Spring Season in Western Nepal Himalaya is not yet Warming: A 400-Year Temperature Reconstruction Based on Tree-Ring Widths of Himalayan Hemlock (Tsuga dumosa)

Abstract

The Himalayan region has already witnessed profound climate changes detectable in the cryosphere and the hydrological cycle, already resulting in drastic socio-economic impacts. We developed a 619-yea-long tree-ring-width chronology from the central Nepal Himalaya, spanning the period 1399–2017 CE. However, due to low replication of the early part of the chronology, only the section after 1600 CE was used for climate reconstruction. Proxy climate relationships indicate that temperature conditions during spring (March–May) are the main forcing factor for tree growth of Tsuga dumosa at the study site. We developed a robust climate reconstruction model and reconstructed spring temperatures for the period 1600–2017 CE. Our reconstruction showed cooler conditions during 1658–1681 CE, 1705–1722 CE, 1753–1773 CE, 1796–1874 CE, 1900–1936 CE, and 1973 CE. Periods with comparably warmer conditions occurred in 1600–1625 CE, 1633–1657 CE, 1682–1704 CE, 1740–1752 CE, 1779–1795 CE, 1936–1945 CE, 1956–1972 CE, and at the beginning of the 21st century. Tropical volcanic eruptions showed only a sporadic impact on the reconstructed temperature. Also, no consistent temperature trend was evident since 1600 CE. Our temperature reconstruction showed positive teleconnections with March–May averaged gridded temperature data for far west Nepal and adjacent areas in Northwest India and on the Southwest Tibetan plateau. We found spectral periodicities of 2.75–4 and 40–65 years frequencies in our temperature reconstruction, indicating that past climate variability in central Nepal might have been influenced by large-scale climate modes, like the Atlantic Multi-decadal Oscillation, the North Atlantic Oscillation, and the El Niño-Southern Oscillation.

Tree-Ring Isotopic Records Suggest Seasonal Importance of Moisture Dynamics Over Glacial Valleys of the Central Himalaya

“…Moreover, we comprehend that the reported decline in pre-monsoon surface temperature since the 1960s (Yadav et al, 2004) and concurrent increasing trend in pre-monsoon precipitation could be a consequence of evaporative cooling associated with regional vegetation greening (Shen et al, 2015). Multi-century temperature reconstructions from the adjacent western Nepal Himalayan region have also indicated that there is no increase in pre-monsoon temperature trends (Thapa et al, 2015;Aryal et al, 2020).…”

Retreating Glacier and Advancing Forest Over the Past 200 Years in the Central Himalayas

“…Similarly, some glacier‐fluctuation episodes from the Gawalong glacier (1768, 1918) (Zhu et al, 2013), Lhamkoka glacier (1777, 1918), Gyalaperi glacier (1763) (Bräuning, 2006), Xinpu glacier (1746, 1927), Gongpu glacier (1910), Zepu glacier (1785), and Baitong glacier (1757) (Hochreuther et al, 2015) in the southestern Tibetan Plateau were closely synchronized with our moraine dating in the Manang valley in the central Himalayas. Furthermore, the periods with advancing glacier corresponded with cold intervals (1796–1874 and 1900–1936), as shown by tree ring‐based spring temperature reconstruction from the lower part of the Manang valley (Aryal et al, 2020), and from the southestern Tibetan Plateau (1892–1927 and 1958–1981) (Huang et al, 2019). The synchronization between ages of the dated moraines and higher snow accumulation epochs (Figure 6) implied that higher snow accumulation period may link with formation of moraines.…”

“…It has been successfully used to date moraines in the southeastern Tibetan Plateau (Bräuning, 2006; Hochreuther et al, 2015; Xu et al, 2012; Zhu et al, 2013), southern Chile (Koch & Kilian, 2005), Canadian Rocky Mountains (Luckman, 1993; Smith et al, 1995), European Alps (Holzhauser et al, 2005; Reinig et al, 2018), and Patagonian Andes (Masiokas et al, 2010; Meier et al, 2019). Most dendrochronological studies in the central Himalayas focused on tree growth responses to climate change or past climate reconstructions (Aryal et al, 2020; Cook et al, 2003; Liang et al, 2014, 2019; Panthi et al, 2020; Rai et al, 2019; Sano et al, 2005; Sigdel, Dawadi, et al, 2018; Thapa et al, 2015) or treeline dynamics (Sigdel, Wang, et al, 2018; Sigdel, Liang, et al, 2020). In spite of the dense forest cover observed on the LIA glacial deposits, little is known whether dendrochronology can be used to reconstruct glacier fluctuation events in the Himalayas.…”

INTRAGRO: A machine learning approach to predict future growth of trees under climate change

“…In our study site, the MI is positive in the monsoon season in both future periods, meaning precipitation exceeds PET. Therefore, enhanced growth during the summer monsoon will likely be controlled by temperatures instead of rainfall, as evidenced by other studies (eg., Aryal et al., 2023; Aryal, Gaire, et al., 2020). As discussed above, cool and moist weather conditions encourage the occurrence of cluster1, significantly increasing the growth rate, especially in July and August.…”