Women sit in the shade of an art installation set up at a park in Changwon, South Gyeongsang Province, April 28. Last month was South Korea's hottest April on record since it began keeping meteorological records more than 50 years ago. Yonhap

Last month was South Korea's hottest April on record in the more than 50 years it has been keeping meteorological records.

According to the Korea Meteorological Administration (KMA), Tuesday, the average temperature last month was 14.9 degrees Celsius, which was higher than the previous record of 14.7 degrees Celsius in 1998.

Compared with the average April temperature between 1991 and 2020, last month was 2.8 degrees warmer, the agency's analysis shows.

The average daily high that month was 21.1 degrees Celsius, 2.5 degrees higher than daily highs during the 30-year period.

April 14 was the hottest day, with temperatures hitting around 30 degrees Celsius in some areas of the capital region and Gangwon Province.

The KMA explained that the onset of the early heat wave can be attributed to multiple factors, with particular emphasis on the significant role of warm and humid southerly winds.

In April, the El Nino phenomenon, characterized by above-normal sea temperatures in the eastern and central Pacific Ocean, experienced a weakening effect.

"This led to a decrease in convective activity across the Western Pacific region and consequently strengthened a high-pressure front in the eastern Philippines region," said an official from the KMA.

"Warm southerly winds have consistently flowed toward Korea as an anticyclone is situated in the eastern Philippines. This is because the wind moves clockwise around along the edge of an anticyclone in the Northern Hemisphere."

Moreover, the absence of cold air descending from the Arctic into the mid-latitudes has exacerbated the heat, according to the KMA. This has resulted in a weaker-than-usual continental anticyclone system in April, allowing migratory anticyclones to pass through Korea frequently.

"The influence of this migratory anticyclone has caused surface temperatures to rise significantly under clear skies. Additionally, when this anticyclone is positioned to the east of Korea, it adds warm southeast winds with the heat, resulting in hot temperatures across the region," he said.

Korea is not the only country experiencing unusual heat. Other parts of the world, including Hong Kong and eastern India, have also reported their highest April temperatures on record.

Last month's average temperature in the Chinese special administrative region was 26.4 degrees Celsius, its hottest April recorded in 140 years of data collection.

Globally, scientists warn that extreme heat will become more frequent and intense because of human-caused climate change.

In addition to the abnormal heat, Korea also experienced heavy rain in early May. During the Children's Day long weekend, heavy rains swept across the southern regions of the country and Jeju Island, reaching levels typically seen during the monsoon season in mid-summer.

On Sunday, unprecedented rainfall was seen in Gwangyang and Jindo County in South Jeolla Province, with 198.6 millimeters and 112.8 millimeters, respectively, marking the highest single-day precipitation on record.

The downpour intensified from the afternoon of Sunday through Monday morning and started to ease on Monday afternoon. The KMA forecast that the rain would stop in most areas on Tuesday, but it would continue until Wednesday in Yeongdong County, Gangwon Province.

"The heavy rainfall earlier this week was attributed to the convergence of an anticyclone, which brings southerly winds to Korea and carries heat and abundant moisture, with a low-pressure system," the KMA official said.

In June, when the rainy season usually begins, Korea experiences southerly winds induced by the North Pacific high-pressure system. Currently, sea surface temperatures around the Korean Peninsula are 1 to 3 degrees Celsius above average, which can be a reason for the moisture-laden southern winds.

"There is a likelihood of heavy rainfall during this rainy season as a result of these conditions," he said.