NOAA/WDS Paleoclimatology - Central Vietnam 660 Year SPEI Index Reconstruction

We present the first crossdated tree ring record from central Vietnam, derived from the growth rings of the rare cypress Fokienia hodginsii from the mountains of Quang Nam Province near the Laos border. The Quang Nam Fokienia hodginsii time series (QNFH), based on the crossdated sequences of 71 increment core samples from 37 mature trees, is the third published dendrochronological record from this species. The record extends 667 years from AD 1347 to 2013 and exhibits a mean series intercorrelation of 0.526, similarly significant with the first two published Fokienia hodginsii records: 0.474 for Mu Cang Chai (MCFH) and 0.578 for Bidoup-Nui Ba National Park (BDFH) in the north and south of Vietnam, respectively. The Expressed Population Signal (EPS) for the QNFH record exceeds the generally accepted threshold of 0.85 back to AD 1567, but remains above 0.8 back to 1550. Similar to the MCFH and BDFH records, QNFH expresses statistically significant linkages to regional hydroclimate metrics and the El Niño-Southern Oscillation. Here we present a reconstruction of the Standardized Precipitation Evapotranspiration Index for the month of April, averaged over a large region of Southeast Asia. As with prior studies we demonstrate that cool phase (La Niña) and warm phase (El Niño) events are linked to regional wet and dry conditions, respectively, with linkages to modulation of the surface water temperature over the adjacent sea to the east of Vietnam as well as the Indian Ocean. A late eighteenth century megadrought that is expressed widely across South and Southeast Asia, and notably from the MCFH and BDFH records described above, is not as pronounced in Central Vietnam and we explore the reasons why.