An analysis of drought in the upper northern of Thailand using actual precipitation index

An analysis of droughts in upper northern Thailand using the standard precipitation index (SPI) and actual precipitation index (API) is the main focus of this paper. In this study, the summer rainfall data from 1991 to 2022 from three rain gauge stations, namely Nan, Phrae, and Phayao, are used to analyze drought. The gamma, lognormal, and Weibull distributions are applied to find the appropriate distribution for summer rainfall data. According to the results, the Weibull distribution could be the best fit for the summer rainfall data from Phrae and Phayao gauge stations, and the gamma distribution could be the best fit for the summer rainfall data from the Nan gauge station. The results of the comparison between API and SPI showed that both methods were able to detect the same extreme drought occurrences, with extreme droughts occurring at Nan station in 2013, Phrae station in 2010, and Phayao station in 1992. Consequently, from the results of this study, it can be concluded that the API provided a few different analyses than the SPI for drought assessment. Moreover, the API is for easy interpretation and application of the results to drought classification and monitoring. Therefore, the API can be beneficial for planning and solving the drought problem in Upper Northern Thailand.