Building resilience against heat waves through nature-based solutions
As climate change continues to press down on Dhaka, nature-based solutions offer a pathway to resilience, drawing on these age-old insights and the urgent realities of the present
Bangladesh is experiencing one of its hottest years yet, with climate change driving temperatures to new extremes. Urban areas remain unusually hot even in October, while rural regions begin to see morning mist, indicating a seasonal shift.
In April, Bangladesh endured a record 24 consecutive days of scorching temperatures, marking the longest heat wave in its history. This severe weather led to over ten tragic heatstroke deaths and impacted many others, prompting authorities to close schools nationwide for a week as a precautionary measure.
According to the World Meteorological Organisation, a heat wave is defined as a period when daily maximum temperatures exceed the seasonal average by 5 degrees Celsius for five continuous days. Researchers worldwide attribute the recent rise in heat waves to climate change. In Bangladesh, with Dhaka contributing about a third of the country's gross domestic product (GDP) and housing over half the state's job market, the effects of heat waves carry significant economic and social implications.
Research from the Adrienne Arsht-Rockefeller Foundation Resilience Centre found that Dhaka's 2022 heat wave led to an 8% drop in labour productivity, costing Tk66,000 crores annually—a loss projected to double by 2050. Though Bangladesh contributes only about 0.53% of global carbon emissions, it suffers disproportionately from climate change, ranking seventh in the "Global Climate Risk Index 2021" among the countries most vulnerable to its effects.
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The rising temperatures in Dhaka are a stark indicator of climate change's impact, with severe heat waves largely driven by the loss of green spaces, open areas, and wetlands, intensifying these effects. Over the past two decades, Dhaka's average daytime temperature has risen by 2.74 degrees Celsius—significantly above the global average increase of 1.2 degrees Celsius since pre-industrial times and alarmingly above the Paris Agreement's 1.5 degrees Celsius target.
This warming trend has led to Dhaka being labelled a "heat island," a term first coined by scientist Luke Howard in 1818 to describe urban areas that are consistently hotter than their rural surroundings. Rapid urbanisation and industrialisation have transformed Dhaka's natural landscape, with concrete structures and roads replacing greenery, creating surfaces that absorb and retain heat, further intensifying the city's already harsh temperatures.
This urban heat is exacerbated by the extensive use of dark materials like asphalt, steel, and brick, which trap heat, alongside rising air conditioner usage and fossil fuel emissions from vehicles and factories. Together, these factors compound the city's "heat island" effect.
As Dhaka continues to grow, these heat issues are only worsening. In fact, a recent study published in the Lancet found that extreme heat is deadlier than all other climate-related events, earning it the unsettling moniker of the "Silent Killer." Scientists and environmental advocates worldwide are now urging for nature-based solutions (NbS) as a crucial means of tackling this escalating threat.
Environmental campaigns are promoting a reconnection with nature as a path to relief, echoing sentiments voiced by Rabindranath Tagore as early as the 1960s in his poem 'Sabhyatar Proti', where he expressed a profound appreciation for nature and questioned the direction of modern civilisation.
Similarly, Hippocrates, the ancient Greek physician, noted over two millennia ago, "Nature itself is the best physician"—a principle central to environmental conservation today.
As climate change continues to press down on Dhaka, nature-based solutions offer a pathway to resilience, drawing on these age-old insights and the urgent realities of the present.
Nature-based Solutions (NbS) focus on conserving and restoring natural ecosystems to combat climate change while promoting human health, food and water security, and reducing disaster risks. By working with nature, we can enhance biodiversity, protect well-being, and ensure long-term prosperity despite climate challenges. NbS, such as green and blue infrastructure, are vital for stabilising urban temperatures.
Green infrastructure includes initiatives like afforestation, urban greening, rooftop farming, and the development of parks and gardens. Blue infrastructure focuses on restoring and managing water bodies through dredging and community-led conservation of rivers, canals, reservoirs, and ponds. Together, these approaches not only cool cities but also enhance resilience against climate change.
Enhancing green infrastructure in Dhaka calls for a multipronged approach, including increased tree planting, expanded rooftop gardens and urban farms, and the development of green parks. Studies have demonstrated that urban vegetation can significantly mitigate high temperatures; for instance, green parks are up to 5% cooler than their concrete surroundings on a hot afternoon.
