Spatiotemporal evolution of temperature extremes onset times and their association with atmospheric circulations in the Poyang Lake basin, China.

The frequency and intensity variations of temperature extremes have received great attention in recent years. However, limited information is available on the variations in temperature extremes onset times. In this paper, we defined a set of evaluation indexes to quantify the onset times of temperature extremes. The spatiotemporal evolution of the onset times of temperature extremes in the Poyang Lake basin, China, was analyzed using daily temperature data from 87 meteorological stations in the area, covering the 1960-2022 period. The association between the onset times of temperature extremes and atmospheric circulations was further investigated in this study. We found that: (1) The onset times of all cold temperature events displayed a significant delaying trend (P < 0.01), while the onset times of all warm temperature events displayed a significant advancing trend (P < 0.05). (2) The variations in the onset times of temperature extremes were associated with atmospheric circulations. The Western Pacific Subtropical High-Intensity Index (WPSHI) and the Northern Hemisphere Subtropical High Area Index (NHSHAI) both correlated significantly negatively with the hot day onset date (SD30) (P < 0.01); the Arctic Oscillation (AO) showed significant positive and negative correlations with the frost onset date (SD0) (P < 0.05) and the warm season onset date (SD5) (P < 0.05), respectively. This study provides insights into the occurrence of extreme temperature events in the Poyang Lake basin, as well as useful references for implementing effective measures to reduce associated impacts.