Heat stress doesn't depend on temperature alone

Is this excessive heat that is being felt in Dhaka at present, normal?

Shahiduddin Shahid: There is a heatwave prevailing in most areas of East and South Asia. The temperature in several cities of India is even higher than in Dhaka now. The highest temperature in Bangladesh, such as in Chuadanga, Jashore and Naogaon, remains within 40 to 42 degrees Celsius. There are many cities in India where the temperature is regularly exceeding this. In Odisha, West Bengal and Bihar, the temperature has soared till up to 43 to 45 degrees. In East Asia, the temperature in many cities of Malaysia, Laos and China remains above 40 degrees Celsius at this time. While the temperature in Dhaka is lower than these cities, the heat is felt more here. The reason behind this is unplanned urbanisation more than climate induced. We cannot determine people's suffering in any area due to the heat simply by temperature alone.

So how do we determine this?

Shahiduddin Shahid: Most countries of the world have determined certain ways based on scientific information, to protect their population from the heat. For example, East Asian countries, including Thailand, use a heat index. Alongside temperature, this index has been designed keeping in mind the changes in air movement, humidity, radiation and various climate-related factors. But the Wet-Bulb Globe Temperature concept is gaining popularity in most countries. This concept scientifically highlights the matter of caution against the heat stress faced by people. Through their forecasts, they provide advice on preparing for conditions. In Australia, Malaysia and many other countries, this Wet-Bulb Globe Temperature concept is used to alert the citizens.

Bangladesh's meteorological department still forecasts the temperature and heatwaves. What about the Wet-Bulb Globe Temperature concept?

Shahiduddin Shahid: I have spoken to the meteorological department about this issue. It is important for Bangladesh to forecast the weather on the basis of the Wet-Globe Temperature method. After all, in Bangladesh when the temperature rises to 33 to 35 degrees Celsius, extreme heat is felt. This is because of the extreme heat and humidity. The situation just can't be determined by the wave of heat.

How much danger do we face regarding this extreme heat and humidity?

Shahiduddin Shahid: Summer is becoming dangerous for the people of the entire South Asia including Bangladesh. The number of hottest days in this season is rapidly increasing. Overall, around 66 per cent of the people in South Asia are at risk of the Wet-Bulb Globe Temperature. In every decade between 1979 and 2021, the number of such hottest days during summer is increasing from one day to three days. Such temperature in Bangladesh's southeast region has increased the most. If the temperature in any area is 35° Celsius and this remains for six hours at a stretch, this is extreme heat. Such weather from March till June has been increasing in Bangladesh, particularly in Dhaka.

How has this conclusion come about?

Shahiduddin Shahid: In the sixties when the member of the US army would undergo training during the summer, they would fall sick. It was then for the first time that scientists there tried to determine the heat-related stress and risks faced by people. Alongside the temperature, they took into consideration the humidity, air movement, how long high temperatures remained in one place and from which the direction the sunrays were coming. They created an index out of all these factors, called the Wet-Bulb Globe Temperature. They began using this index to understand how much heat the people were facing and how they were being harmed by this.

Since then the Wet-Bulb Globe Temperature has been used in rapidly expanding cities of the world to determine the weather during summer.

How do temperatures increase due to unplanned urbanisation?

Shahiduddin Shahid: Generally speaking a heatwave is a wave of heat crossing over various regions of the world. This is seen as a heatwave in whichever region it is prevailing. But alongside that heat, if the humidity in the air is high, then the feeling of heat increases. In areas where there are more concrete structures, the daytime sunlight is stored there. So the stored heat added to the heated air increases the feeling of heat. And if there are fewer trees, people do not find shade to protect themselves from the heat. Another problem of unplanned urbanisation is that infrastructure and buildings are constructed in the cities, leaving no space for air flow, thus increasing the heat suffering.

Planned urbanisation is difficult in developing countries, particularly in old towns.

Shahiduddin Shahid: Yes, that is true. But we can take Singapore as an example. Large buildings are constructed on either side of the streets, taking the wind direction into consideration. This facilitates air movement further. Also, after the buildings are constructed, plants and trees are planted on the roofs, walls and in the surrounding vicinities to lower temperatures. They have been very successful at this. Singapore City Corporation has made a rule that at least 80 per cent of the areas of the paths where people walk must have trees so that they people can have shade when they walk. By these initiatives they have managed to lower the temperature of the cities by 3 to 4 degrees Celsius less than the areas by the sea in Singapore.

Singapore is a rich country and they can take up such planned initiatives. How far would this be feasible in Bangladesh, in Dhaka or Chattogram for example?

Shahiduddin Shahid: True, there is the question whether what has been possible in Singapore can be possible in the developing countries of the world. But the concept of 'sponge cities' is fast gaining popularity in many cities of Vietnam, Laos and China. China's Guangzhou is taken as a model of a sponge city. Porous bricks are used to construct various infrastructure of the city, including the roads. Other than plants and trees all over the city, there are small drains all over too. There is a lot of flooding in that city, but because of these small initiatives, the water doesn't stay for long. The water is quickly absorbed by the ground and the groundwater level increases too. As a result, that water plays a role in controlling the temperature in the city during the summer.

A large number of cooling points have been set up on either side of the roads in cities of Vietnam, Thailand, Laos and South Korea. Sitting arrangements have been made at these points along with shady trees and a sprinkling of water. So pedestrians can stop for rest and some respite at these cooling points.

In Malaysia I have seen during the hot days that the city corporation draws up some rules and regulations. For example, the common people can go and spend some time in the air-conditioned malls, shopping centres and buildings. Once they cool down, they can head out again. So these cities have been successful in curbing heat strokes and reducing people's sufferings.

Even in Indian towns like Kolkata and Ahmedabad, there are arrangements for bathing and drinking water at the bus stands, railway station and other public places. The slum-dwellers of the cities, the taxi drivers, hawkers and other low income people could come and use these facilities. Such small initiatives make it possible to protect people from the high temperatures in the cities.

Various steps are being taken in our big cities like Dhaka and Chattogram to keep the temperature under control. Dhaka North City Corporation is planting trees. Water is being sprinkled like rain. It is being said that rickshaw-pullers will be given umbrellas. How effectives will such initiatives be?

Shahiduddin Shahid: Firstly, Dhaka and Chattagram were naturally comfortable cities. But by chopping down the trees, filling up water bodies and carrying out totally unplanned urbanisation, these cities have been made into heat islands. It will be now extremely difficult to create water bodies anew in the cities. But trees can be planted. Planting a few thousand trees in the city will do no good. Trees must be planted along all the footpaths of the cities and in 20 per cent of the new residential areas.  In many cities of the world, rather than planting sapling, they transplant fully grown trees. So within such a few years, these trees provide shade and other service. We have to go in that direction.

Sprinkling water in the roads is just a temporary relief. It may see very appealing, but this is not a solution. Cooling points must be set up at various intervals along the roadsides.

Will it be possible to successfully carry out such initiatives in Bangladesh?

Shahiduddin Shahid: Definitely it will be possible. Rajshahi city is an example. I have seen Rajshahi in the past as a congested and heated city. But over the past decade roads have been constructed in a planned manner in this city, trees have been planted, parks have been created and all sorts of initiatives taken up. All these have beautified the city as well as brought down the temperature. The natural environment of Rajshahi is part of the harsh Varendra region. But initiatives by the city corporation there have yielded much positive results. I feel this is possible in other cities too.

Thank you.

Shahiduddin Shahid: Thank you too.