ANALYSIS OF INCONSISTENCIES AMONG DROUGHT INDICES USING THE INNOVATIVE DROUGHT CLASSIFICATION MATRIX (IDCM)

7 th INTERNATIONAL ISTANBUL CURRENT SCIENTIFIC RESEARCH CONGRESS, İstanbul, Türkiye, 21 - 22 Ağustos 2025, cilt.1, ss.433, (Özet Bildiri)

Numerous drought indices (e.g., SPI, SPEI, SSI) are extensively employed in the literature to

monitor and characterize drought events. Each index may yield different results over a given

period, depending on underlying physical processes, a frequently observed and expected

phenomenon. However, discrepancies among these indices pose a significant challenge for

drought assessments. Since these inconsistencies are difficult to validate and resolve in

practice, they are often overlooked in research. The sensitivity of indices to different

meteorological and hydrological processes, specific parameters, and temporal scales naturally

affects the analysis outcomes. Among commonly applied drought metrics, the Standardized

Precipitation Index (SPI) reflects primarily meteorological conditions as it only considers

precipitation data, and thus does not directly provide a hydrological assessment based on its

results. In contrast, the Standardized Precipitation Evapotranspiration Index (SPEI), which

integrates precipitation with evapotranspiration, generally produces more negative index

values during rising temperatures. The Standardized Streamflow Index (SSI), more responsive

to streamflow data, is considered a more reliable indicator for evaluating hydrological drought

events. This study aims to investigate inconsistencies among drought indices. For this

purpose, data from adjacent meteorological and streamflow gauging stations within the Konya

Closed Basin were used to compare SPI, SPEI, and SSI results at a one-month time scale

through the Innovative Drought Classification Matrix (IDCM). The findings reveal that index

outcomes diverge as a function of physical processes. The IDCM methodology quantitatively

demonstrated the degree of agreement among indices and highlighted that low correlations

may lead to misleading interpretations, particularly in short-term assessments. In conclusion,

this comparative analysis over a representative sub-region of the Konya Closed Basin

emphasizes addressing index inconsistencies. It highlights the need for robust,

multidimensional assessment tools for more reliable drought monitoring and decision-making.