Comparative Assessment of Standard Precipitation Index and Standard Precipitation Evapotranspiration Index as Drought Evaluation Tools in Coastal Winneba-Ghana

In coastal Winneba-Ghana, drought occurrence negatively affects the ecosystems and agriculture and threatens food security and socio-economic livelihoods. Nevertheless, there exist dearth of information on a detailed statistical evaluation of drought indices over this area. This study made a comparative assessment of Standard Precipitation Index (SPI) and Standard Precipitation Evapotranspiration Index (SPEI) over coastal-Winneba. A daily temperature and rainfall data from 1980-2019 acquired from the Ghana Meteorological Agency was used to perform SPI and SPEI. Pearson correlation coefficient and cross-correlation, and Bland and Altman plot were used to test for the strength and direction and the degree of agreement, respectively between SPI and SPEI. Results showed a strong and positive association between SPI and SPEI (0.90, 0.91, 0.84, and 0.93) at 1-, 3-, 6-, and 12-month timescales, respectively. Results again, showed a good degree of agreement between SPI and SPEI (-0.06138, -0.00736, -0.05211, and -0.01810) at 1-, 3-, 6-, and 12-month timescales, respectively. Results further, showed that while both SPI and SPEI correlated strongly with each other, SPEI performed better in the detection of severe and extreme droughts at all timescales than SPI. Additionally, results showed that in the absence of temperature data to perform SPEI, the SPI can be used since the study found an acceptable degree of agreement scores between SPI and SPEI at all timescales in the study area. The study, therefore, recommends the utilization of numerous drought indices in drought performance assessment at a particular region or locality to arrive at a strong decision.