Drought propagation, the process by which meteorological drought evolves into hydrological drought, significantly affects water resource dynamics within watersheds. A thorough understanding of its mechanisms and patterns is crucial for improving drought monitoring and management strategies. This study assessed the spatiotemporal patterns of drought propagation in the Karun 3 watershed from 1984 to 2023. For this purpose, monthly precipitation data from 27 stations (20 rain-gauge and 7 synoptic) and discharge data from 3 hydrometric stations located at the outlets of the Upper, Middle, and Lower Karun sub-basins. Meteorological and hydrological droughts were identified using the Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI), respectively. We then extracted five key drought characteristics: drought frequency, degree, maximum duration, total duration, and spatial coverage. Finally, these characteristics were integrated to calculate the Comprehensive Drought Intensity Index (DCI) and the Comprehensive Drought Propagation Intensity Index (DCPI), providing an integrated assessment of the drought propagation process.
The results showed that the change tendency rate of SRI12 (−0.0604) was approximately twice that of SPI12 (−0.0311). Hydrological drought frequency increased from zero events between 1984 and 1993 to eight events between 2014 and 2023, while the mean drought degree rose from 0.855 to 1.199. The total duration of drought events reached four months in the final decade, with over 66% of the watershed area affected by hydrological drought in approximately 70% of the years during this period. Statistical analysis confirmed a significant positive correlation between meteorological and hydrological droughts across the entire watershed and all sub-basins (P < 0.01). The DCPI increased from 0.0143 very weak in 1984–1993 to 1.057 strong in 2014–2023. At the sub-basin level, the Lower Karun recorded the highest DCPI value (1.50), while the Middle Karun observed the lowest (1.09), indicating substantial spatial heterogeneity in drought propagation across the watershed.