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The long-term effects of climate change and climate extremes have been associated with changes in tree growth and forest productivity worldwide, and dendrochronological analyses are important tools that can be used to investigate the influence of climatic forces on tree growth at a particular site. In this study, a 180-year tree ring width chronology (spanning from 1843 to 2022) of living pine trees (Pinus latteri) in Tak province, northwestern Thailand, was developed. The analysis of the climate–tree growth relationship indicated the influences of the annual total rainfall (r = 0.60, p < 0.001) and annual averaged relative humidity (r = 0.47, p < 0.001) on tree growth in this area. Anomalously high (for example, in 1853, 1984, 2011, and 2018) and low growths (for example, in 1954, 1983, 1992, and 1996) were found. Growth anomalies in the Thai pine in this study were related to changes in abnormal and extreme rainfall (r = 0.94, p < 0.001) and the El Niño Southern Oscillation (ENSO). Our results confirm that rainfall and relative humidity are the main climatic factors regulating the radial growth of Thai pine. This finding could be an important contribution to further research on the effects of climate change and extreme weather events on the vulnerability of tropical and subtropical trees in this region. [ABSTRACT FROM AUTHOR]

We present a new teak (Tectona grandis L.f.) tree-ring stable oxygen isotope (δ18OTR) chronology from Mae Tuen (MT) site, Tak province, northwestern Thailand at inter-annual (167-year, A.D.1850–2016) and intra-annual (A.D.2006–2016) timescales. The inter-annual δ18OTR chronology showed a significant negative correlation (r = −0.678, p < 0.01) with the May–October amount of regional rainfall obtained from CRU TS4.03. We established a linear regression model that explained 46.0% of the actual rainfall variance and reconstructed monsoon season rainfall back to A.D.1850. The seasonal variations in moisture conditions were reflected in inter-annual δ18OTR variability. The rainfall amount and δ18O in precipitation (δ18Op) mainly controlled intra-annual variations in teak δ18OTR. These results show that the variation in Thai teak δ18OTR is dominated by rainfall, highlighting the strength of δ18OTR as a monsoon rainfall proxy. [ABSTRACT FROM AUTHOR]

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 24 years. 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. [ABSTRACT FROM AUTHOR]

Thailand monsoon is located in the transition zone between the Indian and western North Pacific monsoons. Assuredly, proxy climate data from this area could improve our understanding of the nature of Asian monsoon. Tree rings and stalagmites from this area are two potential materials for high-resolution paleoclimate reconstructions. However, a comprehensive understanding of these multiproxy records is still a challenge. In this study, a 76-year tree ring cellulose oxygen isotope value (δ18O) of a teak tree from northwestern Thailand was developed to test its climatic significance and potential for multiproxy climate reconstruction. The results indicate that the interannual variability of cellulose δ18O can be interpreted as a proxy of rainfall in the early monsoon season (May to July rainfall) as well as a proxy of relative humidity. Comparisons with speleothem proxies from the same locality and tree ring records from wider geographical areas provide a basis for developing a multiproxy approach. The results from a teleconnection analysis reveal that the El Niño-Southern Oscillation (ENSO) is an important climate mode that impacts monsoon rainfall in Thailand. High-quality proxy records covering recent decades are critically important not only to improve proxy data calibrations but also to provide a better understanding of teleconnections within the modern atmosphere. Preliminary findings demonstrated the potential of tree ring stable isotopes from Thai teak to develop multiproxy climate reconstruction. [ABSTRACT FROM AUTHOR]

Thailand has been regarded as a transition zone between the Indian and western North Pacific monsoons which produce most of the precipitation in this area and sustain large-scale agricultural activities. Their different moisture sources and associated transport trajectories could result in distinguishable seasonal variations in rainfall oxygen isotopes (δ18O). Knowledge about seasonal variability in Thailand monsoon could facilitate agricultural water management and improve our understanding of the Asian monsoon system. In this study, a detailed examination of the intra-seasonal variability of tree-ring cellulose δ18O in teak trees from Northwestern Thailand was performed. The results show clear intra-seasonal variability in cellulose δ18O, with heavier values in the early rainy season and much lighter values in the later rainy season. Climate correlation analysis indicates that there is a significant and positive correlation between sub-seasonal variation in cellulose δ18O and rainfall δ18O. A weak and negative correlation with relative humidity (RH) has also been identified. However, there is no relation between intra-seasonal variation in cellulose and that of the amount of rainfall. These results imply that intra-seasonal variability of cellulose δ18O in teak trees from Northwestern Thailand may inherit such variability in rainfall δ18O and might be slightly shaded by RH. The spatial correlations with large-scale precipitation in the Merged Analysis (CMAP) and Outgoing Longwave Radiation (OLR) data sets indicated seasonal changes in moisture origin and may potentially be used to explore long-term monsoon climate variability on a seasonal scale in subtropical Southeast Asia. [ABSTRACT FROM AUTHOR]

