Assessment of drought in SPI series using continuous wavelet analysis for Gediz Basin, Turkey

Abstract

This study aims to estimate the short and long-term drought periodicities, and trend component using the continuous wavelet transforms. The applied approach introduces a new concept, the maxima line, which defines the most dominant component affecting the trend in Standardized Precipitation Index (SPI) time series. The analysis of the short and long-term drought cycles was performed with data from 15 stations located in Gediz Basin, at western part of Turkey, obtained during the recording period of 1960–2016. The change point in the SPI time series was determined graphically via the continuous wavelet power spectrum, and the obtained results were verified with Pettitt's test. The significant change points, in the northwest, east and southwest part of the basin, occurred by the beginning of 1980s, by the end of 1980s, and by the mid of 1990s, respectively. The most dominating periodicities affecting the trend were varying between 24 and 48 months for the short-term drought cycles, whereas they were varying between 96 and 162 months for the long-term drought cycles.