Defining Three Rainy Seasons and the Hydrological Summer Monsoon in Korea using Available Water Resources Index

Abstract

A new scheme that can define three rainy seasons, and the hydrological summer monsoon in Korea, has been proposed, examined, and verified to be effective. In the scheme, the Available Water Resources Index (AWRI) that is the accumulated precipitation value in which daily reduction of water, and the duration of accumulation are taken into account quantitatively.
With this scheme, the onset and ending dates of three rainy seasons are defined by such singularities as the smallest, the biggest, the minimum, and the maximum of the AWRI in a year. The intensities of these rainy seasons are defined by the value of the maximum AWRI, flood index, and drought index.
The first rainy season (Bom-Changma) starts in early April, when the minimum value of the AWRI in a year appears, and when the mean southerly wind at 925 hPa level become stronger then that at the 500 hPa level, and ends at May 15. The second rainy season (Changma) starts in late June and ends at 16-20 July. The third rainy season (Kaul-Changma) starts at mid August, and ends at 3-5 September that has the maximum value of the AWRI in a year, and that is the last date of mean southerly wind at the 925 hPa level.
Finally, the hydrological summer monsoon is proposed to be defined as the period of increasing water resources that is from the minimum to the maximum of the AWRI, from the onset of Bom-Changma till the end of Kaul-Changma. From a turning point of meridional wind system to the end of mean southerly wind in the low level atmosphere, and that is concurrent with the summer monsoon.