Application of Transformation Techniques to Evaluate Drought
Abstract
The objective of this research was to compare data transformation methods, as well as to find the best data transformation technique for applying the standardized precipitation index to evaluate drought. Results of this study were as follows: part I was simulated data, Fourth-Root transformation was the best normal approximate transformation of gamma data. The Logarithm transformation was the best normal approximate transformation of lognormal data. The Haynes transformation was the best normal approximate transformation of Weibull data. Part II was real data, based on rain gauging stations of Ban Hong and Lee, Lamphun, Thailand to evaluate drought. Weibull distribution was found to be the most appropriate distribution to represent the Thai season rainfall amount in Ban Hong. Gamma distribution was found to be the most appropriate distribution to represent the Thai season rainfall amount in Lee. Ban Hong had extremely dry conditions in 2005 and 2014. Lee had extremely dry conditions in 1980, 2004, 2005 and 2014.
Keywords Transformation, Standardized Precipitation Index
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