SDI for regional drought characteristics of the Northern Taiwan

The impact of global climate change in recent years has led to changes in rainfall patterns, resulting in uneven rainfall distribution and the birth of polarized rainfalls. Taiwan is a region located in a subtropical climate zone and one that is characterized bydistinct wet and dry seasons; such a characteristic has created a comparatively more severe polarized rainfall situation in which streamflow is drastically influenced by amount of rainfall. This has created considerable differences in streamflow between wet and dry seasons and instances of hydrological droughts are prevalent. Therefore, to effectively manage the increasingly scarce water resources, streamflow characteristics during dry seasons must be explored and assessed. In this study, streamflow characteristics of the Northern region of Taiwan were analyzed using the streamflow drought index (SDI) and the Markov chains, in which results showed that 2002 marked the turning point from which the severity of droughts increased in both the Lanyang River and Yilan River basins; in 2002, the severity of wet condition in the Lanyang River basin increased, whereas the severity of droughts in the Yilan River basin increased. When investigating droughts, the 3-month (Nov. to Jan.) and 6-month (Nov. to Apr.) analysis results may be used to show the drought characteristics. A drought probability analysis made using the Markov chains indicated that the probability of dry and wet conditions in the Lanyang River basin are all higher than that of the Yilan River basin. In particular, during dry seasons (from Nov. to Apr.), the likelihood of the Lanyang River basin to experience severe droughts is 20.6%, whereas that of the Yilan River basin is 3.4%. This study also found that the short-term probability, severity, and frequency of dry and wet conditions may be analyzed using the Markov chains, and that the said results can be used to predict the severity and probability of long-term dry and wet conditions.