Comparison of Two Threshold Based Methods for Identifying Regional High Temperature Events in Yangtze River Basin

Under the background of global warming, the frequent occurrence of extreme high-temperature events has intensified the contradiction between water supply and demand in river basins. To objectively reveal the spatiotemporal distribution characteristics and evolution trends of high-temperature events in the Yangtze River Basin, this study used daily maximum temperature data from 735 national meteorological stations in the basin from 1961 to 2022. Regional high-temperature events during the warm season in the Upper (UPYR) and Middle-Lower (MLYR) reaches were identified using both absolute and relative threshold methods. A comparative analysis of the applicability and sensitivity of the two methods was conducted from multiple dimensions, including frequency, spatiotemporal distribution, and comprehensive intensity. The main conclusions are: ①There were 299 and 383 high-temperature events in UPYR and MLYR detected by the absolute threshold method, while 423 and 410 events were identified by the relative threshold method. The relative threshold method exhibits higher sensitivity to high-temperature events in UPYR. ②Absolute threshold-based events concentrate in midsummer (July–August), whereas relative threshold-based events are more evenly distributed across May–September. The absolute threshold demonstrates stronger responsiveness to extreme high-temperature periods. ③ The duration of events identified by the absolute threshold ranges from 7.1 to 8.7 days, compared to an average of 5.4 days for relative threshold events, indicating greater stability in capturing prolonged heat processes via the absolute threshold. ④ Both methods show over 60% consistency in identifying typical high-temperature years and reveal a significant upward trend in frequency and intensity of high-temperature events over the past six decades, with extremeness becoming notably more pronounced since the 21st century. Nevertheless, the relative threshold is more sensitive to climate change responses, while the absolute threshold better characterizes high-intensity extreme heat events. The findings provide a scientific basis for advancing research and formulating mitigation strategies pertaining to extreme high-temperature events in the basin.