BRACE yourselves for more wet weather.
Heavy rain may hit Singapore from as early as today and last until Sunday, the result of two weather systems in the area, the National Environment Agency (NEA) said yesterday.
But the grim weather forecast does not necessarily mean that there will be more flooding, the agency said.
A moderate Sumatra squall - which develops at night over Sumatra or the Malacca Straits - may bring thunderstorms and heavy rain, lasting from one to two hours, either today or tomorrow morning.
A typical squall is accompanied by gusty winds of between 40kmh and 80kmh. Occasionally, such gusts are strong enough to uproot trees.
Separately, the effects of tropical storm Chanthu hitting southern China today may also result in short showers with thunder from late morning and this afternoon to Sunday.
Singapore is not directly affected by tropical storms - but they do influence local weather patterns, bringing more rain or unstable weather due to winds converging in the area.
For example, the June 16 flooding of Orchard Road was caused by such a convergence of winds.
Last Saturday's heavy rain, with 194mm recorded in the eastern part of Singapore, could be traced to typhoon Conson moving over China's Hainan Island.
Much of the current weather in the region can be attributed to the La Nina effect.
Unlike the El Nino weather phenomenon - which spells hot, dry weather - La Nina is associated with wetter weather as it exacerbates storms, droughts and cyclones.
Typically, Singapore's wettest month is December when the north-east monsoon brings spells of heavy rain that can last for up to a week at a time. They can be caused by wind 'surges' originating from as far away as Siberia.
Such surges, caused by a pressure difference between freezing Central Asia and the warmer tropics, mean north-east monsoon winds blowing across the South China Sea pick up plenty of moisture, which is deposited as rain in the tropics.
More than half the yearly rainfall here comes in the second half of the year.
To keep the public informed about the weather, there are updates on Weather@SG, which can be accessed online and via mobile phones at http://weather.nea.gov.sg
The forecast is updated every five minutes and is shown as a colour-coded graphic layered over Singapore, which allows people to zoom in to town level and check for rain.
It also issues heavy-rain warnings and features three-hour, 12-hour and three-day forecasts, rain locations over Singapore as well as temperature and humidity information.
This information is also available at the NEA website at http://www.nea.gov.sg, Twitter at http://twitter.com/neasg and via the hotline 6542-7788.
Additional reporting by Amresh Gunasingham
100mm: Expect floods if this much rain falls in an hour
Victoria Vaughan Straits Times 22 Jul 10;
IF MORE than 100mm of rain falls in an hour, expect flooding.
National water agency PUB said yesterday that in the last 10 occasions when rain of that intensity fell, it had resulted in floods eight times.
Of those past 10 rainstorms, two happened last year, three the year before, two in 2007 and three in 2006.
Every year, Singapore gets, on average, two storms dumping that much rain in an hour, and nine storms in which the 100mm is spread over three hours.
PUB, responding to questions from reporters after the recent floods, explained that besides the intensity of a storm, the following factors also work together to set up perfect conditions for flooding:
# The type of developments in the area; that is, whether it is built up.
# The kind of surfaces there; that is, whether they are paved or porous.
# The distribution and movement of the rainfall.
# The ground level in relation to the water levels in the drains.
# The capacity of the drains to channel away the storm water.
# Whether there is a blockage in the drains.
Of the last 10 most intense rainstorms here, the heaviest happened on July 19, 2007. The monitoring station at the Ulu Pandan water treatment plant recorded 137mm in an hour that day, said the National Environment Agency (NEA).
The recent downpours have not topped that. The June 16 storm which put Orchard Road under water sent down 101.6mm in two hours.
Orchard Road was not even the wettest place that day: Sentosa logged 115mm of rain.
Another recent storm, that on July 17 from Typhoon Conson, brought 114mm of rain to the Lower Peirce Reservoir in one hour.
But a high of 194mm that day was recorded at Poole Road in Tanjong Katong.
The second heaviest of the last 10 intense rainstorms came on April 3, 2008, when 126mm was dumped on Jurong Pier Road. This burst led to flash floods in Dunearn Road near Swiss Club Road, Upper Paya Lebar Road near Bartley Road and Commonwealth Avenue. The storm lasted from 4.20pm to 6pm.
The third heaviest downpour happened on Nov 19 last year, when 121mm was recorded at the Ngee Ann Polytechnic station. The Bukit Timah canal burst its banks and knee-deep water brought traffic to a standstill along several stretches of Bukit Timah - Coronation Road to Third Avenue, Wilby Road to Blackmore Drive and the Sixth Avenue junction.
The downpour took place between 12.50pm and 3.20pm.
From the history books, Dec 2, 1978, still holds the record for the highest amount of rainfall in a day in the last 60 years. That day, 512 mm fell.
Seven people died, including five who drowned, and about 1,000 people were rescued and evacuated by the Singapore Armed Forces and the police in one of the biggest rescue and evacuation operations here, according to the Defence Ministry website.
