The weakening of autumn drought intensity in Korea after late 1990s

Abstract

Listen

Translate article

Using data of autumn (September–November) Palmer Drought Severity Index (PDSI) observed at 61 weather observation stations for 1974–2013 provided by Korea Meteorological Administration (KMA), the present study applies the statistical change-point analysis to the PDSI time-series in order to determine variability of autumn drought in Korea. The study result shows a trend that autumn drought in Korea has been weakened since 1998. This weakening trend is statistically significant at the 90% confidence level. Thus, a difference in autumn mean between 1998–2013 (PDSI: –1.6, which means ‘wetness’ condition) and 1974–1997 periods (PDSI: –0.6, which means ‘drought’ condition) is analyzed in order to determine the cause of the weakening of autumn drought in Korea in recent years. The analysis on 850 hPa stream flows shows that the Mascarene high (MH) is strengthened in the southeast sea of Madagascar and anomalous northeasterlies blown from this anomalous anticyclonic circulation are moved to the north along the eastern coast of Africa as the cross-equatorial flows and then move from India to the east towards the South China Sea (SCS) by the anomalous cyclone (Arabian low, AL) located in the south sea of the Arabian Peninsula. Then, the anomalous flows move to the north direction towards Korea and Japan by the anomalous anticyclone (western North Pacific subtropical high, WNPSH) located in the east of Japan and anomalous cyclone located in the East Asia continent thereby showing clear anomalous southerlies in those regions. The anomalous pressure system pattern of west low and east high type is a typical pressure system pattern revealed during summer in East Asia. That is, the anomalous southerlies played an important role in supplying warm and humid airs in the low latitude to mid-latitude regions in East Asia including Korea and Japan. In addition, the predictability for autumn drought in Korea is diagnosed using three anomalous pressure systems (MH, AL, WNPSH).