Evaluating the performance of drought indices for assessing agricultural droughts in Argentina

This article presents an analysis of the response of the annual yield of rainfed maize crops in the Argentine Pampas Region to five drought indices (standardized precipitation index [SPI], standardized soil moisture index [SSMI], standardized evapotranspiration deficit index [SEDI], standardized precipitation-evapotranspiration index [SPEI], and standardized precipitation actual evapotranspiration index [SPET]) at different time scales (from 1 to 12 months). The idea of this work was to find the drought indices that best correspond to the interannual variability of maize yield and to use them in monitoring agricultural droughts. For this purpose, we correlated maize yields with different indices across all their time-scales. We selected the indices with the best overall response to yields and then performed a principal component analysis. The findings revealed that the SEDI and the SPEI displayed the highest correlations with maize yields, followed by SPI, while SPET exhibited the lowest correlations. Principal component analysis demonstrated a heightened predictive capacity of drought indices between February and March, particularly at 7–8-month scales, alongside the widely used 3-month temporal scale for monitoring agricultural droughts. The stronger correlations exhibited by SEDI and SPEI, which incorporate atmospheric evaporative demand into their calculations, suggest that water availability is not the sole meteorological factor influencing drought impacts. Atmospheric demand considers temperature and air humidity, factors that intensify plant stress conditions. These findings supported the importance of considering flexible drought indices adapted to different time-scales for accurate monitor of agricultural droughts, which can enhance planning and risk mitigation in crop production in the Pampas Region and beyond.