Exploring the seasonal divergence among SPI, SPEI and SNEPI

The realistic assessment of drought is subjected to substantial uncertainty in the presence of a multitude of drought indicators owing to their mutually exclusive methodologies, variant data sources employed, and changing variable behavior. Though temperature-driven divergence analyses among drought indicators are not unknown, in this study the authors attempt to unravel the quantum of disagreements the newly developed Standardized Net Precipitation Distribution Index (SNEPI) possesses with its contemporary counterparts. The inherent aim of the authors is to highlight that (1) climate change impacts propagating to drought dynamics are not solely driven by increasing global temperatures, but also by changing precipitation characteristics, (2) identify regions where the operational use of SNEPI is maximum, and (3) identify various physical processes that govern the evolution of index divergences through an attribution analysis. We found a persistent negative disagreement or an enhanced occurrence of dry extremes in the annual divergence of SPEI with SPI and SNEPI, which questions the reliability on the traditional drought indices. However, the seasonal dispersion of this annual divergence revealed a strong spatiotemporal signal of monsoon droughts by SNEPI, which the traditional SPEI neglected. Further, the attribution analysis revealed that the radiative fluxes governed the evolution of SPEI-SPI divergence. Consequently, the divergence between SPEI and SNEPI is driven by the characteristics of wet spells, with the relationship strengthening in the monsoon season and tropical climate zones. The authors suggest an expansion in the operational value of SNEPI in the tropical regions where these discrepancies/disagreements are profound.