Effects of the Pacific Decadal Oscillation on Thailand monsoon rainfall derived from a 194-year tree ring width chronology of teak trees from northwestern Thailand.

Abstract

Thailand is a predominantly agricultural country. An understanding of the dominant driver of decadal-scale changes in Thailand monsoon (TM) rainfall trends is particularly important in terms of agro-meteorological information and monsoon predictions. In this study, a 194-year tree ring chronology of teak trees in northwestern Thailand was developed. Correlations between the tree ring width index (i.e., the Susa index) and climate variables confirmed that this index can be used as a proxy for rainfall in the early monsoon season from May to July. Similar variations with other regional tree ring chronologies confirmed the reliability of the climate signals embedded in the tree ring widths. The possible relationship between the Susa index-based TM rainfall and the Pacific Decadal Oscillation (PDO) was examined. Spectral analysis showed statistically significant PDO periodicities of between 22 and 24years. The spatial correlations detected across the key regions of the PDO revealed associations with the north Pacific sea surface temperature during recent decades. The long-term relationships between the Susa index and the PDO were nonstationary at the decadal timescale. Positive correlations were found for AD 1824-1875 and AD 1900-1955, whereas negative relationships prevailed for AD 1876-1899 and 1956-2017. The El Niño Southern Oscillation-related anomalous TM was indeed stronger during both the warm and cold phases of the PDO. The PDO is therefore identified as a driving factor of decadal climate variability. This study leads the way to understanding the changes in the TM-PDO relationship over time and demonstrates the utility of teak tree ring width as a potential proxy for PDO teleconnection.