That Ho Chi Minh City has become noticeably hotter in the past decade has yet to be confirmed by any official statistics, but look at other cities around the world and you can see this urban area following a similar trend. Take Tokyo, for example. Its average temperature in September over the past 100 years has increased from 21.5 °C to 24.5 °C. This is a result of the urban heat island (UHI) effect, where human activity and the modification of the land surface due to urban development makes the city become significantly warmer than its surrounding rural areas.
There are a number of causes. Building materials, such as concrete or asphalt, effectively retain heat as do dark-coloured pavements or roofs, thus causing a cauldron-like effect. Waste heat generated by energy usage is another contributor, something that can be measured with the growing use of air-conditioning. In Saigon at the turn of the millennium, few families could afford the luxury of these cooling machines. Now, especially in the city’s central districts, the air-conditioner has become the norm rather than the exception. While it cools air indoors, by spitting out hot air, outdoors it warms it up.
Another reason for the hotter city is the lack of evapotranspiration, something that results from not having enough vegetation. The sum of evaporation and plant transpiration from the earth’s land surface back into the atmosphere, this process is responsible for 15 percent of the water vapour in the earth’s atmosphere. Like sweat, it’s a cooling process. Drive through the park on either side of Truong Dinh or Le Duan, and thanks to the vegetation and the canopy caused by the 100-year-old trees, you instantly notice a cooling and dampening of the air. A lack of vegetation means that there is no natural cooling process installed to cool down the city when it gets too hot.
Green it Up, Baby
What this all means is that to cool the city down, Saigon really needs to start going green and find a way to counteract the heat island effect. Yet much damage has already been done — trees and green areas have disappeared to make way for new developments. And many of the latest constructions in this metropolis are far from green. Nonetheless, it is not irreversible and over a period of time, steps in the right direction can still be taken.
One route would be to move towards using white or reflective materials to build houses, roofs, pavements, and roads, thus increasing the overall albedo, or surface light reflection, of the city. Using light-coloured concrete has proven effective in reflecting up to 50 percent more light than asphalt. This in turn reduces temperatures.
A second option is to increase the amount of well-watered vegetation and trees along roadsides or highways, and to ensure that areas being developed have parks. Green roofs are also a good option. Excellent insulators during the warm weather months, the plants cool the surrounding environment and help improve air quality by absorbing and converting carbon dioxide to oxygen.
More shaded walkways, buildings constructed with better airflows, reflective glass and less dependency on air-conditioning — all would contribute to the decreasing of the temperatures outside.
But until there is a solid movement in place and a whole-hearted, universally accepted desire to green up this city, the dry season will continue to be excruciatingly hot, with the heat waves becoming unbearable.