Appraisal of seasonal drought characteristics in Turkey during 1925–2016 with the standardized precipitation index and copula approach

Drought is caused by the imbalances in the factors that make up the hydrological cycle, especially the rainfall. Droughts triggered by climate change can occur anywhere in the world. This study aims to conduct a detailed seasonal drought analysis through the monthly precipitation statistics of 126 observational points in Turkey during 1925–2016. The drought analysis was performed for four different periods: 1925–1949, 1950–1974, 1975–1999, and 2000–2016. First, the standardized precipitation index values were calculated with the Pearson Type III distribution. The 3-month period, used in seasonal drought analysis, was preferred. Information about the course of drought was obtained with the Mann–Kendall trend analysis. The severity, duration, and frequency of drought were found with the Theory of Runs model. The joint return period of drought severity and drought duration were obtained with the copula approach. The mapping was done with the inverse distance weighted method. The findings indicate that the lowest SPI value (− 2.12) was observed in spring 1972 and the highest SPI value (2.14) was observed in winter 1941. Very dry conditions were recorded with a frequency of 16% in the spring season of the 1925–1949 period; the most normal arid conditions were documented in the autumn season of 1950–1974 with a frequency of 52%. Extreme drought conditions were reported in the spring season in 1992. While there was an insignificant increase in drought in spring, summer, and winter, a significant increase was observed in autumn especially interior parts of Turkey. Theory of Runs results indicate that the highest intensity, with a value over 2, was observed in the southeast of Turkey during the winter and spring seasons during the 1925–2016 period. The Frank copula function was found to be the most suitable function in calculations of the drought severity and duration calculation for Turkey. The return periods of weak, moderate, and severe droughts were between 127.53 and 78.96, 68.85 and 59.60, 60.28 and 57.65 months, respectively. It was determined that the drought severity increased in the inner regions during the 20- and 100-year drought return periods with the values varying between 5 and 16, 7, and 32, respectively.