A 300-year Vietnam hydroclimate and ENSO variability record reconstructed from tree ring δ¹⁸O

A tree ring δ¹⁸O chronology is developed for the past 300years (1705-2004) using 6 cypress trees from northern Vietnam to reconstruct long-term hydroclimatic variations in the summer monsoon season. To the best of our knowledge, this is the first well-replicated tree ring δ¹⁸O chronology from Southeast Asia, as well as the longest yet produced. Response analyses reveal that tree ring δ¹⁸O is significantly correlated with temperature, precipitation, and the Palmer Drought Severity Index (PDSI) during the period May-October, with highest correlation to the PDSI. Our δ¹⁸O chronology accounts for 44% of the PDSI variance, and is in good agreement with a 52-year tree ring δ¹⁸O chronology from northern Laos (r=0.77), indicating that regional hydroclimatic signals are well recorded in the δ¹⁸O data. Spatial correlation analyses with global sea surface temperatures suggest that the tropical Pacific plays an important role in modulating hydroclimate over the study region. Further, the δ¹⁸O chronology correlates significantly with El Nio-Southern Oscillation (ENSO)-related indices, and is therefore used to reconstruct the annual Multivariate ENSO Index. Because previously published ENSO reconstructions are based mainly on proxy records originating from North America and/or the tropical Pacific, the future development of a tree ring δ¹⁸O network from mainland Southeast Asia could lead to an independent and more robust reconstruction of ENSO variability.