Limiting hard-paving and using a shade of the right material, colour and technique can be smart additions to urban design of public spaces
This is the second of a two-part series on effective planning to make cities cooler. Read the first part.
Different strategies or their combinations may be applied for reducing heat build-up in open urban areas, depending on the kind of space. The first strategy should be minimising hard-paved surfaces. These non-permeable surfaces absorb heat and slowly release it, making the atmosphere around warmer. In areas where this becomes a necessity, permeable pavers may be used; the vegetation growing in the voids helps with evapotranspiration, thus cooling the surface.
Permeable pavers absorb less heat. All photographs provided by author
Shading can be among the most effective strategies in ensuring the heat doesn’t reach the ground in the first place. Buildings with courtyards may employ devices such as space frames that can effectively cut down direct sun and help in shading not just the ground but also the vertical surfaces. The effectiveness of such a device can be seen from images with and without the space frame. (Both images were taken in June).
Space frame acting as a shading device at India Habitat Centre, Delhi. Unshaded (left), shaded (right)
CSE’s 2023 compilation of case studies The Cooling Web captured some of these strategies applied by different campuses across India. Here are some of the things to keep in mind:
Getting the shading material right: The materials of the shading device is another critical thing to take into account. A white-coloured material will reflect more sunlight than a dark one. Similarly, a lighter material such as a fabric will absorb and retain less heat than a denser material.
A lighter coloured fabric reflects direct sunlight better than a darker one
Seasonal appropriateness: Much of India also experiences moderate to extreme winters. Hence, it is critical to get the shading device right so that it allows the winter sun, while blocking the summer sun.
The shading device at the India Habitat Centre in Delhi is designed in a way to optimise sunlight penetration according to seasonal variations. During winter, the sun is at a lower angle in the sky, allowing the device to permit sunlight to enter, warming the interior spaces. In contrast, the summer sun is higher and more intense, and the device’s shading fabric is angled to block this harsher sunlight.
This strategic use of the fabric’s angle helps to keep the building cool in the summer while allowing beneficial sunlight during the winter, enhancing comfort and energy efficiency year-round.
Winter sun penetrates inside during early December
Height and mass matters: A shading device after absorbing the heat will radiate it back to the surrounding atmosphere, including back towards the ground. Getting the height correct, hence, will matter. A low-height shading device offers shade but can also radiate the heat back to the ground and towards the person using the space. This is particularly detrimental if the shading material used is high mass material.
A low height-high mass shading device radiates the heat back towards ground
Trees combine multiple advantages: The use of these shading devices should be restricted to only certain areas where trees are insufficient. The strategic placement of trees offers numerous benefits above artificial shading devices. Beyond providing ample shade, trees facilitate evapotranspiration through their leaves, which helps cool the surrounding air.
The area around the tree trunk can be utilised at ground level, creating functional spaces such as seating or pathways. Meanwhile, the tree’s canopy serves as a natural shading device, reducing temperatures and enhancing the comfort of outdoor areas.
The land around the tree is permeable hence it provides the added advantage of cooling. Lastly, no artificial device can match the fact that trees act as massive carbon sinks.
Where to begin
An exercise should be carried out by the local bodies for recognising and de-concretising urban areas that can do without hard paving. This includes public spaces, streets, among others.
The latest version of the Energy Conservation and Sustainability Code (ECSBC) recognises the importance of permeability and has included it into the latest draft version of the code. “Paved areas, including parking areas and pathways of the site, shall not exceed 30 per cent of the total site area excluding building footprint or as per local bye law, whichever is more stringent.”
Source: Latest draft of ECSBC
The streets provide a massive opportunity for installing shading strategies, around 15 per cent of a city’s land is generally streets. The medians and other unutilised portions of these streets provide ample space for trees to be grown.
A study by the Indian Institute of Technology Delhi evaluated the walkability of streets in the city during extreme heat conditions. The findings revealed that over 67 per cent of the audited streets lacked adequate shading, significantly affecting the comfort and safety of pedestrians during intense heat.
Implementing tree plantations around these streets offers multiple benefits, including providing essential shade, helping cities achieve their greening targets, and encouraging people to walk instead of using vehicles. This reduction in vehicle use can decrease anthropogenic heat, which contributes to the urban heat island effect.
Areas with a high concentration of hawkers also serve as rest spots for labourers and other people using open areas, making them ideal for prioritising the implementation of shading, deconcretising and water features.
Enhancing these areas with tree canopies or shading structures provides much-needed relief from the sun, improving comfort for both hawkers and workers. Deconcretising these spaces, by replacing hard surfaces with permeable materials, can reduce heat absorption and promote natural cooling through evapotrasnpiration. Incorporating water features, such as fountains or misting systems, can further lower temperatures and create a more pleasant environment.
Strategic placement of trees can provide ample shading
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