Recent Changes in Temperature Extremes During Cold Season Over Northern Vietnam and Teleconnections With ENSO , IOD , NAO and AO

This study analyses the spatial trends of 10 temperature extreme indices and their relationships with the El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) across northern Vietnam during the cold season (November to March) from 1981 to 2021. Statistically significant strong warming trends are detected across the region, consistent with findings from previous studies in Southeast Asia. The frequency of warm days/nights (TX90p/TN90p) increases significantly by 1%–2.5% per decade, while cold days/nights (TX10p/TN10p) decrease by 1%–3% per decade, though with weaker significance. Both the warmest and coldest day/night temperatures exhibit significant warming, with a more pronounced increase in the former. This study also found that among four prominent natural modes of climate variability, ENSO and the IOD play a dominant role in regulating temperature extremes over northern Vietnam during the cold season from 1981 to 2021. ENSO exhibits an asymmetric influence, with more frequent and intense warm extremes, and less intense, spatially limited cool extremes. Correlation analysis indicates that ENSO and the IOD act as independent drivers of climate variability in the region. In contrast, the correlations with the NAO and AO are weak, negative and not statistically significant.