Observed short- and long-term changes in summer precipitation over South Korea and their links to large-scale circulation anomalies

摘要

We investigated short- and long-term changes in total and extreme summer precipitation and the characteristic patterns of atmospheric circulation and sea surface temperature (SST) anomalies related to wet summers over South Korea. Over the last century (1913-2012), the total and extreme summer precipitation showed a significant increase of 2.62 and 4.45 decade(-1), respectively. Because extreme summer precipitation increased more rapidly than total summer precipitation, the contribution of extreme precipitation to total precipitation increased significantly by 2.48 decade(-1). A two-peak rainy season was substantially intensified, with a slight shift and a large increase of precipitation during the monsoon break period, indicating a shortening of the monsoon break period. The 20-year return values of daily maximum precipitation increased at all stations except Mokpo, showing changes in the frequency of extreme events. During the last 40 years (1973-2012), the pattern of change in the precipitation indices was spatially heterogeneous, with a particularly significant increasing trend in extreme summer precipitation over the North-central portion of western South Korea. When compared with long-term trends over 1912-2012, recent short- term trends showed more rapid increases in all precipitation indices, with the exception of the number of consecutive dry days. In addition, the number of consecutive wet days (CWD) increased significantly during the last 40 years, whereas the long-term trend over the last century for CWD was not significant. These regional trends were confirmed by field significance at the 90 confidence level. From the composite analysis results, the positive anomalous North Pacific subtropical high, intensification of the upper-level westerly Jet over Korea and its vertical coupling with the anomalous strong low-level westerlies, and anomalous warm SST values in the western North Pacific region were linked to recent increases in extreme summer precipitation.