2021 was Singapore's second-wettest year since 1980, with 33% more rain than average: Met Service

SINGAPORE — Singaporeans who thought 2021 was unusually wet were not mistaken. It was the country's second-wettest year since 1980, with yearly total rainfall at the Changi climate station 33 per cent above the long-term average. 

And in January 2021, rainfall was the highest in more than 100 years.

Although the wetter conditions resulted in several notable weather events, such as an unseasonably wet August, the Meteorological Service Singapore (MSS) said that it also contributed to moderating the island’s overall temperature.

MSS released these findings on Friday (Jan 28) in its yearly weather review, which also recorded the period of 2012 to 2021 as Singapore’s warmest decade.

HIGHER-THAN-AVERAGE RAINFALL

Most months last year saw above-average rainfall.

This led to a yearly total rainfall record of 2,809.6mm at the Changi climate station, which was 33 per cent higher than its long-term average of 2,113.3mm. 

When averaged across Singapore’s 32 climate stations, the yearly total rainfall was 3,167.7mm — 25 per cent higher than the long-term yearly average of 2,534.4mm.

Based on the islandwide average, MSS said that almost all of these wetter months ranked within the top 10 wettest for the respective months over the past four decades.

Singapore experienced its wettest year in 2007. The total yearly rainfall recorded that year at the Changi climate station was 2,886.2mm. 

MSS previously told TODAY that it operates a dense network of stations as there could be variations in the rainfall across the island depending on each event. As such, it may be difficult to represent the average rainfall based on a single station.

Although there is variability in rainfall across the island, the trend of the year-to-year annual rainfall at all the stations islandwide is mostly similar.

“The Changi climate station, with its continuous long-term records, thus provides a good indication of Singapore rainfall trends,” the agency said.

WHAT CAUSED IT?

In explaining why 2021 was unusually wet, MSS said that it had to do with last year’s La Nina conditions and the presence of a negative Indian Ocean Dipole. Both are weather phenomena.

La Nina conditions and negative Indian Ocean Dipole events typically result in wetter-than-average conditions over Singapore and the nearby region, particularly during the southwest monsoon season.

La Nina conditions prevailed in the first quarter of 2021, before it returned to its neutral El Nino conditions in the second quarter of last year.

About four months later, these La Nina conditions re-emerged towards the end of the third quarter.

During this quarter, MSS said that a negative Indian Ocean Dipole — a natural climate phenomenon influencing rainfall patterns around the Indian Ocean — was also established.

Its strength fluctuated considerably in the second half of the year and returned to neutral by the end of 2021.

WARMEST DECADE

Aside from the significantly above-average rainfall, MSS said that the last 10 years from 2012 to 2021 were the warmest on record, with a mean temperature of 27.97°C.

This is 0.02°C higher than the previous record of 27.95°C from 2010 to 2019.

The yearly mean temperature for 2021 was 27.9°C — 0.1°C above the long-term average of 27.8°C.

“This ranks 2021 as Singapore’s joint 10th-warmest year on record, along with 2018, 2014, 2009 and 2004,” MSS said.

In the first half of 2021, near-average temperatures were observed for the most part, while warmer-than-average conditions were observed in the second half of the year.

These warmer-than-average temperatures towards the end of the year were associated with relatively drier weather conditions, MSS added.

The mean temperature of 27.7°C for December 2021 was a joint record with December 2015 for the warmest December since temperature records started in 1929.

By contrast, MSS said that the cooler-than-average temperatures recorded in January and August 2021 were associated with significantly higher-than-average rainfall over those two months.

The mean temperature was 26°C in January 2021 and 27.6°C in August 2021, which are 0.8°C and 0.5°C cooler than their respective long-term monthly averages.

MSS also said that January 2021 was the coolest January in the past 30 years, while August 2021 was the second-coolest August in the past two decades.

NOTABLE WEATHER EVENTS

MSS also highlighted three months — January, February and August 2021 — that saw the occurrence of what it described as notable weather events. 

It said that “exceptionally wet and cool weather” was recorded in January 2021 due to a northeast monsoon surge that brought continuous widespread rain over Singapore in the first weekend of the year.

The highest daily total rainfall of 210.6mm was recorded at the Changi climate station on Jan 2, 2021.

A week later, another monsoon surge brought windy and rainy weather between Jan 8 and 13, 2021. The rain was heaviest on Jan 10, 2021.

MSS said that the monthly rainfall recorded at the Changi climate station for January 2021 was 692.8mm, with more than 90 per cent (648.4mm) recorded in the first fortnight alone.

This meant that January 2021 was the second-wettest January since rainfall records began in 1869, as it had exceeded the previous second-highest value of 634.5mm recorded in 1918.

In contrast, February 2021 turned out to be “very dry and windy”. The highest daily total rainfall was just 46.9mm at Jurong West on Feb 11, while the Changi climate station recorded a mere 1mm for the entire month.

February 2021 was the second-driest after February 2014, which saw just 0.2mm of rainfall.

February 2021 was also the second windiest since continuous wind records started in 1984. The Changi climate station recorded an average daily wind speed of 13.1kmh, just behind the 13.7kmh recorded in February 2014.

While August is typically one of the drier months of the year, MSS said that there was “well-above average” rainfall islandwide in August 2021, with the Changi climate station recording nearly twice its long-term monthly average.

There were two days with exceptionally heavy rain that resulted in flash floods in some areas.

Several spells of moderate to heavy thundery showers in the pre-dawn hours and morning led to flash floods in areas such as the junction of Tampines Avenue 10 and Pasir Ris Drive 12 on Aug 20, 2021 and Bukit Timah on Aug 24, 2021.

MSS said that Aug 24 was the wettest day of last year. A “remarkable daily total rainfall” of 247.2mm was recorded at the Mandai station, setting a record for the highest daily total rainfall for the month of August.

It added that this far surpassed the previous high of 181.8mm at Changi on Aug 22, 1983.