The highest one-hour rainfall, at 148mm, was recorded on Nov 2, 1995.
What will be done to improve drainage
Straits Times 22 Jul 10;
STEPS are being taken to address the shortcomings of the drainage system in seven areas hit by the recent floods.
Singapore's water agency PUB said work will include raising roads as well as widening and deepening drains; where possible, the works will be expedited.
# Jalan Besar and Little India: Work on the Kelantan Road outlet drain will start by year's end; tenders will be called then for works to improve the drains in Syed Alwi Road.
# Bedok and Telok Kurau: Three low-lying roads in these areas will be raised - Bedok Garden, Bedok Lane and Lorong G Telok Kurau.
# Bukit Timah Canal: Tenders for improvement works will be called this month for the stretch between Wilby Road and Maple Avenue. Next year, tenders will be called to improve the canal at Dunearn Road near Swiss Club Link. Balmoral Road, near its junction with Bukit Timah Road, will be raised.
# Farrer Park, Newton, Kampung Java and Novena: Tenders for improvements to Rochor Canal between Jalan Besar and Crawford Street are expected to be called in October or November. Work by the Land Transport Authority has begun on the canal between Java Road and Jalan Besar. Improvements are also being made to the drains along Thomson Road from Moulmein Road to Bukit Timah Canal and Norfolk Road.
# Jalan Haji Alias: The work to widen and deepen the upstream stretch of the Jalan Haji Alias outlet drain at Sixth Avenue to Coronation Road West is expected to be done by February.
# Paya Lebar and MacPherson: Tenders will be out by year's end to improve the Happy Avenue outlet drain. At Siang Kuang Avenue, improvements to the MacPherson Road outlet drain are under way. At the AZ Building and Cisco Building, tenders to upgrade the downstream stretch of Geylang River from Dunman Road to Guillemard Road closed last month. Work is expected to begin by October.
# Jurong: The upgrading of the drain along Enterprise Road is expected to be completed by year's end.
PUB also announced yesterday its other plans to alleviate flooding:
# Sensors: It will make the data from its 32 water-level sensors public through its website by early next month.
It will also increase the number of these sensors to 90 by the end of the year so that all major waterways, flood-prone areas and hot spots will have them.
Those with property near such sensors have been invited to subscribe to SMS alerts, which they will receive when the water hits certain levels.
# Warning system: PUB and the National Environment Agency are looking into an integrated system which can give the public earlier warning of heavy rain and rising water levels in canals. This will be completed in the next few months.
VICTORIA VAUGHAN
More wet weather in Singapore for the week: NEA
Imelda Saad Channel NewsAsia 21 Jul 10;
SINGAPORE : Expect more wet weather in Singapore for the rest of the week.
The National Environment Agency (NEA) said Tropical Storm Chanthu is expected to make landfall in Southern China on Thursday.
This may bring wet conditions to the region, including Singapore.
Short duration showers with thunder are expected, mostly between the late morning and afternoon.
A moderate Sumatra squall is also likely to affect Singapore either on Thursday or Friday morning.
NEA said heavy rain warnings may not lead to floods.
There are many factors leading to floods, including rainfall intensity, flood water runoff, location and the capacity of drains.
Still, the public can be prepared.
The public can obtain the latest weather reports, including heavy rain warnings.
They can also tune in to radio broadcasts, call NEA's weather forecast hotline at 6542-7788, access the mobile weather service which is available at Weather@SG (weather.nea.gov.sg), or visit the NEA website at www.nea.gov.sg.
To alleviate the flooding problem, the PUB has installed more than 30 sensors in key canals to track water levels.
This information will be made available on PUB's website by early August.
The number of sensors will be increased to 90 by year's end to cover all major waterways and flood-prone areas.
An integrated early warning system will be completed within the next few months.
Drainage improvement works in flood-prone areas are also being brought forward.
Meanwhile, the authorities are working with businesses affected by the spate of recent floodings in Singapore.
Sandbags have been placed at these premises as a temporary measure, while building owners have been advised to look into installing permanent structure to alleviate flooding within their premises. - CNA /ls
More greenery, better drainage system
Esther Ng Today Online 22 Jul 10;
If global weather patterns bring more rain - and flooding occurs regularly - developers will need to relook the design of their developments, which could include building multi-storey car parks, architects told MediaCorp.
"It can be aesthetically pleasing with greenery and landscaping, blending in with communal areas," Singapore Institute of Architects president Ashvinkumar Kantilal said. But this is not always possible to build multi-storey carparks when there are height restrictions. Developers also need to look at the topography of the land, said architect Dean Zhou, 34. "At the moment there's too much 'hardscape'. There needs to be more green turf and spaces to absorb the water," he said.
Improving the drainage system and installing more pumps in a basement carpark are other options. Building a hump of 15cm above the minimum platform level before the entrance of a basement carpark would also help, Mr Ashvinkumar said. ESTHER NG