Evaluation of the Usability of the Rainfall Anomaly Index (RAI) Instead of the Standard Precipitation Index (SPI)

In this study, it is aimed to examine the usability of the Rainfall Anomaly Index (RAI) method instead of the Standard Precipitation Index (SPI) method. In order to make the RAI method usable instead of the SPI method, a modification technique different from the literature in the study. The results obtained with the RAI method (mRAI) modified by the proposed method were compared with the results obtained with the SPI method and other studies in literature. Pearson Correlation Coefficient (PCC), Cohen’s Kappa Statistic and Bland and Altman Plot methods were used to evaluate the agreement of the results. According to the Kappa Statistic and Bland and Altman Plot methods, it was determined that the results obtained with the mRAI method gave the best results in all time periods. For long-term drought values (12, 24 and 48 months), mRAI results and SPI results were found to be in good agreement and regional coefficients that can be used in the calculation of long-term drought values with the mRAI method were proposed for the selected region. As a result, it was evaluated that the mRAI method can be used instead of the SPI method in the calculation of long-term drought values. © The Author(s), under exclusive licence to Shiraz University 2024.