Jung Da-hyun is a reporter at The Korea Times, covering social issues in Korea, including foreign residents, education, environment and politics. Driven by a deep interest in people’s stories, she focuses on investigative and feature reporting through direct interviews and field coverage. She received the Amnesty International Korea Media Award for her “Deepfake Crisis at Schools” series. Reach her at dahyun08@koreatimes.co.kr. Always open to hearing your stories.
Korea's summers are getting longer and hotter, data shows
Heat haze shimmers above a road in Ulsan amid scorching summer temperatures, Thursday. Yonhap
By Jung Da-hyun
Heat wave season now arrive a month earlier than in 1970s
Korea's summers are becoming longer and more intense as heat waves arrive earlier, persist longer, with tropical nights growing increasingly common.
A new analysis released by the Korea Meteorological Administration (KMA), Friday, compared heat wave and tropical night patterns from 2016 to 2025 with those recorded from 1973 to 1982. It found that heat waves now begin 10 to 30 days earlier nationwide and end about 10 days later than five decades ago.
A heat wave is defined as a day with a high of at least 33 degrees Celsius, while a tropical night refers to one in which temperatures stay above 25 degrees overnight.
In Gangneung and parts of the Yeongnam region, including Daegu, Hapcheon, Miryang, Yeongdeok and Pohang, where heat waves tend to arrive earlier than in other parts of the country, the onset of heat waves has shifted to early June over the past decade, more than 10 days earlier than during the 1973 to 1982 period, when they typically began in mid- to late June.
A similar shift has been seen across inland central regions, including Seoul, Icheon, Chuncheon and Cheongju, where heat waves now typically begin in June instead of early to mid-July.
In Seoul, for example, the average heat wave onset moved from July 19 to June 24.
Heat waves are also lasting longer nationwide. Over the past decade, they have typically persisted until late August, about 10 days later than during the 1973 to 1982 period, when they generally ended in mid-August.
Tropical nights have also started earlier and lasted longer. Nationwide, they now typically begin in early to mid-July, five to 15 days earlier than in the past, and persist into early September instead of ending in late August. Along the southern coast and on Jeju Island, they have typically continued until early September over the past decade.
The data also found that both heat waves and tropical nights have become steadily more frequent over the past 53 years.
Since 1973, the number of heat wave days has increased by an average of 1.8 days every decade, while tropical nights have increased by 1.6 days per decade nationwide.
The average heat wave season has more than doubled, from 8.3 days during the 1973 to 1982 period to 18.3 days over the past decade.
The average number of tropical nights has nearly tripled, rising from 4.1 days to 12.2 days.
The KMA said the trend is largely the result of changes in the North Pacific High, the dominant weather system that shapes Korea’s summer climate.
As the North Pacific High expands toward the Korean Peninsula, it draws in hot, humid air and brings clear skies that intensify solar heating, prolonging periods of extreme heat. Over the past decade, the system has increasingly expanded northwestward from June and settled south of the peninsula.
The KMA added that warmer surrounding seas have also contributed to the longer tropical night season by preventing nighttime temperatures from cooling.
Meanwhile, the ongoing monsoon season is expected to end early next week and be followed by an intense heat wave.