Comparative Analysis of Drought Indices for Different Climatic Zones in Benin

Abstract The Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) are essential indices for assessing drought characteristics. This study evaluates the performance of SPI and SPEI across three climatic zones in Benin: zone 1 (northern region), zone 2 (central region), and zone 3 (southern region). The evaluation is conducted through analyses of temporal variations, the Mann-Kendall trend test, Pearson correlation, and cross wavelet transformations. Additionally, the relationship between Standardized Relative Humidity Index (SRHI) and both SPI and SPEI were analyzed to identify the most effective index for drought monitoring in Benin. Results revealed increasing consistency in the temporal variations of the SPI and SPEI as the time scales extended across all areas, but significant differences existed in the drought trends identified by the two indices in some areas. Overall, a strong correlation was observed between the two indices. The comparison with the SRHI reveals that both the SPI and the SPEI exhibit a weak positive correlation across all time scales, with the exception of the SRHI–3 and SPEI–3. This exception indicates that at the three-month timescale, SPEI can effectively substitute for SRHI in monitoring drought. Consequently, SPEI demonstrates greater utility than SPI in this context however, the adaptability of the SPI and SPEI may vary depending on the periods and the natural characteristics of the regions.