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The high-resolution temporal records (1738–2018 CE) of the dendrochronological analysis on Cedrus deodara from Uttarakhand and Himachal Pradesh in the western Himalayan region were generated. An analysis of the association between the Normalized Difference Vegetation Index (NDVI) and tree-ring radial growth indicated a significant positive relationship from April to July. The association between tree rings and other hydroclimatic variables was used to further evaluate this relationship. Based on the observation, mean April–July NDVI variability since 1790 CE was reconstructed based on the regional tree-ring chronology. Comparisons of the reconstructed NDVI with gridded precipitation, drought records, and proxy-based hydroclimatic reconstructions revealed a consistent agreement over a large spatial domain extending beyond the study region. We observed a correlation between the region's NDVI browning (reduction) and past droughts and famines. Comparison has been made to the regional proxy-based hydroclimatic reconstruction and stable oxygen isotope datasets with the present NDVI reconstruction. This revealed the commonalities in the regional hydroclimatic scenario recorded in these data sets over the last few centuries. This first tree-ring-based NDVI reconstruction from the western Himalayas infers regional climate-vegetation dynamics during the past two centuries. This reconstruction provides valuable input for modeling vegetation dynamics for predicting vegetation changes due to climate variations in the western Himalaya. [ABSTRACT FROM AUTHOR]

The Late Holocene fossil pollen records from the Zemu glacier, located in Yabuk, North Sikkim, in the eastern Himalayas, effectively generated quantitative climate reconstructions based on the transfer function model. The transfer function model was developed by establishing a modern pollen–climate calibration set from the temperate alpine belt of North Sikkim. A redundancy analysis was carried out to detect the pattern of variation of climatic variables in the modern pollen datasets. The mean annual precipitation (MAP) and mean temperature of the warming month (MTWA) had the strongest influence on the composition of the modern pollen samples among the climatic variables considered in the analysis. Proxy data in the form of fossil pollen records were analyzed for reconstructing past climate based upon the relationships between modern pollen vegetation assemblages and climatic patterns. Transfer functions for MAP and MTWA were developed with the partial least squares (PLS) approach, and model performance was assessed using leave-one-out cross-validation. The validated model was used to reconstruct MAP and MTWA for the last 2992 cal years BP (1042 BC) in North Sikkim. The variability observed in the reconstructions was analyzed for past global climatic events. It was further compared with the available regional and hemispheric proxy-based climate reconstructions. The reconstructions captured comparable Medieval Warm Period (MWP) and Little Ice Age (LIA)-like events from the Zemu glacier region. The fossil pollen data and climate reconstructions were further compared with the mineral magnetism data of the subsurface sediment profile. [ABSTRACT FROM AUTHOR]

We reconstructed summer (June–September) minimum temperature for eastern Nepal over the past 288 years (1733–2020 CE), using a total tree-ring width chronology of Himalayan Larch (Larix griffithiana (Lindl. and Gord.)) from Kanchanjunga Conservation Area (KCA). This study is the first minimum temperature reconstruction for the eastern Himalaya region of Nepal. We examined the response of the Larix ring-width chronology to different climate variables including precipitation, and minimum, maximum and mean temperatures. Of all climatic variables, minimum temperature has the strongest correlation with tree-ring chronology. This response revealed that the growth of the L. griffithiana is limited by temperature-induced physiological behaviors during summer season. The reconstruction shows fluctuating warm and cool periods during the entire period and captures warming during recent decades. This increasing warming trend appears to be unprecedented in the context of the past 288 years. We observed short (2.5 years) and multidecadal (35, 43, 71 and 100 years) cyclicity, which suggests possible atmospheric teleconnection with the broader circulation system of Atlantic Multidecadal Oscillation (AMO). This possible teleconnection is further revealed in spatial field correlation and also supported by temporal comparison of the reconstruction with instrumental- and proxy-based AMO records. [ABSTRACT FROM AUTHOR]

