Gearing up for dry periods

The recent hot weather, parched grass and receding levels at water bodies across Singapore all point to one thing - yet another stretch of dry weather.

Although not as bad as last year's dry spell, it is still the second year in a row the Republic is experiencing such weather conditions, on top of other symptoms of climate change, such as heavier rain and flash flooding.

But there is hope for this concrete jungle. An internationally renowned urban planner has suggested that in built-up Singapore, its buildings could do more to protect the country against the effects of climate change.

At a green conference on Feb 27, Dr Herbert Dreiseitl suggested that buildings could include more green features, and from an earlier stage of the design process.

Water retention tanks could be installed to store rainwater collected during heavy rain. This would not only reduce the amount of rainwater flowing into the public drainage system - thus lessening the chances of flash floods - the stored water can also be used to water plants during a dry spell.

"We have 2.4m of rain coming down every year, we should be able to use this water, and we can, if we have a collection system," noted Dr Dreiseitl, who is director of Liveable Cities Lab.

The German, who founded city planning firm Atelier Dreiseitl (later renamed as Ramboll Studio Dreiseitl) and was in 2011 awarded the prestigious Loeb Fellowship at the Graduate School of Design at Harvard University, is no stranger to Singapore's landscape.

He was one of the designers behind the project to convert a concrete canal in Bishan Park into a meandering waterway with anti- flood features, under the national water agency PUB's Active Beautiful Clean (ABC) Waters programme.

What Singapore has done

The country has experienced more instances of extreme weather, from intense downpours to prolonged dry periods. In 2013, there were 36 flash-flood days, up from 23 in 2011.

During last year's drought, when barely any rain fell for two 27-day dry stretches, PUB was pumping 20 million to 25 million gallons of Newater a day into reservoirs to maintain their water levels. Desalination and Newater plants ran at almost full capacity for more than a month to supply the country with water.

During the current dry stretch, PUB has also injected Newater into the reservoirs.

Over the years, the agency has spent over $2 billion on drainage infrastructure, and more than $150 million a year on drainage improvement projects. This has reduced flood-prone areas from 3,200ha in the 1970s, to pockets amounting to about 35ha today.

But limited space for drainage infrastructure means flood management is an ongoing challenge. The PUB recognises this, which is why it looks at other ways to deal with flash flooding, such as the ABC Waters programme.

It is working with developers of commercial, industrial, institutional and residential projects that are at least 0.2ha to implement measures, such as facade greenery, to slow runoff.

PUB also works to enhance flood protection by installing flood barriers and raised platforms to prevent water from entering buildings.

Sharing space

"One solution is to share spaces, and use mono-functional systems in a multifunctional way," said Dr Dreiseitl. "This could be an area where you hold, filter and keep the water during a heavy downpour, but use it for another purpose during dry weather."

For this, places such as playgrounds and amphitheatres are "highly feasible", said Dr Chew Soon Hoe, council member of The Institution of Engineers, Singapore (IES).

In Boston and Philadelphia, some basketball courts and playgrounds have porous pavements to let water seep through and be stored beneath, or channelled to a storage tank, he said.

But this requires "engineers, architects and landscape architects to work together as early as possible, preferably as early as the design stage, to encompass all requirements including water harvesting and reusing of water".

Layers of green

Another way to boost Singapore's resilience is to introduce layers of green in buildings, instead of, say, just one green roof, said Dr Dreiseitl.

The Parkroyal on Pickering hotel is one example. Its facade is interspersed with green walls and horizontal balconies of plants. When these are part of a system that includes a retention tank, the gardens serve as a filter to purify the water before it is stored.

During a dry season, the water can be used to water the facade greenery - essential for cooling temperatures, attracting biodiversity into the city and contributing to the good health of people.

Facade greenery is feasible, as shown by Singapore achieving its greening target of 50ha two decades before its 2030 deadline, but the use of detention tanks is not yet widespread here.

A spokesman for property developer City Developments told The Straits Times that technical challenges, cost and space constraints must first be overcome.

For instance, a dedicated piping system is required to reverse the pumping up of rainwater from the ground floor to higher levels. That entails long-term running cost.

Situating the tanks on upper floors would be at the expense of "premium, sellable areas", he said. Tanks located on rooftops may also pose aesthetic concerns.

Porous pavements

Porous pavements can be used to slow down rainwater flowing into the public drainage system. Such pavements include those made of pebbles with gaps for water to seep through.

But porous pavements are not feasible for many areas, such as main arterial roads and expressways, due to their strength and safety requirements, said Dr Chew. Such roads must be well compacted to support the load, which means water is not likely to flow through the layers easily.

Porous pavements that are not regularly and properly cleaned may cause ponding over time, affecting driving comfort and safety, he said, adding that such pavements can be considered for minor roads or open carparks.

Moving forward

Implementational issues aside, what is more challenging is mindset change.

"The traditional architectural mindset is to get rid of water as quickly as possible. Water was always seen as the enemy," said Dr Dreiseitl.

"This has started to change... Water is no longer the enemy, it is actually our friend."

This article was first published on March 10, 2015.
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