Spatio-Temporal Agreement Between Standardized Precipitation Index (SPI) and Rainfall Anomaly Index (RAI) for Drought Monitoring: A Case Study of Vadodara District, Gujarat

Drought is among the most ruinous natural disasters, and its frequency and severity are likely to rise because of climate change, especially in susceptible areas such as Gujarat, India. A precise assessment of drought is critical for early warning, mitigation planning, and sustainable water resource management. This study evaluated annual meteorological drought in the Vadodara district over 30 years (1991–2021) using daily rainfall data obtained from the State Data Water Center (SDWC), Gandhinagar, and Anand Agricultural University. The assessment employs two widely recognized indices: the Standardized Precipitation Index (SPI) and the Rainfall Anomaly Index (RAI). Eleven meteorological stations at the district level were used to classify drought, wet, and normal years based on these indices. A spatiotemporal concordance analysis was performed to analyze the congruence of the SPI and RAI in describing drought occurrence. The results indicated moderate agreement among the indices, with a consistency of 30% at Kawat and 50% at Pilol and Rampura. These differences mirror the effects of localized climatic and topographic factors, along with methodological differences between the RAI and SPI. Although both are useful for detecting droughts, their partial agreement highlights the significance of a multi-index approach for increasing the reliability of drought monitoring. The results help improve the knowledge of index performance and inform the construction of more reliable regional drought early warning systems and water resource management.