Reasons for dry spell run hot and cold

SINGAPORE - Singapore and Malaysia's prolonged dry weather may have been caused by cooler-than-usual sea surface temperatures in the nearby South China Sea.

This could have lessened the evaporation of seawater and the moisture content of monsoonal winds which help cause rain here, and possibly weakened the force of the winds themselves.

Other factors could include abnormal weather events in other parts of the world, such as extreme cold and warmth in the United States, having a "knock-on" impact on regional weather.

Global warming may also have increased the odds of extreme weather events worldwide, such as the current heatwave and drought in Australia.

Weather researchers laid out these possibilities to The Straits Times on Wednesday, but stressed that more research would be needed to substantiate them and clarify their effects.

National University of Singapore weather researcher Winston Chow added that while these factors may have prolonged and worsened the lack of rain, dry spells are common at this time of year in Singapore and Malaysia, in the dry phase of the monsoon season.

"What is not normal is the duration of the dry spell... but picking a single reason is extremely difficult without 'attributional' studies, and these have to be done after the event," said Dr Chow, an assistant professor in the Department of Geography.

Barely any rain fell in Singapore for 27 consecutive days from Jan 13 to Feb 8.

The lack of rain has also persisted since then, despite brief showers on a few days.

Much of Malaysia has also been bone-dry for a month, prompting authorities to start rationing water in Selangor, the country's most populous state, from today.

Australia had its hottest year on record last year. The heatwave has continued into this year, with Prime Minister Tony Abbott announcing a A$320million (S$365 million) package for stricken farmers this week.

In Indonesia, unusually dry weather has also resulted in more forest fires and haze. The air pollutant index in Dumai, about 270km north-west of Singapore in the Riau province of Sumatra, hit a hazardous 776 on Tuesday, but Singapore's index showed air quality here remains "good".

Dr Chow said rain is likely to return to Singapore in the middle of next month due to favourable weather conditions expected then.

A phenomenon known as the inter-tropical convergence zone is expected to force moist air upwards, resulting in rain.

The National Environment Agency had estimated that the dry spell would "persist into the first half of March".

But the agency also warned that climate change "increases the risk of both wetter and drier extremes", although more studies are needed to investigate exactly how Singapore would be affected.

While it could not pinpoint the cause of changes in patterns, it noted there have been more frequent and intense rains over the past few decades. The maximum rainfall in an hour, for example, increased from 80mm in 1980 to 107mm in 2012.

In Australia, the former executive director of the Australian National University's Climate Change Institute, Professor Will Steffen, co-authored a report released last month outlining how Australia's heatwaves have become hotter and longer.

"Climate change is loading the dice towards more extreme hot weather," he told reporters.

zengkun@sph.com.sg

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