A comparative investigation on the applicability of the actual precipitation index (API) with the standardized precipitation index (SPI): the case study of Aras Basin, Turkey

This study aims to analyze drought using precipitation data from 6 meteorological stations located in the Aras Basin, one of Turkey’s 25 river basins. The precipitation data of the meteorological stations between 1969 and 2020 were used. Drought analysis were performed using the actual precipitation index (API), a new method, and the standardized precipitation index (SPI) based on the gamma distribution. The Kolmogorov–Smirnov test was used to determine the best distribution that fits the observed data. Three-, 6-, and 12-month periods are preferred. For Ardahan, Iğdır, and Kars stations, 3-, 6-, and 12-month API and SPI values are shown comparatively with graphics. Drought frequency values for all meteorological stations were obtained for 3-, 6-, and 12-month periods. Relative drought frequency values for both SPI and API are depicted in tables. According to the findings of this study, the driest station is Iğdır, while the wettest station is Ardahan. While extreme wet incidents are occasionally in the basin, extreme drought situations are observed. It has been determined that the climate of the basin is slightly arid.