Going Green, Building Blocks, Building Cities to Beat the Heat

Our flag is green, and now, to avoid an impending climatic apocalypse our national policies must be green as well, especially when it comes to urban design.

In 2015, an unprecedented heatwave swept over Pakistan, spanning the months of April, May and June, coinciding with the onset of the holy month of Ramazan. Close to 2000 people lost their lives in this event, with the majority of the casualties being in Sindh and in particular Karachi, the capital city of Sindh, where the already soaring temperatures were exacerbated by the “urban heat island” effect, which magnifies the temperatures to a level that the human body, and indeed even urban infrastructure, simply cannot cope with.
While we have been relatively fortunate in the intervening years, our luck is about to run out because this year has seen an unimaginable and unmanageable rise in global temperatures with devastating effects worldwide. The arctic regions of Siberia, not exactly known for hot weather, saw temperatures exceeding 35 degrees centigrade, and a new record for temperatures in Antarctica was also set, with the frozen continent recording an all-time high of 18 degrees centigrade.
Europe sweltered as well, with temperatures hitting the 40’s and climate-change related flooding claiming hundreds of lives. The North American continent also virtually melted in the face of heat, the likes of which they have never had to face; in the Canadian province of British Columbia alone, more than 800 people died in a single week due to the heat and the town of Lytton saw temperatures hit an unbelievable 49.4 degrees centigrade causing a fire that burned down the entire town in just a few hours. This has also been accompanied by torrential rains and floods in China and many parts of Europe, along with wildfires in the American continent.
Make no mistake, this isn’t a one-off event but a sign of things to come, the past six years have been the warmest on record ever since such measurements were first taken and each year sees a new record being set. The question that faces us here in Pakistan is that if this is the scenario in ‘cooler’ and far more well-resourced countries, then what will be our fate? We can already see glimpses of that; in Jacobabad, temperatures briefly climbed to 52 degrees centigrade, a temperature that the human body simply cannot endure and when humidity is factored in this means that the human body’s cooling mechanism (sweating) is no longer effective, leading to deterioration and death. Then there is the risk of other climate-change related catastrophes, like the melting of glaciers leading to more and more flooding.
There’s no doubt that all this is unfair, Pakistan isn’t responsible for the carbon emissions that have led to the climate catastrophe, but will nevertheless pay the price for it as we rank high in the list of countries that are most vulnerable to climate change. The question then is: what can we do to prevent the impending catastrophe? Given the diverse nature of challenges and the impossibility of covering all aspects of this crisis, in this article we will focus purely on urban heat mitigation.
What is the “Urban Heat Island” Effect?
Before doing that, we must understand what the “urban heat island” effect is. We have all experienced that cities tend to be hotter than the countryside. This is because structures such as buildings, roads and other infrastructure absorb and re-emit heat far more than natural landscapes. In urban areas, these structures are highly concentrated and greenery is limited, which means that these areas have a significantly higher temperature than the outlying areas. It’s also a vicious circle. In Pakistan, the higher temperatures in highly dense urban areas lead to an increased demand for air conditioning which in turn makes the heat island effect worse; air conditioning cools the insides of buildings, but releases waste heat to the atmosphere. When you scale this up to the levels we see in urban centers like Karachi, you find that this creates a vicious circle where increased heat leads to an increased demand for air conditioning which in turn leads to increased heat. Factor in that this leads to increased electricity usage and you see how the problem spirals ever outwards. There’s another problem as well, and that is due to the massive air pollution that plagues our cities, several studies have shown that the presence of polluting PM (particulate matter) 2.5 particles in the atmosphere also leads to an increase in trapped heat. If this term (PM2.5) sounds familiar it’s probably because we get to hear about it every year when smog badly affects Lahore and much of Punjab. 
So what should be done? 
Trees, Trees and More Trees
Lets start with the need for trees and vegetation in urban spaces. We have parks in our cities, except of course where these have been encroached on, but for the most part they are in the old colonial design of sprawling lawns which do absolutely nothing to reduce heat. Instead of these, we need more urban forests in which indigenous trees are planted and not fashionable foreign imports. In Karachi, while there was a tree plantation drive some years back, we found that the tree of choice was conocarpus, a foreign invasive species so toxic that even birds do not sit on its branches. Now, to the naked eye this may seem like greening, but the fact is that these varieties do more harm than good. Similarly in Lahore we saw date palms, utterly unsuited to the local environment and aesthetic, planted for purely ornamental reasons in an effort to mimic the desert city of Dubai. It is far better to plant local trees like Neem, which can survive and thrive in our climatic conditions and provide far more benefits that any foreign species ever can.
The science is clear – strategically planted trees can have a major cooling effect on the surrounding areas i.e., streets and roads, which by the nature of the materials used absorb heat, must be lined with trees that can provide shade, thus reducing surface temperatures. In combination with transpiration, even such a simple measure can reduce surrounding temperatures by up to 5 degrees centigrade. The effect on surface (road) temperatures can be even greater; a study in British Columbia during the recent heatwave showed a difference of over 10 degrees centigrade between a tree-lined street and one in which the trees had been cut for ‘development’ purposes. More green spaces in cities also reduce the risk of urban flooding, another regular phenomenon, as these spaces allow water to be absorbed into the soil directly.
Looking at Roofing: Green Roofs
