The rainy season that officially began last May, together with the La Nina effect, brings unusually heavy rains that leave several areas inundated. Worse, the climate change impact intensifies weather turbulences with intense, localised rainfall — known as “rain bomb” or cloudburst — that may cause severe floods in the area with poor drainage system. 

We have to say, the Bangkok Metropolitan Administration (BMA) did quite well preparing for heavy downpours in the past months, i.e., dredging canals, removing waste from waterways and cooking fat from drainage pipes. There are active flood tunnels, and some are under construction. Yet, several areas still remain flood prone. The sight of rain-related paralysed traffic underneath and on the Bang Na-Trad expressway, with a backlog stretching 31 km long, in a major rain event late in May was indeed horrible.  

Undeniably, rainy events remain a threat for several parts of Bangkok as the city is not porous enough. It’s time for a change. 

Over the past years, urban porosity — an increase of green spaces, permeable surfaces with the use of porous asphalt/concrete — has gained more attention from city planners around the world. Green areas include rain gardens and vertical as well as rooftop gardens that help retain and capture water in a heavy rain event, so that it will not overwhelm the drainage system. By accommodating porosity, the city will not have to solely depend on the conventional drainage system.  

Several cities around the world have adopted urban porosity strategies to cope better with floods. Shanghai and Wuhan, for instance, have embraced such a strategy. In effect, they increase green spaces, water-retention areas, and permeable surfaces for roads as well as footpaths. 

In Europe, Copenhagen has implemented a plan to tackle cloudbursts, by spreading rain gardens around the city. There are also bioswales — a shallow, vegetated channel that helps manage stormwater runoff by capturing it into the ground. 

Other cities not far away from Bangkok also adopted this strategy. Singapore, for example, has increased green areas. More importantly, Singaporean city administrators engage the private sector in the tree planting and vertical garden campaign. Although such a strategy aims primarily at reducing the heat island effect, it also accommodates urban porosity significantly. 

It should be noted that, while adopting a porosity strategy, these cities do not totally abandon conventional water management systems that include the use of water pumps and drainage pipes. In fact, such a system still remains the backbone of water management, and it requires standard maintenance to maintain, if not improving, its efficiency. 

In fact, the ideal water management system must ensure joint operation between the green and blue infrastructure (meaning extensive green space and water retention area) as well as grey infrastructure (or water drainage system). 

But if we look at Bangkok, we have to ask if it’s time for the BMA to improve the city’s drainage system by incorporating more blue-green infrastructure to ensure more porous surfaces so as to drain the rainwater more efficiently.

Some questions arise: What can be done so that the city will have more rain gardens, like Chulalongkorn University Centenary Park and Benchakitti Park, that have the capacity to capture and filter water in other parts of Bangkok?  

In addition, now that some footpaths are paved with porous asphalt/concrete, what can be done to ensure that city administrators shift to sponge-like material when constructing or renovating city footpaths and some roads, while more tall buildings set aside area for rooftop or vertical gardens? 

To see this happen, it’s necessary for the state, i.e. the central government and the BMA- to set a long-term strategy to increase the presence of pores in the city. The state may offer incentives in the form of tax as well as financial support for the private sector and the public, so that they accommodate green infrastructure, which in effect will increase water retention areas. 

Increasing city porosity can be a co-benefit as it will solve flood problems and, at the same time, secure more green and recreational areas that will help tackle pollution and heat island effects.  Such a co-benefit measure is by all means considered economically cost effective. 

With regard to city development, it’s time Bangkok increases porosity a key measure against climate challenges. It will also help increase city people’s quality of life. If done, city people will not have to worry that roads will turn into canals anytime it rains. 

Nuntachart Ratanaburi is a researcher at TDRI. Policy Focus from the TDRI appears in the Bangkok Post on alternate Wednesdays.