Performance of Multiple Drought Indices in Assessing Drought Impacts on Rice and Cassava Yields in Northeastern Thailand

ABSTRACT Agriculture in northeastern Thailand is highly vulnerable to drought, posing significant risks to crop production and rural livelihoods. Despite the economic importance of rice and cassava as staple and export crops, quantitative assessments of drought impacts on their yields remain limited. To enhance understanding of provincial scale drought impacts, the spatiotemporal relationships between drought conditions and crop yields were analysed. Spearman's rank correlation was used to evaluate the relationships between the standardised yield residual series (SYRS) and drought indices across various timescales, using the standardised precipitation index (SPI), the standardised precipitation evapotranspiration index (SPEI) and the standardised soil moisture index (SMI). The results revealed that yield losses are most sensitive to drought occurring during the period primarily corresponding to the vegetative phase (July to September) for major rice and the storage root bulking stage (September to February) for cassava, varying among provinces. Furthermore, the SPI and SPEI demonstrated stronger correlations with SYRS compared to SMI for both crops, highlighting their greater effectiveness in representing agricultural drought conditions. These findings underscore the necessity of province‐level drought adaptation planning that accounts for regional variations in crop sensitivity.