Spatiotemporal evolution patterns of compound drought-heat events in middle and upper reaches of Hanjiang River

Compound drought-heat events (CDHEs) are more disastrous than individual events.Therefore, monitoring their spatiotemporal evolution patterns is crucial for guiding disaster prevention and mitigation efforts.In this study, we employed the Standardized Compound Event Index (SCEI), Standardized Drought-Heat Index (SDHI), Blended Drought-Heat Index (BDHI), Standardized Precipitation Index (SPI), and Standardized Temperature Index (STI) to evaluate the spatiotemporal evolution characteristics of CDHEs, droughts, and heatwaves in the middle and upper reaches of the Hanjiang River during the summer season from 1961 to 2022.Furthermore, the monitoring capabilities of SCEI, SDHI, and BDHI in monitoring CDHEs were compared.The results indicated that: ① SPI, SCEI, SDHI, and BDHI displayed insignificant increasing trends (with Z-statistics of 1.08, 0.83, 0.46, and 0.46, respectively), whereas STI exhibited an insignificant decreasing trend (Z=-0.07).Accordingly, the trends in CDHEs, drought, and heatevents were not statistically significant.② The occurrence frequencies of CDHEs and drought events declines with increasing intensity, with the frequency of severe events ranging from 0 to 7.14%.③ The probabilities of occurrence for basin-wide drought events, heatwave events, and CDHEs were 8.1%, 16.1%, and 16.1%, respectively, all displaying insignificant decreasing trends.④ A comprehensive analysis revealed that BDHI outperformed SCEI and SDHI in monitoring CDHEs.These findings can provide references for basin water resources management and enhancing regional drought and disaster mitigation capabilities.