Green rooftops and permeable pavements can help reduce risks of floods


  • Letters
  • Monday, 27 Apr 2020

A permeable paver demonstration in Tasmania, Australia. Permeable pavements allow rainwater to soak into the underlying ground, preventing surface runoff from accumulating and flooding. — JJ HARRISON/Wikimedia Commons

Now that we are finally taking a breather from water scarcity and rationing, we are confronting increased flood risks brought by the south-west monsoon, as evidenced by the recent floods in Petaling Jaya, Penang and Kedah. Echoing Sahabat Alam Malaysia president Meenakshi Raman’s call to create “sponge cities” (“Create sponge cities to prevent flash floods, says SAM”, The Star, April 22), I would like to reiterate that it is imperative for us to pursue climate change adaptation more vigorously now. It is time to move from traditional flood mitigation measures, such as river deepening and drain maintenance, to sustainable urban water management.

There are many successful urban water management approaches for us to emulate and learn from, such as the “Active, Beautiful and Clean Waters” in Singapore, low-impact development in the United States, "Sponge City" in China, a sustainable urban drainage system in Britain and water sensitive urban design in Australia. They all share a main objective: to make urban environments resilient to floods.

A common feature among these approaches is green infrastructure, a network of natural landscapes or habitats such as wetlands, parks, rain gardens, green roofs, green roads and green parking lots, all designed to provide specific ecosystem services. I would like to highlight two green infrastructure options: green roofs and permeable pavements.

While it is preferable to have more recreational parks and fields in cities, land scarcity and exorbitant land prices are a major hindrance. Green roofs are a cheaper and feasible alternative, especially given the substantial number of unused roofs in cities. Having plant beds on otherwise unused rooftops helps to intercept rainwater and reduce runoff. This is particularly effective in delaying peak flow, allowing the city's drainage systems more time to remove excess rainwater, thus reducing flood risks.

For urban planning in Malaysia, the concept of interlacing or intersecting buildings should be studied. By stacking blocks upon each other irregularly, a larger surface area is available for green roof implementation, leading to a higher rainwater interception rate and, subsequently, lower flood risks. It is very likely that interlacing buildings will become a common feature in future sustainable cities.

Instead of the prevalent tarmac roads, permeable pavements should be prioritised. Permeable pavements allow rainwater to infiltrate into the ground, preventing surface runoff from accumulating, thus leading to lower flood risks.

Although permeable pavements tend to perform better in a drier climate, it is found that permeable pavements can still reduce up to 70% of runoff volume in the wet climate of Hong Kong. However, performance is dependent on paving materials. Permeable concrete is one of the best permeable materials for pavement construction because it does not allow water clogging. These factors should be taken into consideration before constructing more permeable pavements in Malaysia.

What truly makes green infrastructure appealing, however, is not only its flood mitigation potential but also the slew of co-benefits it brings, such as urban beautification, biodiversity conservation, water and air quality benefits, urban heat island mitigation, and carbon sequestration.

Nonetheless, it would be ill-advised to push for a widespread implementation of green infrastructure. Instead, to ensure effective resource utilisation, we should adopt a risk-based approach and target flood-prone areas specifically. This means that we should prioritise green infrastructure investment in flood-prone areas where it is possible to achieve a high reduction in flood risks.

Ideally, a pilot project should be conducted in a major city that is plagued by recurrent flash floods first, for example, Kuala Lumpur. To start the ball rolling, the federal government should come up with a national policy for developing flood-resilient cities and provide incentives to encourage public participation (eg, tax relief for private corporations that invest in green roofs). The policy implementation and master planning can be delegated to state and local authorities, with a self-assessment mechanism in place to allow evaluation and monitoring.

Bear in mind, however, that green infrastructure will not eliminate flooding completely, it can only help to reduce floods risks, and that the frequency and intensity of extreme precipitation events will gradually increase in response to climate change.

The coronavirus pandemic is a grave wake-up call to humanity. While the pandemic and climate change are two fundamentally different crises, there is one significant lesson that we should learn from the pandemic and apply to how we tackle the issue of climate change: If we fail to plan, we are planning to fail.

TAN WIN SIM

Melaka

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Climate change , floods , resilient cities

   

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