Tree rings are widely used to reconstruct past climates in regions where observational records of climate are short. In this study, we developed a 294 years-long (1718–2011 CE) ring-width chronology of the Himalayan Silver fir (Abies spectabilis (D.Don, Spach)) from Humla district in western Nepal to reconstruct winter minimum temperature for the remote region of central Himalaya where instrumental records are limited to past three or four decades. Ring-width chronology of the Himalayan Silver fir showed strongest and significant positive correlation with minimum winter temperature prior to the growing season. Based on this relationship, we reconstructed the winter season (previous October–current February) minimum temperature for western Nepal covering the period of 1780–2008 CE. Our reconstruction showed that winter minimum temperature is continuously increasing since the early twentieth century with unprecedented rapid warming in the latter half. The cold episodes in the reconstruction coincided with the major volcanic eruptions in the Northern Hemisphere and tropical regions. The spectral analysis using Multi-Taper Method revealed that the winter temperature in the north-western Himalaya has short- to medium-term periodicities of 2–3, 5.8–6.2, 7.9–8.2, 39–46 and 56–73 years, which suggest possible teleconnections with ENSO (El-Nino Southern Oscillation) and AMO (Atlantic Multidecadal Oscillation). [ABSTRACT FROM AUTHOR]

Western Nepal has experienced a severe drought in the past two decades, but observation records across Nepal are too short to place the recent drought in a longer context to understand the full range of natural variability in the climate system. In the present study we have collected tree core samples of Tsuga dumosa from two sites, Chhetti and Ranghadi, in the Api Nampa Conservation Area of the western Nepal Himalayas to understand drought variation for the past three centuries. We have developed a 357-year (AD 1657-2013) tree-ring chronology. The tree growth-climate response analysis revealed a stronger positive correlation with spring (March-May) standardized precipitation evapotranspiration index (SPEI01) (r = 0.523, p < 0.01) than precipitation (r = 0.459, p < 0.01), self-calibrating Palmer drought severity index (scPDSI) (r = 0.250, p < 0.01), or temperature (r = -0.486, p < 0.01). Stronger positive correlation with SPEI01 indicates moisture availability is the limiting factor for the growth of this species on these sites. Based on this growth-climate response we reconstructed spring SPEI from AD 1707 to 2013 for the region. The reconstruction showed several dry and wet episodes indicating no persistent climate trend within the past three centuries. The current drought is one of the four most severe in our 307-year record. [ABSTRACT FROM AUTHOR]

Climate driven changes have impacted various civilizations and have major influence on human population globally. Remote regions such as the Himalaya also archived these climatic events in various proxies. The Eastern Himalaya region has recorded the Holocene climate change events in numerous proxy records. A multi–proxy record of the early to late–mid Holocene climate change from the catchment of PankangTeng Tso (PT Tso) Lake at an altitude of 3935 m asl in the Tawang district of Arunachal Pradesh was studied. A 90 cm sediment profile showed a synchronous pattern of Holocene climate changes in the palynological, environmental magnetic and carbon isotope data recorded. Dominant cold-humid conditions at 4625 cal yr BP followed by a cold-dry period was documented in the proxy data. The vegetation vis–à–vis climate varied throughout the Holocene and cold–dry conditions along with sub-alpine vegetation prevailed in the region around the "4.2ka event". Human activities and environmental changes in the Tawang district during the Holocene probably impacted the vegetation during this significant period of the development and demise of major global civilizations. [ABSTRACT FROM AUTHOR]

ABSTRACT: A reconstruction of annual to multi‐decadal precipitation based on ring‐width of Cedrus deodara (Himalayan cedar or deodar) was carried out in the Lidder (Liddar) Valley, Kashmir Himalaya. A composite tree‐ring chronology demonstrated a significant direct relationship with April–June precipitation. A modified version of point‐by‐point regression methodology was used to reconstruct April–June precipitation since 1723 C.E. This reconstruction accounts for 40% of the total variance of the actual precipitation in the calibration period. The reconstruction shows a prolonged decadal dry period between 1822 and 1887 C.E., the driest period in the reconstruction. The wettest period occurred during the early 19th century and latter part of the 20th century. Extreme dry and wet events have been identified in the reconstruction on the basis of percentile distribution. The reconstruction was compared with documented extreme flood, famines and drought events in Kashmir Valley occurring in those 288 years. The composite 500 mb height‐anomaly maps suggest the prospect to study the long‐term atmospheric circulation variability over the Kashmir Valley and surrounding region using tree‐ring data. The impact of westerlies in the precipitation patterns was also evident in analysis of composite 500 mb height anomaly. Furthermore, the reconstruction was validated through comparison with independent records and spatial correlation with gridded precipitation and drought. [ABSTRACT FROM AUTHOR]

