A World Bank report titled "A Liveable Future: Protecting Jobs and Growth from Extreme Heat in South Asia's Cities" claims that Dhaka suffers the worst productivity loss due to extreme heat in the region. Rise in temperature causes 3.0 per cent loss of annual work hours, which is equivalent to 465,000 full-time jobs. In terms of economy, the job loss in the country was worth $1.3 to $1.8 billion equalling 0.3-0.4 per cent of gross domestic product (GDP) in 2024 alone. Other studies found that temperature in Dhaka usually stays 5.0 degree Celsius higher than in rural areas of the country. Its ecosystem has been severely disrupted by denudation of its green cover.
The city's urban heat island (UHI) effect caused by trapped higher surface temperature not only negatively impacts the environment but also the health of the city's inhabitants. Studies indicate that indigestion is a common problem. It may cause nervous system disorders like memory loss, depression, irritability and sleeplessness. Another highly negative development is the UHI's thermal impact resulting in circulation of pollution. The thermal impact causes local winds, triggering their migration from suburban to urban areas and in the process bringing back city-contaminated air deposited all around. Thus the urban pollution now becomes further worse. The twin impacts of heat and pollution take a heavy toll on city people, particularly those in the informal sector working in the open merciless scorching sunlight.
By 2080, the loss of annual work hours is projected to rise to 7.4 per cent, equal to 1.65 million jobs. When it happens, it will turn Dhaka's liveability index further worse. By that time climate change is likely to increase global warming and only more so in congested concrete jungles like the Bangladesh capital. Its liveability severely compromised, will it still continue to lure people from rural areas with the hope of some kind of employment opportunities?
In the intervening period many things unexpected can happen. For example, an earthquake if and when strikes, can prove all calculations wrong. If no such natural calamity takes place, will there be a point of no return from an urban conundrum---one that is man-made? Against this background, the incumbent BNP government's plan to plant 250 million saplings all across the country in five years is an appreciable initiative. The government will build green belts in coastal, hill and rural areas. What is important is the proposed use of digital tracking like geographic information system (GIS) and drones. Indeed, post-plantation monitoring and care are crucial to successfully implementing greening and afforestation programmes. Further, the focus on schools and public lands involving students and local community can make the programme successful.
However Dhaka City's case is different and it should be treated so when it comes to expanding its green cover. Many schools in the city have no playgrounds or even compounds. But there are roadside spaces where indigenous saplings can be planted for their growth to maturity. In this connection, reclamation of the existing canals can be a better option. By digging the canals, the dual purpose of retrieval of water flows and plantation of trees on their banks can be served. Two former mayors took up programmes for reclamation of canals and indeed a handful of canals got their uninterrupted water flow back. But before long, the canals were clogged with solid waste dumped into them. Responsible for this is a lack of monitoring and public awareness.
The Lautola canal connecting Mohammadpur and Bosila to the Buriganga and Turag is an example of such mindless human activities. Not only can this vital drainage waterway free the concerned areas from waterlogging but also provide for extensive greening on its two banks. A few canals in the Dhaka South City Corporation (DSCC) can also serve similar purposes. These canals can be developed into local scenic spots under a meticulous afforestation programme. The verdant canopies the trees will grow into will not only offer cooling shade but also positively impact the city's environment.
Besides these green initiatives, another less known afforestation programme known as Miyawaki forest pioneered by Japanese botanist Akira Miyawaki offers a significant solution to the city's UHI. Under this afforestation programme, the technique invented by Miyawaki promotes plantation of saplings very close together, preferably three to five native trees per square metre combining canopy trees, sub-canopy, shrubs and understory layers. The togetherness forces competition to grow vertically for sunlight rather than spreading outward. The growth is 10 times faster than their normal growth.
Happily, two Miyawaki urban forests have already been started in the city's Uttara. One of these is being developed with 53,400 saplings on 2.6 acres of land and the other is with 6,100 trees from 93 native species across 2,285 square metres. Developing more such urban mini-forests may be considered. In old Dhaka, there is no space for such forests but Bosila and Keraniganj on the other side of the Buriganga may be the alternative option. These are dense forests created by man. They become self-sustaining within three years and their high biodiversity in urban and degraded spaces can play a vital role in keeping the environment cool. Together with such initiatives, roof gardens and green covers of building walls with creepers can improve the neighbourhood environment. A combination of small steps like these at the community level and large urban afforestation programmes can cool the city environment significantly.
