SINGAPORE - Urbanisation was officially acknowledged for the first time yesterday as part of the reasons behind the increase in storm water run-off, as the expert panel on drainage design and flood prevention measures revealed its recommendations on flood mitigation in Singapore.

"Urbanisation has undoubtedly led to an increase in storm water run-off in Singapore," the panel said in its statement. "There is therefore a strong argument for introducing measures to mitigate the effects of such urbanisation."

However, the panel - formed in June last year after flooding in the Orchard Road area in 2010 - stressed that these effects are often "complex" and will require further analysis.

The 12-member panel's recommendations include more dynamic weather modelling and infrastructural improvements, but it noted that a whole-scale up-sizing of Singapore's drain infrastructure would be expensive and disruptive.

A "better approach" was to reduce and delay run-off at source such as with storage tanks, rain gardens, roof-top gardens and porous pavements.

"We would like regulations brought into Singapore which require new developments to install source-controlled measures, so that the impact of development is mitigated," said panel member Professor David Balmforth, executive technical director of MWH UK, an engineering firm. "We also believe there's potential of retrofitting these measures to existing buildings."

These measures are to be complemented with diversion canals, storage tanks along "pathways" of drains, drain capacity improvements, and finally, flood barriers, raised platform levels - some of which is already being done, but "could be carried further", noted Prof Balmforth.

When contacted, the PUB said it will be studying the recommendations of the panel.

Minister for the Environment and Water Resources Vivian Balakrishnan had announced in Parliament on Monday that the PUB was looking into raising the capacity of Stamford Canal to reduce the risk of flooding.

Asked whether this would run counter to the panel's recommendation, Prof Balmforth said: "It would be unusual to produce a range of measures in a city that didn't involve some upgrade of some conveyance capacity somewhere, but that's not the same as investing in wholesale capacity upgrade of the city area, that's an important distinction to make."

Additionally, the panel recommended that the PUB moves towards a more integrated "risk-based" approach to better forecast the weather, said panel chairman Chan Eng Soon.

Based on additional analysis done with the Meteorological Services, the panel noted some clear trends in recent decades: Higher rainfall intensity and increased frequency of intense rains - consistent with the Intergovernmental Panel on Climate Change's findings, said Professor Chan.

The panel reiterated that the PUB has advanced modelling capabilities and has already collected high quality data, but more could be done. For instance, the error margins could be in centimetres rather than in 10 to 50 cm.

With more accurate data, PUB will have a faster lead time to react and provide the public with better information, Prof Chan said.