Dendroclimatic Reconstruction of Mean Annual Temperatures over Treeline Regions of Northern Bhutan Himalayas

Abstract

The Himalayan region is likely particularly exposed to climate change indicated by the high regional rate of change. The number of high-resolution, well-calibrated, and long-term paleoclimate reconstructions are however regrettably few, to set this change in a longer-term context. The dendroclimatic reconstructions over Himalaya that do exist have only reconstructed summer season temperatures, and rarely or never attempted to reconstruct mean annual temperatures. The paucity of long meteorological records is a matter of concern when developing chronologies of climate sensitive tree-ring data in Bhutan, but the chronologies would theoretically be of high potential for extending short meteorological records back in time using trees in high-elevation ecotones. The objectives of this study were to explore dendroclimatic signals in tree-ring width chronologies of Abies densa growing in these extreme ecotones and to reconstruct, if possible, annual temperatures over Northern Bhutan. A point-by-point regression analysis revealed that the regional composite chronology was significantly and positively correlated with temperatures of all months of the current year, i.e., January to December. The chronology was highly correlated with annual temperatures (calibration period R = 0.67 and validation period R = 0.50; p < 0.001) allowing a reconstruction of temperature over Northern Bhutan (NB-TEMR). The NB-TEMR reveals some common variations with summer temperature reconstructions of the Northern Hemisphere as well as the Himalayan region, particularly w.r.t to the recent warming trend. The reconstruction covers the period of 1765 to 2017. This reconstruction reveals a warming trend since 1850 with higher rates of warming 1935 to 2017, but with a pause around 1940–1970. The warming is consistent with reduced volcanic activity and increase of greenhouse gases. We anticipate that our new reconstruction of annual mean temperature could be an important contribution for future climate change studies and assessments of climate models.

A Review of the Current State and Future Prospects of Dendrochronological Research in Bhutan

“…2022). Only a few studies were conducted from locations above the tree line (Sano et al 2013; Khandu et al 2022a,b), and few studies in the south-central broadleaved forest (Nado 2013; Tenzin et al . 2017; Nidup 2021).…”

“…2017; Wangchuk et al . 2018; Penjor 2019; Khandu 2022). Climate science and research in Bhutan face significant challenges compared to other countries.…”

“…2019). Tree rings are considered one of the most reliable proxies of past climate and have been widely used in reconstructing past temperatures and precipitation (Bhattacharyya and Shah 2009; Khandu et al . 2022a,b), drought (Seim et al 2016), and forest fire history (Tenzin et al .…”

Tree-ring hydrological research in the Himalaya: State of the art and future directions

“…Despite the occurrence of a wide variety of taxa suited to dendrochronology (e.g. Larix griffithiana, Tsuga dumosa, Abies densa, Juniperus indica, Pinus wallichiana ), only a few have been used for the reconstruction of temperature (Aryal et al, 2020; Bhattacharyya and Chaudhary, 2003; Borgaonkar et al, 2018; Chaudhary and Bhattacharyya, 2000; Chaudhary et al, 1999; Gaire et al, 2023; Khandu et al, 2022; Krusic et al, 2015; Yadava et al, 2015) and precipitation (Khan et al, 2020; Sano et al, 2013; Shah, 2018; Singh et al, 2021; Yadav, 2011; Yadav et al, 2014) across the Himalaya (Figure 1). The same is the case for hydrological reconstructions such as streamflow (Cook et al, 2013; Gaire et al, 2022; Misra et al, 2015; Rao et al, 2020; Shah et al, 2013, 2014; Singh and Yadav, 2013).…”

Increasing growth sensitivity of Pinus wallichiana to summer season maximum temperature – evidence from central Bhutan Himalaya

“…Sano et al (2013) reconstructed 269-year summer monsoon precipitation using stable oxygen isotopes from tree rings of Larix griffithii. Multi-centennial temperature reconstructions have also been developed from the region using tree-ring width chronologies of Picea spinulosa (Krusic et al, 2015) and Abies densa (Khandu, Polthanee, & Ayutthaya, 2022b). Advancing tree lines have recently been reported in the northern extreme of Bhutan based on observations of regeneration and expansion rates of Abies densa (Khandu, Polthanee, & Ayutthaya, 2022a).…”