Optimal Probability Distribution and Applicable Minimum Time-Scale for Daily Standardized Precipitation Index Time Series in South Korea

The Standardized Precipitation Index (SPI) is a standardized measure of the variability precipitation and widely used for drought assessment around world. In general, probability distribution to calculate SPI in many studies Gamma. addition, monthly time-scale applied assess based on atmospheric moisture supply over medium-to-long term. However, distributions other than Gamma are various regions, need daily emerging as concerns about fresh increase. There two main innovations our work. first that we investigate optimal SPIs rather SPIs, second address issue determining minimum can be when applying time-scale. this study, minimum-applicable calculating using time series observed 42 years at 56 sites South Korea. Six candidate (Gumbel, Gamma, GEV, Log-logistic, Log-normal, Weibull) ten time-scales (5 day, 10 15 21 30 60 90 180 270 365 day) were SPI. A chi-square test AIC appropriate each time-scale, normality derived from compared. Weibull was suitable short days or less, while GEV longer more. overall, found best distribution. While there some regional variations, could per season follows: spring summer, fall, winter. It shown depends how zero values included moving cumulative-precipitation series, it have less 2.5%. Finally, applicability investigated.