SINGAPORE: If you thought that the weather has been unusually brisk over the past month, you would be correct. Singapore experienced the second coolest June in 20 years and the wettest in 10.
It ends a record 28 months of above-average monthly temperatures since February 2018, said the National Environment Agency’s (NEA) Meteorological Service Singapore (MSS).
The MSS said in its fortnightly weather outlook on Jul 1 that total rainfall for June was 233.8mm, higher than the previous high of 213mm recorded in June 2011.
The MSS also reported a monthly mean temperature of 28.1 degrees Celsius, 0.2 degrees Celsius cooler than the long-term June average.
June marks the start of the Southwest Monsoon season and the month tends to have short showers or thunderstorms in the afternoon and occasional Sumatra Squalls - a line of thunderstorms moving east across Singapore - just before dawn and midday, according to the MSS website.
This is part of a trend in which Singapore's annual rainfall total has been increasing by 97mm per decade on average since 1980. Heavy rainfalls have also become more common over the past few decades.
However, currently available research information cannot “definitively attribute” this trend to global warming, natural climate variability or other effects including urbanisation, said MSS on its website.
While Singapore's temperatures have been warming since 1972, MSS' report attributes the cool weather last month to the rain.
LA NINA PHENOMENON
Meanwhile, weather experts were mixed on the reasons for June's unusual weather.
Dr Matthias Roth, a professor of urban climatology at the National University of Singapore, said that the weather is part of “natural variability”.
Afternoon showers caused by strong solar heating at Earth’s surface, occasional early morning Sumatra Squalls and converging regional winds that destabilise the atmosphere and produce rainfall have all contributed to the rainfall in June, he said. More rain means more cloud cover, which reduces local air temperature.
Wet and cool weather will likely continue into July, he added, with a higher possibility of flash floods.
Assoc Prof Koh Tieh-Yong, a weather scientist at the Singapore University of Social Sciences, said that from May this year, the central tropical Pacific Ocean developed a low sea surface temperature anomaly. Higher surface pressure there causes converging winds here that bring more moisture which falls as rain.
The central Pacific cooling is likely to culminate in the La Nina phenomenon later this year, which would bring more rain and lower surface temperatures in Southeast Asia, he said.
However, climate scientist Benjamin Horton, director of the Earth Observatory of Singapore, believes that climate change contributed to the wetter and cooler weather in June and July.
Noting the increasing rainfall since the 1980s, Prof Horton explained that as the atmosphere gets warmer, it can hold more moisture. He added that with more moisture in the air, more rain follows. And the intensity of rainfall is partly dependent on how much water the air can hold at any given time.
Warming temperatures also increases the rate of evaporation from the oceans, he said.
“Think about heating a large pot of water on your stove - the higher you turn the dial, the faster the water evaporates,” he said, which contributes to more extreme rain.
He said: “It is clear why this is happening - global warming arising from the burning of fossil fuels. We have changed our atmosphere and oceans and we are already seeing the consequences.”
Editor’s note: An earlier version of this story said June 2020 was the coolest June in 20 years. This was based on a statement by the National Environment Agency, which has since issued a correction - June 2020 is the second coolest June in 20 years.