台灣百年來的乾旱分析研究 IV

Drought is one of important natural disasters in Taiwan. Numerous severe drought cases in the past few decades in Taiwan caused tremendous economic loss and great inconvenience in livelihood. After comparing with two other recent drought studies in Taiwan, a relatively reasonable definition, Taiwan Meteorological Drought index (TMD index), was established in this study. The results have been published in the article of “Construction of the Taiwan Meteorological Drought Index and the Analysis of Severe Drought Cases”. Through the TMD index, several historical severe drought cases in Taiwan were detected and characterized by significant seasonal variability in the annual cycle. During the dry period of Taiwan, changes of regional sea surface temperature (SST) and large-scale atmospheric circulations stabilize the atmosphere above Taiwan, which further triggers the state of extreme dryness on the island. The results have been published in “Atmosphere” as an article titled “Analysis of Severe Droughts in Taiwan and its Related Atmospheric and Oceanic Environments”. The precipitation from typhoons is one of the most indispensable water resources for Taiwan. The path of a typhoon not only affects the possibility of its invasion to Taiwan, but also plays a critical role of deciding whether the island will face a severe water shortage afterward. The work for this year analyzed the linkage between different locations of Pacific subtropical high and typhoon tracks, via categorizing several groups by the number of typhoon invasion day to Taiwan for each month in the typhoon season. After the analysis of composite, the result suggests that when the subtropical high retreats eastward, the accompanying steering flow guides typhoons to make an early recurvature toward Japan and South Korea. While the subtropical high further extends its property to the west covering Taiwan, the steering flow on the south transfers typhoons moving westward to the South China Sea. However, when the subtropical high lies in areas between the above two scenarios, the steering flow along the periphery of the subtropical high continuously sends typhoons toward Taiwan and the vicinity, which greatly increases the threat to the island. The results have been published in “Atmosphere” as an article titled “The climatological analysis of typhoon tracks, steering flow, and the Pacific subtropical high in the vicinity of Taiwan and the Western North Pacific”. The results of this study provide the possible linkage between droughts and typhoon variations.