capital yet it is having debilitating effect on the city’s vegetative cover.
I have observed with much concern a developing trend accompanying the sprawling problem Accra is facing. Some of the new residential, educational and commercial facilities in the city have their entire compounds (front yard, rear yard and side yards) landscapped with floor tiles, pavement blocks or granolithic screed with scanty greenery. The construction of roads and parking lots accompanying this horizontal growth have resulted in the city’s vegetation cover gradually being eroded.
Sadly, asphalt and paving blocks are materials that absorb more of the sun’s rays than vegetation and preclude the infiltration of rainwater in soils. This results in a reduction in ground water recharge and further lowering of the water table as well as contributing to an increase in ambient temperature and a decrease in relative humidity.
It is particularly worrying because among the guilty are the rich, educated, poor, illiterate and, surprisingly, some built environment professionals, the very people who are in the know of the consequences of such practices in a climate change era.
The increase in intensity of extreme weather (variable rainfall pattern, extreme temperatures) and acceleration of sea level rise as a result of climate change has necessitated urgent measures to make cities resilient.
With Accra being a coastal city, such bad practices will not enhance its resilience. As Accra continues to sprawl and vegetative surfaces are eroded, the natural dispersion of water into the sea or rivers or ground will be greatly distorted. There will be an intensity of rainwater run-off and, flooding, siltation and water pollution would likely be the end result. This will contribute to the severity of the perennial flooding experienced in Accra.
Maximising urban tree canopies, which is made up of leaves, branches and stems of trees that cover the ground when viewed from above, is the key to reversing heat island proliferation. Wind resistant and flood resistant trees and vegetation enhances the resilience of a city. Often known as nature’s air conditioner, (trees greatly reduce air pollution) as it is able to filter dust particles and sequester carbon dioxide by absorbing it from the atmosphere.
Depending on the leaf shape and density of foliage, trees are able to intercept, and absorb solar radiation leading to lower air temperatures. Research has shown that, a single tree is capable of transpiring 400 liters of water per day, provided there is sufficient soil moisture. Trees are thus able to affect the micro climate of neighbourhoods positively.
They create sheltered zones within the urban environment for outdoor activities. Trees near walls and windows provide shade and result in provision of effective protection from solar heat gain, and serve as wind breaks when they are planted in specific locations.
Trees and vegetation have healing effects on urban dwellers, confirmed in 1981 through a study by Roger Ulrich. In his study, patients recovering from gall bladder surgery were subjected to a test. One group occupied hospital rooms with views of trees and nature, and the other group with views of walls. At the end of the study, patients with the views of trees and nature were found to recover more quickly and they took fewer doses of analgesics. The relevance of trees to the urban population of Accra cannot be in doubt.
A concerted effort is required to create urban parks, neighbourhood parks, park cool islands while protecting what already exists. Additionally, vertical growth should be the solution in dealing with the urban congestion in Accra.
Horizontal growth or sprawling should be discouraged since it puts development pressure on limited land area of Accra. Landscape architects should be employed to undertake residential landscaping to ensure a good balance between soft landscaping and hard landscaping. Residents need to consider the future generation in our quest to conquer undeveloped land in the capital city.
Enough wounds have been caused to the landscape of Accra already so the time to act is now. The government of Ghana can secure public ownership in high hazard and risky sites in Accra by use of compulsory acquisition or conservation easement.
This move will take these lands of the development market, preventing the future exposure and vulnerability that development will cause.