No matter how many green spaces you create and trees you plant, the majority of urban landscapes will comprise buildings, and increasingly high-rise buildings. And even in that there is an opportunity. One, the bare roofs that dot the urban landscape can and should be converted into green roofs wherever this is possible. What does this mean? Green roofs are roofs on which vegetation is planted, and this can range from ‘extensive’, in which hardy plants are used with a soil (or other growing medium) depth of 2-4 inches. Temperatures on such roofs can be 5 degree centigrade lower than regular roofs and the advantage of these are that they require relatively less maintenance and also have the advantage of cooling the building (by providing an extra layer of insulation) and thus saving on cooling costs. The other green roof method is of ‘intensive’ plantation, which includes trees and resembles a park on a rooftop. Of course, this requires a strong building structure and high maintenance, it really may not be feasible in the context of Pakistan where existing buildings will have to be retrofitted.
Looking at Roofing: Cool Roofs
For those without the will or resources to go with green roofs, there is another possibility as well – cool roofs. These are roofs that have been designed to reflect more sunlight and thus absorb less heat than regular roofs and work on a very simple principle; light coloured material reflects more heat than dark material much in the way that wearing white in summers makes you feel much cooler than wearing black. One can make a roof ‘cool’ simply by painting it white (the thicker the paint layer the better) and this is particularly effective in Pakistani cities where we see roofs of concrete (more on the negative effects of concrete later) and in low-income areas or corrugated iron. There’s nothing new about this method, for centuries white roofs and walls have been used in the Mediterranean and North Africa as well. Now, with the invention of highly reflective paints, New York City has recently coated over 10 million sq ft of rooftops with white paint. And white keeps getting whiter, with scientists racing to find the ‘holy grail’ of white paint that can perfectly reflect light and heat with minimum absorption.
Ideally, the ‘coolest’ roofs would be those that employ a mixture of methods; a combination of greening, thick white paint and proper insulation. But this is only a small part of the many measures needed, and if taken in isolation these will not prove as beneficial as when implemented as a policy, and across the board.
Rethinking Our Homes and Buildings
Our cities are largely unplanned, and this is especially evident in Pakistan’s largest city Karachi, where buildings are little more than concrete blocks stacked haphazardly next to each other with no regard for those living in and around them. To some extent, this is unavoidable given our burgeoning need for housing amid a rapidly growing population, but when taken on a large scale and factoring in the subsequent destruction/neglect of green spaces, we find that these mushrooming concrete structures also dangerously exacerbate the already rising temperatures and the heat island effect that has already been discussed. 
Concrete is widely used in construction because it is cheap and easily made; but given that concrete is made of cement, water and sand stones or gravel, it absorbs heat far more than any other building material. When sunlight shines on concrete surfaces, this combination of ingredients goes through a chemical reaction that generates what is called a ‘thermal mass’ that quickly absorbs the heat of the sun. This heat is stored in the concrete, which then slowly releases that heat. During summers this means that concrete footpaths, houses and entire apartment blocks become sinks in which heat is trapped. We can easily see how, on a large scale, this can make entire neighborhoods and apartment blocks unlivable. Now, while the use of concrete may be unavoidable, we can certainly reduce it and replace it with more indigenous materials that have been successfully used in this part of the world for centuries if not millennia. Materials like compressed earth blocks, wood and even bamboo which remain far cooler than concrete and have been successfully used not only in the past, but are also now being promoted once again by modern architects calling on the world to rediscover, and re-adopt ancient wisdom
Naturally, when one hears of buildings with compressed earth blocks (using lime instead of cement) one must ask how durable such a building would be. According to architect Shahid Saeed Khan, an environmentalist and founder of the Indus Earth Trust, the compression strength of these blocks (2000 PSI) is in fact greater than that of concrete blocks (1500 PSI) and are a viable substitute. Not only that, they do not absorb as much water as concrete blocks or brick and hence are less susceptible to water-logging and damage during rains. Most crucially, they keep the temperature in check as well. Mr. Khan has piloted a project building of a modern house with indigenous materials in Gharo, Sindh and displayed temperature readings that show that temperatures inside the structure were a whopping ten-degree centigrade cooler than the outside on a day when outside temperatures hit over 40 degrees. In concrete structures it is the opposite, and sadly in a bizarre quest to attain ‘modernity’ we see that even in areas like Thar and similar regions, where buildings have always been designed keeping the temperatures in mind, locals are opting for concrete structures.
On that note, some of us may recall that at one time old houses in Hyderabad, Karachi and other cities of Sindh would be equipped with windcatchers that would naturally direct the flow of wind into the houses, allowing cool air to enter from the roof-side and the hot air to exit through a series of outlets. Now, these are nowhere to be seen, and thanks to laxly enforced building codes, houses and apartments are built with few windows and are so close together than they simply cannot receive, let alone circulate air. Interestingly, this ‘passive cooling’ design is also found in nature, where giant termite mounds in Africa (also constructed from natural materials) have an internal cooling system similar to the older houses in Sindh. In fact, one Zimbabwean architect, Mick Pearce, used these mounds as a model in buildings in Zimbabwe, which also suffers from many of the same climatic and energy issues as Pakistan. Unfortunately, we are all too eager to ignore the wisdom of nature and even our own past in an effort to build a ‘modern’ future which is quickly looking too costly to be sustainable.

The writer has worked extensively in Pakistan's print and electronic media and is currently hosting a talk show on a private TV channel.
E-mail: [email protected]

Read 376 times