A clear increase in the average annual temperature is observed worldwide, and climate changes take place in response to that increase. This affects not only the ecosystem, but also to mankind. Of all those aspects of climate change, people are especially interested in the length of each season, and people acknowledge that the duration of spring and fall has been shortened over the past several years. Still, it is difficult to observe this kind of phenomenon with the simple analysis of dividing the seasons and calculating the duration. Therefore, this study attempted to set up a more intuitive standard which well reflects the current situation. This study also divided the daily climate into 4 states using the daily maximum and minimum temperature. Moreover, using the
Hidden Markov Model, this study calculated the duration of each season and analyzed its tendency based on the daily temperature data of the last 53 years (1960~2012). According to the result, the duration of spring and fall showed mild decreasing tendency over the past 53 years, and the duration of fall decreased even more during the past 30 years in the Korean peninsula. After 1960, the start of spring was advanced, which decreased the length of winter for about 11 days. On the other hand, the duration of summer increased for about 25 days, which is consistent with the worldwide tendency of temperature increase.