Polarizing rain types linked to June drought in the Korean peninsula over last 20 years

Abstract

We observe a notable decreasing trend of June rainfall over the Korean peninsula in recent 20 years. This drought condition is found to be linked to the polarizing trend of rainfall intensity; more non‐rain and drizzle‐like rain, less moderate‐intensity rain, and more heavy rain events. Overall, the June drought over the Korean peninsula is found to be associated with less occurring moderate‐intensity rain. This feature is interpreted as that the dominant warm‐type heavy rain systems with a medium storm height tends to be less frequent while cold‐type heavy rains characterized by taller storm become more frequent during last 20 years. The northwestward expansion of the North Pacific high in June appears to weaken the continuous moisture supply to the Korean peninsula, which is a main element of forming the warm‐type heavy rain there.

Possible Mechanisms of Long-Term Trend of June Rainfall over the Korean Peninsula

“…3b). These two trends are similar to changes in the May-June rainfall noted in Yim et al (2014) for the period of 1979-2010, and also consistent with Song and Sohn (2019) results for recent 20 years (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017) showing the decreased June rainfall over the Korean peninsula.…”

“…However, focusing on more recent trend analysis after 1998, it had been reported to accelerate to −70.55 mm decade −1 . This study using ASOS 56 stations (excluding four island stations) also exhibits similar results with Song and Sohn (2019), except for statistics ( Fig. 1).…”

“…Since precipitation over the Korean peninsula has a large interannual variability, the rainfall trend often depends on the analysis period under consideration. Song and Sohn (2019) found that the June rainfall from ASOS 60 stations in South Korea exhibits a gradual decrease of −27.72 mm decade −1 since 1978. However, focusing on more recent trend analysis after 1998, it had been reported to accelerate to −70.55 mm decade −1 .…”

“…Most of the previous studies (e.g., Kwon et al 2007;Ding et al 2008Ding et al , 2009Han et al 2015;Ueda et al 2015;Xu et al 2015;Zhang and Zhou 2015;Piao et al 2017;Zhang et al 2019) focused on changes in rainfall and associated largescale circulation during the summer months of June-August (or September). However, as discussed in Song and Sohn (2019), the decreasing trend of rainfall around the Korean peninsula was evidently found only in June during the summer months, suggesting the EASM circulation in June may have changed differently from the whole summer. The recent June droughts over Korea and related large-scale circulation changes have not been fully understood yet.…”

“…In association with Changma, the June rainfall over the Korean peninsula has exhibited a notable decreasing trend during recent four decades (Song and Sohn 2019). It was noted that the northwestward propagation of the WNPSH and southwesterly water vapor flux over the Korean peninsula were much weakened during the recent 20 years, but the mechanism to explain why the WNPSH has been changed was not provided.…”