Additionally, a Dutch study reported that a 10% increase in urban greenery could reduce the "Heat Island" effect by 0.6 degrees Celsius.
Expanding green spaces, therefore, serves a functional purpose beyond aesthetics—it is an essential strategy for cooling cities.
Trees naturally cool the environment through transpiration, where they absorb water, store it, and release it into the air, cooling surrounding areas. Despite this, Dhaka's tree coverage remains only at 7% to 8%, far short of the recommended 20% for ecological health.
Urbanisation and concretisation have left little space for greenery, making it imperative to maximise available spaces with indigenous, pollution-resistant trees.
Suitable options include mango, banyan, and jackfruit trees, which could line the city's nearly 200 km of roadways, enhancing urban greenery. Studies from the University of Dhaka suggest that banyan trees, with their large leaf stomata, excel at absorbing gaseous pollutants and particulate matter, while shal trees, suited to Delhi's red soil, could also thrive in Dhaka.
Creating more green infrastructure is crucial for cooling, improving air quality, and advancing the city's environmental health. By prioritising native species, we can ensure that Dhaka's urban landscape not only becomes more resilient to climate change but also fosters a healthier, more livable city.
According to global standards, around 10–12% of a city's land should consist of wetlands to enhance livability. However, Dhaka's wetland coverage has dwindled drastically—from 20% of its city area in 1995 to under 2% today.
In Dhaka, green roofs and rooftop gardens have proven effective in mitigating the urban heat island effect by reducing building temperatures through evaporation, shading, and insulation. Plants on rooftops lower heat penetration into buildings, keeping interiors cooler.
This approach also provides shade that reduces roof temperatures, further contributing to urban cooling. Recognising these benefits, the Government of Bangladesh has introduced a 10% holding tax exemption for buildings with rooftop gardens in city corporations and municipal areas, encouraging wider adoption.
These green roofs not only cool the city but also offer residents fresh, locally grown produce, reducing food transportation distances and associated carbon emissions. Many commercial and residential buildings in Dhaka have adopted green roofs, typically covered with herbs and plants around 2 to 8 inches high, which can lower roof temperatures by 2 to 4 degrees Celsius compared to conventional rooftops.
Despite its large urban footprint, Dhaka City, spanning around 306 square kilometres across 129 wards, currently offers only 50 green spaces or parks, most of which are small and often used for commercial activities rather than greenery.
By comparison, New York City, with a similarly dense population, boasts over 1000 parks across 28,000 acres. To address the intensifying heat issue, Dhaka must significantly expand its green spaces and parks, prioritising green infrastructure to create a cooler, healthier urban environment.
Open-water reservoirs and wetlands play a crucial role in urban climate management by absorbing heat, reflecting sunlight, and improving air quality. Reservoirs cool the environment, while aquatic plants help regulate the atmosphere by releasing oxygen and absorbing carbon dioxide.
According to global standards, around 10–12% of a city's land should consist of wetlands to enhance livability. However, Dhaka's wetland coverage has dwindled drastically—from 20% of its city area in 1995 to under 2% today.
Dhaka once had 47 active canals, most of which are now defunct or have disappeared altogether. The city corporations' current climate action plans, aiming to restore 20% of wetlands by 2030 and revive all canals by 2050, are insufficient given the urgency of Dhaka's environmental issues.
Experts advocate for the excavation of the Buriganga, Turag, and Balu rivers and the creation of new lakes in developing areas to strengthen Dhaka's climate resilience.
Dhaka faces mounting challenges due to rising temperatures and frequent heat waves, which, coupled with high humidity, have rendered the city increasingly unlivable. Much of Dhaka's natural landscape—once defined by rivers like the Buriganga and its network of canals—has vanished due to urban expansion and environmental neglect.
Addressing these issues calls for a multi-faceted approach where urban planners, real estate developers, architects, and government officials work together to implement nature-based solutions (NbS). This collaboration is essential to building Dhaka's resilience against extreme heat and the escalating impacts of climate change, ultimately working towards a sustainable, greener future.
Tasneem Chowdhury Fahim, is a lecturer at the Institute of Disaster Management and Vulnerability Studies, University of Dhaka.
Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the opinions and views of The Business Standard.
