A tree-ring cellulose δ¹⁸O-based July-October precipitation reconstruction since AD 1828, northwest Thailand

A tree-ring δ¹⁸O chronology for the period 1828-2000 was developed from four Pinus merkusii trees, to find a reliable proxy for reconstructing precipitation in northwest Thailand. Inter-tree δ¹⁸O correlations were high during the entire period (r=0.57-0.79). The tree-ring δ¹⁸O chronology shows significant negative correlations with regional July-October precipitation during the period 1901-2000 (r=-0.62) and with July-October river flow (r=-0.54), and is in good agreement with a shorter tree-ring δ¹⁸O chronology from living Pinus kesiya in northwest Thailand. The spatial correlation analysis between tree-ring δ¹⁸O and regional July-October precipitation also support that the tree-ring δ¹⁸O of P. merkusii is a promising proxy to reconstruct precipitation in northwest Thailand. The tree-ring δ¹⁸O-based July-October reconstruction, which accounts for 37.6% of the precipitation variance, shows a close relationship with El Niño-Southern Oscillation (ENSO) during the period 1871-2000, with the exception of during the past two decades; the exception may be related to the southeastward shift of the descending limb of Walker circulation and increased frequency of central Pacific ENSO.