The urban climate change conundrum
People, ecosystems and the economy are all at risk
One of the fundamental cornerstones of progress of a country is urbanization. The term "urbanization" is closely linked to the term "development". Bangladesh has a high urbanization rate (Ahmed and Ahmed, 2017), and it is visible that the country is rapidly developing. The transition from an under-developed to a developing country was not easy. However, these advancements came at a price. Change in temperature is one of the outcomes of that price.
The climate of Bangladesh was not the same half a century ago. In recent years, there have been considerable temperature fluctuations. During the last few years, Bangladesh's weather has been rapidly altering, reaching a critical point. Between the years of 1976 to now, Bangladesh has had an average temperature increase of 0.5°C. The rise in maximum temperature has not been consistent throughout the country. For example, maximum temperatures in the eastern portions (Chattogram and Sylhet divisions) of Bangladesh rose by 0.9°C, compared to a 0.5°C rise in the central parts spanning Dhaka and nearby districts. As a result summers are elongated, winters are warmer, and the monsoon is becoming increasingly unpredictable.
Rapid urbanization creates a significant impact on urban land use and land cover , increasing the land surface temperature. Land use and land cover fluctuations are intimately linked to variations in land surface temperature and the intensity of Urban Heat Islands (UHI). The UHI phenomenon is caused by the fact that urban regions have greater air and surface temperatures than rural and suburban locations. The UHI effect arises as buildings, roads, and infrastructure absorb heat, causing temperatures in urban areas to be 1 to 7 degrees Fahrenheit hotter than in outlying areas. Although the impact is greater during the day, the slow release of heat from infrastructure overnight can keep cities substantially hotter than surrounding locations.
Heat waves work as one of the indications of climate change in urban settings. When the daily maximum temperature in a large area exceeds 36 degrees Celsius, a heat wave occurs. Considering Bangladesh's major districts have growing populations and often lack the capacity to control the effects of rapid urbanization, an increase in urban temperature has both direct and indirect effects on the people. The heat wave has covered the entire divisions of Dhaka, Rajshahi, and Khulna. The maximum temperature was recorded at 41 degrees Celsius this year in the country.
Urban areas are already warmer than surrounding non-urban areas due to the heat island effect, people living in cities are at a higher risk of being affected by heat waves. Heat waves and heat exposures both have their negative consequences on human health. Heat waves can be lethal, especially for those who engage in outdoor activities in direct sunlight without properly hydrating. Due to a lack of water availability throughout the summer days, pollutants in the water become concentrated, and as people consume more water during this period, many water-borne diarrheal diseases emerge. In addition to that the body's cooling function is also hampered by humid air, which slows perspiration.
Increased urban population is another element that contributes to rising urban temperatures. People are migrating from rural areas to urban areas in search of a better future and like any other developing country Bangladesh's urban populations are seeing a significant increase in the number of migrant dwellers. The growth of the urban population is primarily due to rural-to-urban migration and the majority of migrants are rural poor who seek refuge in slums, squatter camps, footpaths, train stations, and other dispersed locations. The urban environment is being impacted by this rural-urban shift.
A livable city should contain at least 25% greenery of its total area but in the case of Dhaka, it barely has 5% due to not only lack of regular plantation and care of existing ones but also to accommodate the city's growing population. It is undeniable that rural climate adaptation is required, as the effects of climate change in rural areas are considerably more obvious than those in urban areas. However, adaptation measures in urban areas are also necessary since the impact of climate change may not be instantly evident but it is progressively impacting the urban environment. The rising temperatures in recent years have demonstrated that if we do not take the essential steps now, it will be impossible to live in these areas in upcoming years. People, ecosystems, and the economy are all at risk as a result of rising temperatures across the country.
Urban areas are already warmer than surrounding non-urban areas due to the heat island effect, people living in cities are at a higher risk of being affected by heat waves. Heat islands will become more pronounced in upcoming years as urban population densities rise and natural land areas decrease. For heat stress management, Nature-based solutions (NbS) can play a pivotal role in the country's heat action strategy. NbS solutions like “Blue and Green Infrastructure'' offer cost-effective solutions to reduce the impact of heat waves and urban heat island effect. Blue-green infrastructure refers to the use of blue features in urban and land-use design, such as rivers, canals, ponds, wetlands, floodplains, and water treatment facilities. And as green elements, trees, forests, fields, and parks are included. Communities may address and respond to some actions, for example green infrastructures like green roof, vertical greenery which can minimize heat island temperatures and lessen city people's exposure and vulnerability to climate change impacts. Planting trees like Eucalyptus, Sissoo, and Akashmoni throughout the country's periphery was proven to be a wrong decision in the past, as these trees were planted as fast-growing, shady trees with commercial value, but the thirst of their roots and their ability to cause a decline in the underground water level was overlooked. So, it is also essential to plant adequate trees that have the intended effect of decreasing heat in the atmosphere and providing environmental benefits.
For instance, Debdaru tree, also known as False Ashoka , is an excellent source of air purification. The heat exposure in the atmosphere can be reduced by planting more of these trees along the roadside. As blue infrastructure, it is also necessary to preserve the remaining water bodies like lakes and wetlands etc in the urban area. Water bodies in an area are responsible for potential cooling by evaporation, which reduces the heating effect. As the frequency, severity, and duration of heat waves are expected to grow as a result of climate change, it is essential to implement adaptation measures as soon as possible; otherwise, focusing solely on development may jeopardize the survival of humanity.
Kazi Taiba Bari Nowsheen is working in the International Centre for Climate Change and Development (ICCCAD) as a research intern, her research interest lies in Climate Change and DRR. Can be reached at [email protected]