South Korea's spring was second hottest on record, with earliest-ever heat waves in May

South Korea recorded its second-highest spring average temperature since modern weather observations began, with an unusually early heat wave striking parts of the country in May, the Korea Meteorological Administration said Tuesday.

The national average temperature this spring reached 13.3 degrees Celsius, the weather agency said — 1.4 degrees above the long-term normal of 11.9 degrees and 0.8 degrees above last year's 12.5 degrees. Among the 54 springs recorded since 1973, when the national observation network was significantly expanded, it ranked second warmest. The all-time high remains 2023, at 13.5 degrees.

Seven of the past 10 years (2017–2026) now rank among the 10 warmest springs on record, pointing to a clear upward trend in spring temperatures.

Abnormally high temperatures recurred throughout the season, clustering in late March, mid-April and mid-May. Seoul's daytime high reached 29.4 degrees on April 19. On May 17 and 18, daily maximum temperature records for mid-May were broken at 22 stations nationwide, including Wonju, Chungju, Gwangju, Andong and Daegu.

The national average temperature for mid-May hit 19.7 degrees, the highest ever recorded for that period. Gumi in North Gyeongsang Province logged its earliest heat wave on record on May 16; Geochang in South Gyeongsang Province followed on May 17; and Mungyeong, Andong and Yeongcheon, all in North Gyeongsang Province, did the same on May 18. The nationwide heat wave day count for May stood at 0.5 days, the second highest on record for the month.

The weather agency attributed the extreme heat to a strengthening of mid-latitude atmospheric waves driven by the North Atlantic Oscillation, which caused an intense high-pressure circulation to develop over the Korean Peninsula.

Rainfall this spring was close to normal. Total precipitation nationwide came to 268.1 millimeters, or 108.2 percent of the long-term average of 248.4 millimeters, and 36.5 millimeters more than last year's 231.6 millimeters.

The distribution was uneven across the season, however. Rain fell roughly every other day in early April, while in May, a low-pressure system brought heavy rainfall concentrated nationwide on May 20 and 21.

Particularly heavy rain — ranging from around 100 to 200 millimeters — fell along the Yeongdong coast of Gangwon Province, the South Jeolla Province coastline and the Gyeongsang region. Daily precipitation records for mid-May were broken at Gunsan, Jeonju, Yeosu, Namhae, Daegu and Yeongdeok.

Spring meteorological drought expanded across central regions of the country but was largely resolved by nationwide rainfall in late May.

Sea surface temperatures were also elevated. The average sea surface temperature in waters surrounding South Korea this spring reached 14.0 degrees, the second highest in the past decade and 1.6 degrees above last year's level. The East Sea recorded the largest increase among individual sea areas, rising 2.4 degrees from last year.

"This spring, an early heat spell arrived from mid-April, and some areas experienced their earliest heat waves on record in May — weather that made the ongoing warming trend in spring temperatures unmistakably felt," Korea Meteorological Administration Commissioner Lee Mi-seon said. "We will closely monitor abnormal climate events and work in close cooperation with disaster prevention agencies to do our utmost in responding to natural disasters."