As shown in Table 4, the correlation results determined by the coefficient of determination (R2) among SPI, RDI, and SPEI for all sites in the spring (February–May), summer (June–September), and six-month (March–August) time scales range from 0.772 to 0.995. The correlation value for the Ziway station is relatively low. The majority of stations exhibit a substantial correlation between the three indices and were consistent throughout the research area.

Table 4

The correlation results based on the coefficient of determination (R2) for the three drought indices (SPI, SPEI, and RDI) for six meteorological stations

Time periodDrought indicesButajiraZiwayKulumsaSagureWulbaregHawassa
Spring (February–May) SPI and RDI 0.993 0.982 0.995 0.981 0.978 0.970 
SPI and SPEI 0.952 0.851 0.942 0.928 0.970 0.923 
RDI and SPEI 0.971 0.926 0.951 0.974 0.991 0.962 
Summer (June–September) SPI and RDI 0.969 0.889 0.971 0.946 0.942 0.976 
SPI and SPEI 0.940 0.820 0.881 0.903 0.964 0.956 
RDI and SPEI 0.958 0.953 0.910 0.942 0.988 0.986 
Six months (March–August) SPI and RDI 0.989 0.881 0.978 0.960 0.949 0.954 
SPI and SPEI 0.901 0.772 0.903 0.916 0.962 0.933 
RDI and SPEI 0.926 0.968 0.916 0.975 0.983 0.989 
Time periodDrought indicesButajiraZiwayKulumsaSagureWulbaregHawassa
Spring (February–May) SPI and RDI 0.993 0.982 0.995 0.981 0.978 0.970 
SPI and SPEI 0.952 0.851 0.942 0.928 0.970 0.923 
RDI and SPEI 0.971 0.926 0.951 0.974 0.991 0.962 
Summer (June–September) SPI and RDI 0.969 0.889 0.971 0.946 0.942 0.976 
SPI and SPEI 0.940 0.820 0.881 0.903 0.964 0.956 
RDI and SPEI 0.958 0.953 0.910 0.942 0.988 0.986 
Six months (March–August) SPI and RDI 0.989 0.881 0.978 0.960 0.949 0.954 
SPI and SPEI 0.901 0.772 0.903 0.916 0.962 0.933 
RDI and SPEI 0.926 0.968 0.916 0.975 0.983 0.989 
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