The precipitation in the Kumaun-Gharwal (Uttarakhand) Himalaya (KGH) is predominantly regulated by the Indian summer monsoon (ISM) and has been declining over the last century. However, because of limited historical data, it is difficult to place this recent decreasing trend in the context of pre-anthropogenic influences and understand a fuller range of hydroclimate scenarios for the region. Thus, we developed a 508-year regional tree-ring stable oxygen isotope (δ18O TR) record for multiple coniferous taxa (Abies spectabilis , Cedrus deodara and Picea smithiana) for the KGH, which spanned 1508–2015 CE. The δ18O TR record explained 35.8% of instrumental June–August Palmer Drought Severity Index (JJA PDSI) variance modelled from a nearby meteorological station. The JJA PDSI reconstruction shows regional coherency with both instrumental and proxy-based independent hydroclimatic records providing confidence that it is a reliable proxy to assess the long term hydroclimatic variability of the region. We identified decreasing strength of JJA PDSI reconstruction in KGH during recent decades indicating intensified drought. This is in the context of pre-anthropogenic influences and understand a fuller range of hydroclimate scenarios for the region. The δ18O TR also has coherency with Pacific and Indian Ocean sea surface temperature variability illustrating the broader teleconnections that influence the regional hydroclimate. • The strength of the Indian Summer monsoon has declined in the high altitude regions of the Kumaun-Gharwal Himalaya (KGH). • Tree-ring stable oxygen isotope record (δ18OTR) of multiple conifer taxa established a 508-year long regional chronology. • JJA PDSI reconstruction was carried out and revealed past droughts in the KGH. • These past droughts during the recent decades have similar intensity as the past drought in the early part of the record. • The δ18OTR regional record has teleconnections with SST in the Pacific and Indian Ocean. [ABSTRACT FROM AUTHOR]

We developed a new, 422-year long tree-ring width chronology (spanning AD 1591-2012) from Picea smithiana (Wall.) Boiss in Khaptad National Park, which is located in the far-western Nepalese Himalaya. Seasonal correlation analysis revealed significant indirect relationship with spring temperature and lead to the reconstruction of March-May average temperature for the past 373 years (AD 1640-2012). The reconstruction was found significant based on validation statistics commonly used in tree-ring based climate reconstruction. Furthermore, it was validated through spatial correlation with gridded temperature data. This temperature reconstruction identified several periods of warming and cooling. The reconstruction did not show the significant pattern of cooling during the Little Ice Age but there were few cold episodes recorded. The spring temperature revealed relationship with different Sea Surface Temperature index over the equatorial Pacific Ocean, which showed linkages with climatic variability in a global scale. [ABSTRACT FROM AUTHOR]

Abstract: Tree-ring data of Cedrus deodara (Deodar) growing within the Beas river basin, Kullu valley, Himachal Pradesh in western Himalaya, have been analyzed in relation to streamflow reconstruction. The correlation between Deodar tree-ring chronology and river discharge data from various gauge stations of the Beas river basin showed positive relationships with early summer months (March–April). Streamflow of these months has been reconstructed using a simple linear regression transfer function model which goes back to AD 1834. Explained variances during the calibration period are 43.7% and 60.6% for two gauge stations, Bhuntar and Thalout, respectively. In the reconstructed data (AD 1834–1984) the periods of highest streamflow were during AD 1840–1843, 1893–1897, 1922–1926, 1935–1940 and 1942–45; and lowest were during the years AD 1847–1851, 1863–66, 1927–1929, 1960–1962 and 1972–1974. Spatial coherence analysis between the reconstructed series with regional gridded precipitation and nearby longest instrumental precipitation records showed coincidence with drought and wet periods. Through the spatial correlation analysis between reconstructed March–April runoff and gridded Palmer Drought Severity Index (PDSI), a common regional moisture variation was identified. [Copyright &y& Elsevier]