We developed a stable oxygen isotope chronology of tree-ring alpha cellulose (δ18O TR) from archaeological teak (Tectona grandis L.f.) samples from Mae Hong Son (MHS) province, northwestern Thailand. The samples were collected from ancient coffins belonging to the log coffin culture excavated at the Ban Rai rock shelter (BR). The chronology spans a period of 283 years in the late Holocene (AD14–296). The oxygen isotopic composition of BR δ18O TR ranged from 21.15‰ to 26.31‰. Since δ18O TR variations in Thailand teak can be used as indicators for precipitation amount during the rainy summer monsoon season, our chronology can be used as a proxy for regional late Holocene hydroclimate variability. This is confirmed by a significant positive correlation of our BR δ18O TR record with a stalagmite δ18O record from Klang cave, southern Thailand (r = 0.303, p < 0.01). In addition, a REDFIT spectral analysis revealed the existence of multidecadal (26.9-year) and interannual (5.6, 3.4 and 2.8-year) cycles, which may potentially be the fingerprints of climate forcing mechanisms impacting Thailand monsoon precipitation, such as the Pacific Decadal Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO). [ABSTRACT FROM AUTHOR]

• Teak cellulose δ18O values collected from northern Thailand were presented. • Annually resolved δ18O (AD 1871 and 2016) captured entire summer monsoon rainfall. • Monthly resolved δ18O reflected changes in moisture from different Ocean regions. • Cellulose δ18O is modulated by local rain amount and large-scale convection. Thailand is situated in a transition zone of overlap between the Indian monsoon (IM) and the western North Pacific (WNP) monsoon. The region serves as an important area to study the influences of different moisture sources. This study presents the first stable oxygen isotope analysis on seven teak (Tectona grandis Linn.) trees collected from Phrae Province in northern Thailand at different temporal resolutions. Isotopic analyses of teak tree rings at both annual and sub-annual timescales reflected the variations in their source water oxygen isotope ratios (δ18O, i.e., rainfall) to different degrees (Annual scale: r = 0.31, p < 0.05, Monthly scale: r = 0.63, p < 0.01). A 146-year-long annually resolved tree-ring cellulose δ18O series, spanning between AD 1871 and 2016, exhibited moderate negative relationships with both local (r = −0.58, p < 0.01) and regional rainfall amounts, representing the climatology of rainfall totals during the entire summer monsoon period from May to October. A spatial correlation analysis between monthly resolved tree-ring cellulose δ18O with large-scale Climate Prediction Center (CPC), Outgoing Longwave Radiation (OLR), and Merged Analysis of Precipitation (CMAP) datasets, as well as an air mass backward trajectory analysis, indicated that the intraseasonal tree-ring cellulose δ18O values reflected changes in moisture originating from the Indian and Pacific Oceans, rather than the amount of local precipitation. These results imply that variations in northern Thai teak cellulose δ18O values are modulated not only by the local rainfall amount but also by large-scale convection, which varies between different seasons and over time. Advance knowledge of the regional monsoons in the transition area can therefore lead to a broad and complete understanding of the entire Asian monsoon circulation. [ABSTRACT FROM AUTHOR]

Thailand is bounded by the Gulf of Thailand in the Pacific Ocean and the Andaman Sea in the Indian Ocean. Variations in the Thailand monsoon (TM) are strongly influenced by the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) phenomenon. The climatology of Thailand is of great importance for understanding seasonal responses to large-scale climatic variations and associated ocean-atmospheric forcing. This study presents the first longest reconstruction (1792–2016 CE) of March–May relative humidity (RH) based on the tree-ring width chronology of Pinus latteri trees from Nan province, northern Thailand. The growth of P. latteri was mainly limited by pre-monsoon RH variability (r = 0.773, p < 0.001, n = 66). The field spatial correlations with the gridded climate datasets demonstrated that the climatic signals retained in our reconstruction represented regional climate variations. Extremely wet years were observed in 1879, 1887, 1908, 1929, 1942, 1974, and 2013 CE, whereas extremely dry years were found in 1795–1796, 1905, 1960, 1992, and 2010 CE. Spectral analysis and spatial correlation analysis revealed pre-monsoon RH variability in the northern Thailand is linked to large-scale ocean-atmospheric circulations, mainly ENSO and IOD activities due to sea surface temperatures variation in the Pacific and Indian Oceans. ENSO-related climate anomalies during the past 225 years were strongly associated in our reconstruction, of which a total of 63% extremely and abnormally wet years occurred during the La Niña events, whereas 59% of extremely and abnormally dry years corresponded to El Niño events. Our reconstruction indicated increasing extreme wet and dry events since 1900 CE attributed to ENSO activities, and thus provide useful insights to understand occurrence of extreme weather events in Thailand climatology. • We present the first longest reconstruction of March-May relative humidity (RH) between 1792 and 2016 CE. • The reconstruction was based on tree-ring width chronology of Pinus latteri trees. • The radial growth of P. latteri trees was positively (negatively) controlled by the pre-monsoon season RH (VPD/Tmax). • The observed increase in extreme wet and dry events since 1900 CE in our reconstruction were attributed to ENSO activities. • Thailand pre-monsoon RH variability may be linked to large-scale ocean-atmospheric circulations over tropical Indian and Pacific Oceans. [ABSTRACT FROM AUTHOR]