Climate change is real, but so is increased urbanisation as a factor in the recent flash floods

Last Saturday (17 April), Singapore experienced flash floods due to prolonged heavy rain, causing the water levels in a number of drains and canals on the island to exceed 90 of its capacity.

Following that, Minister for Sustainability and the Environment Grace Fu said on Monday (19 Apr) that Singapore has been getting a lot more intense rainfall recently, one of the highest in the last 40 years. These intense rainfall are also occurring more frequently, she said to reporters on the sidelines during a visit to one of the Deep Tunnel Sewerage System (DTSS) sites.

“It shows us the importance of planning for climate change and also mitigation,” she added, noting the S$2 billion already spent by the Public Utilities Board (PUB) on drainage improvement works over the last 10 years.

The minister said that another almost $S1.4 billion will be spent in the next five years on such projects. Ms Fu said that that 37 ongoing projects, with 10 more due to commence this year including drainage works in Selatar North Link and Serangoon Avenue 2 and 3.

This shows our determination to improving our water infrastructure, increasing our climate resilience, and also making us more resilient in a changing world,” Ms Fu asserted.

When asked why flash floods still occurred in Singapore despite investments into the country’s drainage system, Ms Fu pointed to the effect of global warming on changing weather patterns.

She said, “We have already been witnessing pattern changes, and we expect to see even wetter and drier patterns going forward.”

According to PUB’s Facebook post on Saturday, western Singapore saw its heaviest rainfall from 12.25pm to 3.25pm of 161.4mm. This is about 91 percent of Singapore’s average monthly rainfall for the month of April. It is also in the top 0.5 percent of the maximum daily rainfall recorded in Singapore since 1981.

PUB issued flood risk warnings for over 20 locations, including Sime Darby Centre, Bukit Timah Canal (Leng Kwang Baptist Church), Ulu Pandan Canal and Sungei Pandan Kechil (NUS and AYE).

Ms Fu highlighted the DTSS network of underground sewers as an example of the government’s long-term planning to prepare for the effects of climate change.

She explained, “The DTSS allows us to capture and reclaim the water. If we are able to reclaim more, it makes us more resilient because our water can be reused over and over again.”

While it is inarguable that global warming has led to changing weather patterns which in turn has caused increased rainfall in Singapore, it should be noted that increased urbanisation is a key factor in this issue as well.

According to the PUB’s report on Key Conclusions and Recommendations of the Expert Panel on Drainage Design and Flood Protection Measures in 2012, “Urbanisation has undoubtedly led to an increase in storm water runoff in Singapore.”

The panel which was tasked to look into the cause of the flash floods at Orchards in June 2010 and June 2011, noted that other than generating higher and faster surface run-off, “increased urbanisation may also bring about other impacts such as increased heat production, changes in rainfall patterns, and other climate change impacts.

Though it also added that further modelling and analysis is required to determine the extent of this effect of urbanisation on flash floods, particularly in the Stamford Canal Catchment.

As Singapore steps up its effort by building more drains, the rate of building over open soil has also increased over the years.

So while it is true that global warming is one factor for the recent and more frequent flash floods plaguing the island, it would be unwise to sidestep the severe impact that urbanisation — cutting down of trees in green space and covering the soil up with concrete — has on climate change, and in turn, flash floods.