Abstract: This research aimed to evaluate spatio-temporal growth variability of three Pinus species viz. Pinus kesiya (Khasi pine), Pinus merkusii (Merkus pine) and Pinus wallichiana (Blue pine) along with the existence of species differentiation among the taxa in northeast India. Several statistical analyses were used, namely Pearson correlation and multivariate approaches involving UPGMA Cluster Analysis; ordination methods by Principal Component Analysis (PCA) and Non-metric multidimensional scaling (NMDS) on tree-ring width chronologies from 13 sites. The tree growth-climate relationships were assessed with both correlation and bootstrap response function using regional climate datasets of each sampling site prepared by averaging the nearest grid points of 0.5×0.5° of CRU TS-2.1 climate dataset. Pronounced species differentiation in the growth pattern among the three Pinus taxa was inferred. The observed spatio-temporal variability revealed inter-species tree growth variations were not uniform suggesting no common factor influenced the radial tree growth in this region, which may be related to anthropogenic impact or non-climatic factors. The tree growth-climate relationship showed that climatic factors limiting the radial growth of Pine are mostly similar for intra-species but diverse in inter-species. This study is extremely relevant in terms of species and site selection for the long-term climate reconstruction and forest management in the Northeast Himalaya. [Copyright &y& Elsevier]

Abstract Knowledge of the long-term frequency and intensity of drought events in an area is crucial since drought has adverse effects on natural ecosystems, food security, economy, society, and civilization. We developed a 405-year long (1611–2015C.E.) tree-ring chronology of Pinus wallichiana (Blue pine) from the Dolpo area of the trans–Himalayan region in Nepal to reconstruct drought variability in this remote region. Correlation analysis revealed significant positive relationships with February–August precipitation, but negative correlations with temperature. High positive correlations with the self-calibrated Palmer drought severity index (scPDSI) confirmed that moisture availability during the early growing season and full growing season is the primary limiting factor for Blue pine tree growth in the trans–Himalayan region. We used a linear regression model between our tree-ring record and regional climate data to reconstruct a 319-year long (1697–2015C.E.) February–August scPDSI series. This reconstruction accounts for 39.4% of the total variance in actual scPDSI over the calibration period (1957–2015C.E.). The reconstruction showed that the area was under slightly dry conditions for most of the reconstructed period, with below normal scPDSI values. An extreme drought was observed in the year 1707. Also, the years 1705, 1706, 1784, 1786, 1809, 1810, 1813, 1821, 1849, 1858, 1861, 1909, 1967, 2006, and 2009 experienced severe drought conditions. Consecutive years with moderate drought were 1702–1706, 1783–1789, 1796–1798, 1812–1814, 1816–1827, 1846–1848, 1856–1864, 1873–1877, 1879–1882, 1899–1901, 1908–1911, and 1967–1968. Three historic mega-drought events that occurred in Asia were also captured in our reconstruction: Strange Parallels drought (1756–1768), the East India drought (1790–1796), and the late Victorian Great Drought (1876–1878). Very few wet years (1776–1979, 1989, 1991, and 2003) were observed during the reconstruction period. Power spectrum analysis revealed drought variability at frequencies of 2.0–2.5, 3.0, 12.0, and 128 years, suggesting that drought in the region might be linked to broad-scale atmospheric-oceanic variabilities such as the El Niño-Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO). The results not only improve our understanding on regional drought variability, but are also helpful to make decisions on adaptation measures for protecting the marginal communities of the trans–Himalayan region from the anticipated adverse impacts of future droughts. Highlights • Radial growth of Pinus wallichiana is mainly limited by moisture availability. • February-August scPDSI during 1697–2015 C.E. was reconstructed for trans-Himalaya region • The trans-Himalayan region experienced prolonged drought during 19th and 20th century. • Drought variability in the trans-Himalayan regions has teleconnections with ENSO and AMO. [ABSTRACT FROM AUTHOR]

