Tuesday, June 7, 2011

Hard to tell if the weather is changing, say experts

Jun 7, 2011

But what has happened fits expected pattern of a warming climate
By Grace Chua

IS SINGAPORE'S weather changing?

On Sunday, speaking after the year's worst floods, Environment and Water Resources Minister Vivian Balakrishnan said there was a 'very high probability that our weather patterns have changed'.

While experts say it is too early to tell if the weather is changing, they add that what has happened fits the pattern of a warming climate.

Associate Professor Matthias Roth, deputy head of the National University of Singapore's geography department, explained: 'We cannot link one particular weather phenomenon to climate or climate change, because the latter is a long-term average of the weather, which is experienced on a day-to-day basis.'

One heavy thunderstorm will not change the long-term average - but enough of them will, he said. So more data has to be collected over the years before there is enough evidence that the climate is shifting.

'Having said this, the recently observed pattern fits the expected increase in extreme events predicted to occur in a warming climate,' he added.

The National Environment Agency (NEA), which provides meteorological services, said it is studying the impact of climate change on local weather.

Already, the first phase of Singapore's climate change vulnerability study, released last year, has predicted that the temperature could rise between 2.7 deg C and 4.4 deg C from the present average of 26.8 deg C by 2100.

But it showed no discernible trend in rainfall patterns over the next century.

Scientists at the Singapore-MIT Alliance for Research & Technology's Centre for Environmental Sensing and Modelling have suggested mechanisms by which human activity could change monsoons.

For example, fine particles of black carbon or soot from burning fuel could absorb heat, warming the air, drawing moisture in and hastening and intensifying the monsoon, said MIT senior research scientist, Dr Chien Wang.

The NEA attributed Sunday's thunderstorm to the convergence of winds which brought unstable weather conditions and rain clouds over Singapore and the surrounding region.

The region is entering the south-west monsoon season, which typically lasts from June to September, and the onset of which is determined by the direction of prevailing winds.

On Sunday, rain clouds developed to the south-east and moved towards Singapore, Batam and the southern part of Johor.

'As the convergence of winds occurred close to Singapore, the rainfall over Singapore was particularly intense as compared to the nearby states,' an NEA spokesman said.

The heaviest downpour, over the central area, added up to 124mm, or about 77 per cent of the average monthly rainfall for June.

About 65mm of rain fell in just half an hour, which made the rainfall more intense than last June, when 100mm of rain fell in two hours and Orchard Road was flooded.

Sunday's thunderstorm was also different in origin from the storm on June 1, which followed hot weather and was caused by strong convective heating over land. A teenage boy was swept away by flood waters and drowned that day after he fell into a swollen drain.

But is it possible to predict such fierce thunderstorms?

That is difficult, said Prof Roth, especially in the tropics.

In temperate zones, the weather is associated with predictable low or high-pressure systems.

But in the tropics, rainfall is associated with the rising of hot air, a phenomenon 'which can appear at any time if the conditions are right', he said.

According to the NEA website, south- west monsoon conditions will prevail over Singapore and the surrounding region until June 15, with surface winds from the south and south-east.

And for the next three days, showers with thunder are expected over north, east and central Singapore: This afternoon, tomorrow morning and early afternoon, and on Thursday morning.


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