Long term change of interannual variation in East Asian summer precipitation since 1999

Abstract

Summer precipitation in East Asia, known as the Meiyu in China, the Baiu in Japan, and the Changma in Korea, is a vital source of fresh water. It has been widely studied how this complex system has fluctuated in its duration, intensity, and spatial distribution as well as frequency of extreme events associated with these changes. Changing mechanisms of such changes can be attributed to several factors: anthropogenically induced warming and natural climate variabilities including El Niño-Southern Oscillation (ENSO) and others. This study found that the interannual variation of East Asian summer precipitation experienced an interdecadal shift. We applied the Self-Organizing Map (SOM) on the satellite-merged precipitation dataset – Global Precipitation Climatology Project (GPCP) data for the period of 1979 – 2022 and found that the mean July-August precipitation patterns in East Asia have changed. The elongated rainband dominated in the period of 1979-1998 transitioned to a more regional pattern over northern China and the northern Korean peninsula in the latter decades. In the previous period, the Okhotsk Sea and tropical monsoon air masses played a significant role in the formation of the precipitation pattern. However, in the latter period, along with the Okhotsk Sea air masses, especially the North Pacific air masses played an important role. The role of the Western North Pacific Subtropical High (WNPSH) in this changing precipitation pattern was also analyzed. The westward extension and strengthening of the WNPSH collapsed the triple precipitation pattern that existed over the tropical oceans and the East China Sea, and influenced precipitation in Northeast Asia beyond the MBC domain. This study offers new insights into East Asian monsoon precipitation changes by employing a different analytical approach to clustering over the years. Although it relies on observational data and does not account for the intraseasonal variability of monsoon rainfall or use climate models to isolate specific conditions, it contributes new perspectives to the existing body of research.