Vegetation and climate during later part of Late Pleistocene have been reconstructed from Ziro valley, Arunachal Pradesh, Eastern Himalaya based on pollen data along with carbon isotope and magnetic susceptibility data The study reveals that the area and the vicinity is occupied by mixed broad leaved – conifer forest and pine grass savanah at variable densities at least since 66,000yr BP. The phases of expansions and declines of Oaks with decline and increase of Pines and grasses probably occurred under increase (warm–moist) and decrease (cool–dry) of S.W. monsoon precipitation respectively. The increasing trend of S.W. monsoon and temperature is recorded during ∼44,000 to 34,000 cal yr BP synchronizing with the peat development, and which peaked at around 35,000 cal yr BP. This may link to the interstadial phase during the last major glacial cycle in the Himalayan region. It is also reflected in the decline of δ 13 C value indicating dominance of C-3 type of vegetation. The increased values of χFD%, and lower values χLF magnetic susceptibility, recorded during the phase of the peat deposit, further advocate's higher monsoon intensity. Impact of expansion of glacier felt with peak (LGM) around 20,000 cal yr BP is perceived. Tree line had moved to lower altitudes due to increased aridity and low temperature. During this time existence of savannah type of vegetation is also evident by the increase of C4 taxa. Decreased FD% and increased χLF susceptibility also indicate reduced S.W. monsoon intensity. [ABSTRACT FROM AUTHOR]

An exploratory pollen and carbon isotopic study carried out from a 1 m deep sediment profile at the Paradise Lake (4176 m amsl) near Sela Pass has revealed vegetation vis-à-vis climatic changes during Late Holocene. Around 1800 yrs BP (around AD 240), conifer-broadleaved forest used to grow in the vicinity of the study site under warm and moist climate, similar to the prevailing present-day conditions which turned out to be comparatively more warmer 1100 yrs BP (around AD 985) corresponding to the Medieval Warm Period. The glaciers seem to have receded and tree line might have been closer to the site. Around 550 yrs BP (around AD 1400) decrease in Tsuga, Juniperus and Quercus suggests a trend towards comparatively cooler and less moist climate corresponding to the Little Ice Age. This is followed by an amelioration of climate more or less equivalent to the present day. Carbon isotopic analyses in sediments at different intervals reveal fluctuation of C-3 taxa dominantly throughout under variable moist climatic regime. [ABSTRACT FROM AUTHOR]

• Tree growth in the Karnali river catchment was sensitive to moisture availability. • March–July streamflow was reconstructed for Karnali River Basin since 1628 CE. • An increasing frequency of extreme events was found during the recent decades. • Streamflow variability of the Karnali river is mainly linked with ENSO and PDO. The Karnali River is one of the major transboundary rivers of the Nepalese central Himalaya and a major tributary of the Ganges River. In order to investigate regional historical hydroclimate variability, we compiled eleven tree ring-width chronologies based on 354 exactly dated tree cores from five coniferous species for the Karnali River catchment. The chronologies were moisture-sensitive and the composite chronology was significantly correlated with spring-to-early summer (March–July) (R = 0.67, P < 0.001) discharge at the Chisapani gauging station. The robust calibration (R2 = 0.45, 1962–2010) enabled us to reconstruct March–July streamflow variability of Karnali River Basin (KRB) over the past four centuries. The streamflow reconstruction showed prolonged pluvial periods during 1650–1661, 1711–1718, 1723–1731, 1824–1831, 1877–1889, 1924–1931, and 1971–1981, while prolonged low-flow periods occurred during 1639–1649, 1689–1710, 1753–1769, 1777–1784, 1803–1823, 1867–1876, 1942–1959, and 1963–1970. Our reconstructed March–July streamflow series correlated positively with the seasonally averaged drought index and precipitation in the central-west Himalayan region and vicinities. The streamflow reconstruction revealed an increasing frequency of extreme low-flow and pluvial events in the central-west Himalayan region, especially during the past century. We found short (2.1–3.3, 6.2–6.3, and 8.5–8.7 years) to medium (12.2–12.5 years) periodicities in the reconstructed streamflow series, implying teleconnections with broad-scale climate modes like the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Our Karnali River streamflow reconstruction represents an update of regional hydroclimate variability, which may serve as a useful reference for water resource management and appropriate water-use policies in the context of current and future climate change. [ABSTRACT FROM AUTHOR]