A sudden change in summer rainfall characteristics in Korea during the late 1970s

We have examined long‐term climate change in Korea by studying daily rainfall data over a period of 48 years (1954–2001). The results show that there is a more frequent heavy rainfall anomaly larger than 100 mm per 3 months in recent years. For further investigation, we divide the whole period into two 24 year intervals, 1954–77 and 1978–2001. Two well‐defined rainfall peaks occur during summertime in both intervals. During the earlier interval, primary and secondary rainfall peaks are found in early July and early September, respectively. In the later interval, on the other hand, the secondary peak is found in mid–late August, mainly attributed to enhanced heavy rainfall (≥30 mm day −1 ) events. Although a similar shift occurs in the primary peak, it is much smaller. Thus, the relatively dry spell between the two peaks becomes shorter in the later interval compared with the earlier one. The domain‐mean geopotential height at 700 hPa (Φ 700 ) over mid‐latitude Asia (30–50° N, 60–120° E) for the summer also experienced a sudden increase in the mid 1970s. A comparison of the spatial distribution of Φ 700 between the two intervals shows large positive differences over the central‐eastern Asian continent in the later interval. In contrast to the positive anomaly of Φ 700 in the later interval, there is a decreasing trend in surface temperature. The increased Φ 700 introduces a stronger northerly wind over East Asia and possibly produces a moisture convergence, enhanced convective activity, and heavy rainfall over the region, in particular over Korea and central China. Copyright © 2003 Royal Meteorological Society.