The Influence of Decadal-scale Variations of East Asian Monsoon on Taiwan’s Extreme Dry Spells

Abstract:

The extreme dry spells in Taiwan show clear decadal-scale variations. The overall dry spell extremity became more sever after mid-1950s. The enhanced extremity showed clear seasonal dependence in different decades. In 1960s the enhanced extremity occurred during the earlier half of the summer months from May to July. During the decade from mid-1960s to mid-1970s the enhanced extremity occurred during the late summer and early autumn months from August to October, while it occurred in the mid-summer months of July and August during the 1980s. After 1990 the enhanced dry extremity was seen during the winter half year from October to March, the dry season in Taiwan. The enhanced dry extremity during the winter months increases the general concern that the dry season will become drier and the wet season will become wetter under the global warming trend, although the decadal-scale variations of the extremity during the wet season did not show concurrent relationship with the dry extremity. This paper shows that the summer dry spell extremes can be explained by more intense and westward extended western Pacific subtropical high (WPSH). The winter dry spell extremes can be explained by weaker East Asian winter monsoon. It is worth noting that the most recent and still going dry situation in Taiwan, which is the worst in 10 years, occurred concurrently with more westward extended WPSH during the 2014 summer and autumn and weaker than normal meridional mode of the East Asian winter monsoon during the 2014/15 winter. Understanding how extreme dry spells can be influenced by the East Asian monsoon variations is of critical importance to advance the climate change adaptation research in Taiwan.