Spatiotemporal evolution patterns of compound drought and heat events in the Upper and Middle of the Hanjiang River

The disaster effects resulting from the compound drought and heat events (CDHEs) are significantly stronger than those caused by single events. Therefore, monitoring their spatiotemporal evolution patterns is crucial for guiding disaster prevention and mitigation efforts. In this study, we evaluate spatiotemporal evolution characteristics of CDHEs、droughts and heatwave events during the summer season (1961-2022) in the Middle and Upper Hanjiang Basin (MUHJB) using the Standardized Compound Event Index (SCEI), the Standardized Drought-Heat Index (SDHI), and the Blended Drought-Heat Index (BDHI), along with the Standardized Precipitation Index (SPI) and the Standardized Temperature Index (STI). Furthermore, the monitoring capabilities of SCEI, SDHI, and BDHI for CDHEs are compared. The results indicate that SPI, SCEI, SDHI, and BDHI displayed non-significant increasing trends (Z_SCEI=0.83，Z_SDHI=0.46，Z_BDHI=0.46，Z_SPI=1.08). In contrast, STI exhibited a non-significant decreasing trend (Z_STI=-0.07). Accordingly, the trends in CDHEs, drought, and heat events were statistically insignificant. The occurrence frequency of CDHEs and drought events declines with increasing severity level, specifically, the frequency of severe events varied between 0 and 7.14%. The probabilities were 8.1% for region-wide drought events, 16.1% for region-wide heatwaves, and 16.1% for region-wide CDHEs. All these probabilities exhibited statistically insignificant decreasing trends. The integrated assessment indicates that BDHI provides superior performance compared to SCEI and SDHI for the monitoring of CDHEs. The research findings can offer valuable insights for guiding watershed water resources management and enhancing regional drought resilience and disaster mitigation capacity.