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Improved seasonal definition and projected future seasons in South Korea

Seasons are fundamental climatological phenomena, and their changes have significantly affected the sustainability of nature and human society. Suitable criteria to define the seasonal indicators of start date and length of seasons are required for the timely planning of socio‐economic activities. However, unsuitable cases of seasonal indicators have been identified in the seasonal definition used by Korea Meteorological Administration (KMA). We devised the data processing method to calculate three seasonal indicators: start date, length, and abnormal days of seasons. The past (1921–2010) and future (2021–2100) climate data of daily mean temperature were used in estimating the three seasonal indicators; they were obtained from the weather stations in South Korea and under the Representative Concentration Pathway (RCP) scenarios, respectively. The modified definitions with the moving averages of 15‐, 31‐, 45‐, 61‐, and 91‐day improved in estimating the start date and length of seasons compared with the current KMA definition. Additionally, abnormal days of seasons in the modified definitions were found to reduce significantly. Under the RCP8.5 scenario, the earlier advance of spring and summer by 4.9 and 3.9 days per decade, respectively, and the delayed autumn and winter by 3.2 and 2.0 days per decade, respectively, were expected over the 21st century. Correspondingly, the extended summer and the shortened winter by 7.1 days per decade and 5.1 days per decade were projected, respectively. The estimated future changes in seasons using the improved seasonal definition can be used for socio‐economic sectors and the general public to adapt to a warmer climate.