Investigation of the effects of potential evapotranspiration method on meteorological drought trend: Eastern Black Sea Basin example

Drought has been one of the most interesting issues in recent years. Drought is a very complex disaster because it has many unknowns and uncertainties, such as not having a specific limit, the slow rate of occurrence, and the inability to determine the extent of damage that will occur if it occurs. Drought analysis studies are carried out using historical data to evaluate this complex drought and determine measures. In this study, the meteorological drought in the Eastern Black Sea Basin, located in the north-east of our country, was analyzed with the Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) methods with the help of meteorological parameters measured between 1965-2019. In order to evaluate the drought in the region, index values were calculated at 3, 6 and 12 month time scales. Hargreaves and Thornthwaite method was used to calculate the potential evapotranspiration (PET) value required to calculate the index value in the RDI method. The correlation of RDI_H and RDI_T index values, calculated through PET values obtained using two different PET calculation methods, with SPI values was evaluated. In addition, the trends of the index values obtained as a result of each drought method were obtained by the Mann-Kendall and Sperman Rho methods. In addition, the magnitude of the change in index values was determined by the Sen's slope method. Although the average precipitation value of the study region is greater than the average precipitation value of Turkey, the percentage of drought occurrence in many stations was greater than 50% in some time periods. The correlation coefficient between SPI and RDI_H indices was more significant than the value between SPI and RDI_T methods across the entire study region at 3, 6 and 12 time scales. It has been determined that the correlation between SPI and RDI_T indices is relatively low at stations in regions with high altitudes, especially in winter.