A comparison of the China-Z Index (CZI) and the Standardized Precipitation Index (SPI) for drought assessment in the Hirfanli Dam basin in central Turkey

In recent years, drought due to climate change cause significant negative effects on hydrological processes and water budget in many river basins around the world. Drought indices are used to determine the spatial and temporal characteristics of drought events. They are based on single or multiple variables and applied in different countries for the assessment of drought. Drought events occur frequently in Turkey, which has semi-arid climate characteristics. Drought is one of the most damaging natural disaster affecting many regions of Turkey. In this study, the capacity of the China-Z Index (CZI) and the Standardized Precipitation Index (SPI) were compared to identify drought periods at different time scales in the Hirfanli Dam basin in central Turkey. For this purpose, monthly precipitation data from 1960 to 2017 collected from six meteorological stations located within the basin were used. The SPI and CZI values were calculated at 1-, 3-, 6-, 9- and 12-month time scales, and the results were compared. The relationships between the outputs of the drought indices were statistically examined. The results indicated that the SPI and CZI values have high correlation coefficients at long time scales (9 and 12 months). It was observed that as the time scale decreased, the correlation between the two drought indices gradually weakened. It was determined that both indices can be utilizied for drought forecasting studies at relatively longer time scales in the study area. It is thought that the results of the study will contribute to the regulation of the management and planning of water resources in river basins in accordance with climatic changes that has become more important in recent years.