Abstract: Yilong Lake, one of the nine plateau lakes in Yunnan, is a typical shallow plateau lake with high sensitivity to climate change. Understanding how extreme climate variability affects the basin is therefore critical for regional ecological security and socio-economic development. Based on daily meteorological data from 1979 to 2023 in the Yilong Lake Basin, we analyzed the trends of extreme climate changes and their relationships with atmospheric circulation modes using linear regression, Mann-Kendall test, wavelet transform coherence (WTC) analysis, and multiple wavelet coherence (MWC) analysis. The results showed that rainfall intensity and air temperature increased significantly from 1979 to 2023, indicating a pronounced warming-wetting trend. Stronger Pacific Decadal Oscillation (PDO) and North Atlantic Oscillation (NAO) phases were associated with higher frequencies of heavy precipitation events. Enhanced East Atlantic/West Russia (EA/WR) patterns corresponded to wetter and cooler conditions, and stronger El Niño-Southern Oscillation (ENSO) phases corresponded to hotter and drier conditions. Changes in individual extreme climate indices were synergistically influenced by the combinations of atmospheric circulation modes. Based on the percent area of significant coherence (PASC) of multiple wavelet, the three-mode combination PDO-NAO-EA/WR dominated the variability of consecutive dry days (PASC=26.1%), consecutive wet days (22.5%), cold day index (20.5%), summer days (18.7%), warm night index (13.5%), and the warm day index (10.6%). The four-mode combination PDO-NAO-EA/WR-ENSO dominated the variability of the cold night index (11.0%). PASC differences among multi-mode combinations were not significant for indices such as max 1-day precipitation amount, heavy precipitation days, very wet days, and simple daily intensity index.

Key words: extreme climate index, atmospheric circulation mode, wavelet transform coherence, multiple wavelet coherence, Yilong Lake Basin