By Michael Slingsby, Urban Poverty and Climate Change Adviser, South and South East Asia

Most of Bangladesh falls within the warm, humid climate zone. Dhaka and Chattogram are severely affected by urban heat islands and are significantly hotter than the surrounding rural areas. This is due to dense urban infrastructure, a lack of green spaces, and increased heat-trapping materials, resulting in an increase in temperature of up to 3°C in Dhaka. Bangladesh is also affected by cyclones originating in the Bay of Bengal. Climate change-related stresses, including increased temperatures and the length of periods of high temperature. For example, in 2021, there were 49 days with a temperature of over 35°C and in 2024, 65 days. Mean annual temperatures are projected to increase by 1.8°C by the 2060s.

Climate impacts those living in houses constructed of temporary materials such as corrugated iron sheets, particularly children, women, the elderly, and people with disabilities who spend most of their time at home. It also affects those working in exposed situations such as farmers, construction workers and those selling food on the streets. They are negatively affected by a reduction in productivity, loss of working hours and fewer customers during the hottest hours, resulting in a loss of income.

The numbers of those who die as a result of being exposed to high temperatures are difficult to assess, as many also have chronic or severe illnesses, especially heart and kidney diseases. Excessive heat may have a contributory effect on death.

Relative humidity is a factor often ignored, and about 50 years ago, Koenigsberger and others wrote a book, “Manual of Tropical Housing and Building”, which defined “comfort zones” integrating relative humidity and air temperature. Increases in relative humidity reduce the body’s natural ability to keep cool and increase the possibility of heat stroke. This book also includes sections on the design of shading devices.

There are a number of design and heat reduction methods which can reduce the internal temperatures in buildings. Koenigsberger’s book describes the process of heat flow through building materials. A reinforced concrete roof will allow much of the external heat on the roof to pass through the roof, usually at about 2 am, when the occupants hope to sleep in comfort. A ceiling fan will add to the problem by sucking the hot air from the ceiling into the room below. Low-cost apartments often reduce ceiling height to reduce costs, leaving little space between the ceiling fan and the roof, exacerbating the problem.

Painting the roof with reflective white paint can reduce internal temperatures by up to 5°C. See an example from BRAC University’s work in the Karail slum in Dhaka

Building orientation is also important. The smallest side of the building should face west, with the bathroom and toilets on this side. The design of shading devices to minimise the exposure of windows and doors to the sun to remain and to remain in the shade is important.

Disclaimer: The views expressed in this piece are those of the author/s and do not necessarily reflect the views or policies of AIDMI.