Centennial-scale dry-wet variations in East Asia

摘要

This study attempts to combine four independent long-term climatic data and modern observations into one cohesive set; to describe the spatial and temporal patterns of variability of dry and wet periods in East Asia over the past one thousand years; and to examine physical causes of the pattern variations. The data include the 220-year observed precipitation in Seoul, South Korea, the dryness-wetness intensity data in eastern China for the last 530 years, and other two independent chronologies of dryness-wetness grades in the past millennium in eastern China based on instrumental observations and historical documents. Various analysis methods including wavelet transform and rotated empirical orthogonal function were used in revealing climate variations from these datasets. Major results show that the dry and wet anomalies initially appeared in the north part of eastern China and then migrated southward to affect south China. This process is repeated about every 70 years. However, in contrast in the last two decades of the twentieth century a dry situation appeared in north China and a wet climate predominated in the south part of the country. The multidecadal variations of the monsoon circulation in East Asia and the thermal contrast between inland Asia and its surrounding oceans may contribute to the dry-wet phase alternation or the migration of dry-wet anomalies. In regional scale variations, a consistent dry or wet pattern was observed spreading from the lower Yangtze River valley to South Korea. Frequencies of severe dry-wet situations were low in the eighteenth and nineteenth century and they were higher in the twentieth century. The recent increasing trend in frequencies of severe dry-wet chances occurred along with global warming and regional climatic changes in China.