SINGAPORE - Last year proved to be one of the hottest years on record in Singapore, with the annual mean temperature hitting 28.4 deg C. A mean temperature of 27.94 deg C from 2010 to 2019 also made it the hottest decade ever.
In its 2019 review of Singapore's weather and climate released on Thursday (Jan 16), the Meteorological Service Singapore (MSS) said last year's mean temperature was the same as 2016's, which was 0.9 deg C higher than the 1981 to 2010 long-term average.
Last year's temperature record was likely the result of a combination of global warming and the occurrence of a coupled ocean-atmosphere phenomenon called the Indian Ocean Dipole (IOD), which developed in the Indian Ocean and caused drier, warmer conditions in South-east Asia.
In its positive phase, the IOD draws rainfall away from countries on the Indian Ocean's eastern rim, including Singapore and Australia, and causes warmer temperatures in affected areas.
“The cause of the warm temperatures in 2019 can be attributed to the strong positive IOD phase on top of the long-term warming trend over Singapore that is due to global warming and urbanisation,” the MSS told The Straits Times.
The MSS report follows a United Nations' warning of extreme weather events in 2020 and beyond as the decade ending last year recorded the highest global temperature and proved the hottest in history.
The mean temperature from 2010 to 2019 in Singapore surpassed that of the previous warmest decade from 2009 to 2018, which had a mean temperature of 27.89 deg C.
The MSS said this trend is consistent with global temperature patterns.
For example, the Copernicus Climate Change Service - the European Union's climate monitoring service - said on Jan 8 that 2019 was the second-hottest year on record.
Worldwide temperatures were only 0.04 deg C lower than in 2016, the warmest year on record.
Scientists say human activities such as the burning of fossil fuels and deforestation are emitting heat-trapping gases such as carbon dioxide into the air.
Data from the Scripps Institution of Oceanography in the United States showed that the current carbon dioxide concentration level stands at 413.2 parts per million (ppm) - a jump from the 280ppm recorded at the dawn of the Industrial Revolution.
The ever-thickening blanket of carbon dioxide and other greenhouse gases traps heat on Earth, causing global temperatures to spike and weather patterns to change, and increasing the frequency of extreme weather events around the world.
IOD and El Nino
Singapore is situated between the Indian and Pacific Oceans, and can be affected by changes in sea surface temperatures and atmospheric pressure in both basins.
Last year, the Republic was affected by such changes, as the positive phase of the IOD had developed. It resulted in drier-than-usual weather here.
The MSS said last year was the third-driest year recorded since 1869 - which consequently led to warmer conditions over Singapore and the nearby region.
"The year 2019 saw the development of one of the strongest, positive IOD events since the 1960s... The development of this event since the middle of 2019 contributed significantly to the below-average rainfall and higher temperatures observed, especially during the third quarter," it added.
An MSS spokesman explained that the lack of rainfall contributes to warmer temperatures, as drier conditions imply the suppression or lack of cloud formation.
“This in turn, allows for stronger heating of the ground and increase the surface temperatures,” she said.
Above-average temperatures were recorded in all months of 2019, with August (29.1 deg C) and September (29.0 deg C) breaking the record for the warmest August and September respectively, said the MSS.
As the development of the positive phase of the IOD over Singapore coincided with the south-west monsoon season, which brings drier-than-usual conditions here, it caused an escalation of the forest fires in the region, said the MSS.
Singapore experienced haze as a result, with the 24-hour Pollutant Standards Index (PSI) - a measure of air quality here - peaking at an unhealthy 154 in southern Singapore on Sept 19, the highest recorded for the year.
This positive phase of the IOD has now ended, MSS said.
The year 2016 also saw the occurrence of a coupled ocean-atmospheric phenomenon, but in a different ocean basin - the Pacific Ocean, located to Singapore's east.
That year, a strong El Nino event which started in 2015 led to drier weather across the region and caused temperatures to spike.
In 2015, transboundary haze from peatland fires in Indonesia were the region's worst on record.
Scientists predict that El Nino events could become more extreme as the world warms.
Drier, hotter but also wetter
Singapore had some respite from the haze with the arrival of rain late last year.
As it turned out, the usually rainy phase of the north-east monsoon season also broke a record.
The MSS noted that the Republic had experienced its longest north-east monsoon surge over the past decade.
Rain showers fell consistently for about seven days in December.
Said the MSS: "In the first half of December, Singapore experienced an extended period of cool, cloudy and windy conditions.
"Between Dec 9 and 15, a north-east monsoon surge brought periods of rain and showers over many parts of the island and were heavy on some occasions."
It brought about sweater weather in Singapore.
The lowest daily minimum temperature during the period was 22.0 deg C on Dec 11, said the MSS.
The daily maximum temperature during the monsoon surge episode ranged between 26.5 deg C and 29.9 deg C on almost all days, it added.
Other notable weather events last year included the occurrence of Singapore's first recorded landspout at Gul Way in south-western Singapore on Sept 27.
A landspout is a rotating column of air over land that stretches vertically to a developing cumulonimbus cloud (a type of cloud that usually brings rain) over it.
The development of intense thunderstorm clouds over the Tuas area also generated a rotating column of strong winds at Gul Way that lasted for several minutes, said the MSS.