The heavy downpour yesterday morning, which caused flash floods in the central and western parts of Singapore, was equal to half the average rainfall for the entire month of June.
PUB said about 85mm of rainfall was recorded between 9.30am and 11.30am. The average rainfall for June is 130.7mm. Areas which saw flooding included Lorong Kismis in Upper Bukit Timah, Dunearn Road and Bukit Timah.
At 10.11am, PUB tweeted that flash floods had been reported in Dunearn Road, from Yarwood Avenue to Binjai Park, affecting three lanes of the road. About an hour later, it tweeted that the flooding had eased.
Yesterday's floods were the latest in a series over the past month.
On Tuesday, more than a month's rainfall - about 150mm - fell in four hours in Old Toh Tuck Road, causing flash floods in the central and western parts of Singapore.
On May 26, Kramat Lane and Cavenagh Road, along Orchard Road, saw water rising up to mid-tyre level for about 10 minutes.
PUB said the overall rainfall for June is likely to be above average for most of Singapore. It urged people to exercise caution and avoid walking or driving in flooded areas.
We are moving into the supposed drier months - in Singapore the wetter months would be February and December - so heavy rainfall is quite unusual in June.
PROFESSOR BENJAMIN HORTON, chair of the Asian School of the Environment at Nanyang Technological University.
Professor Benjamin Horton, chair of the Asian School of the Environment at Nanyang Technological University, said that it was unusual to see such heavy rainfall in June.
June is the onset of the south-west monsoon season, which usually lasts until September and is characterised by relatively drier and warmer weather conditions.
"We are moving into the supposed drier months - in Singapore the wetter months would be February and December - so heavy rainfall is quite unusual in June," said Prof Horton.
He said that while a single event could not be attributed to climate change, one prediction of climate change is heavy precipitation from more moisture in the atmosphere.
The Meteorological Service Singapore said on June 14 that monsoon conditions are expected to extend into September. It said short-duration thundery showers were expected on five to seven days in the second half of June, mostly in the late morning and afternoon.
PUB said it has ongoing drainage upgrading works at the Bukit Timah First Diversion Canal to increase its capacity. "When completed in the first quarter of 2019, flooding risk in the Bukit Timah area would be alleviated," it added. It will protect buildings in the catchment area such as Ngee Ann Polytechnic, Beauty World Plaza, Bukit Timah Shopping Centre and Sime Darby Centre.
Upgrading works for the Stamford Detention Tank and Stamford Diversion Canal are ongoing, and are expected to be completed by the third quarter of this year.
These are two major projects being built to protect Orchard Road, which was hit by a series of flash floods between 2010 and 2012.
The diversion canal will relieve Stamford Canal of a portion of water, while the detention tank will hold water temporarily so less water flows into Stamford Canal during heavy rain.