Evaluation of six indices for monitoring agricultural drought in the south-central United States

Drought indices are widely used for drought monitoring. This study evaluates the performance of six indices (Palmer's Drought Severity Index (PDSI), Palmer's Z-index, precipitation percent normal, precipitation percentiles, Standardized Precipitation Index (SPI), and the Standardized Precipitation Evapotranspiration Index (SPEI)) to determine which are most appropriate for monitoring agricultural drought in the south-central United States. Soil moisture and crop yield data for winter wheat, corn and cotton are used to assess the performance of drought indices. The results indicate that SPEI is the most representative of soil moisture conditions. The best drought index for crop yield varies depending on crop type and growth stage. Z-index and SPEI have relatively higher correlations with all the crop yields. However, when only considering years with weather and yield conditions that are substantially above or below normal, all of the drought indices are highly correlated with crop yield. Our results demonstrate that no single drought index can capture all aspects of agricultural drought in the south-central United States. Therefore, it is important to quantitatively evaluate multiple drought indices to determine which is most appropriate for the location and crop of interest.