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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.

To study the long-term hydroclimate variability in the Satluj Basin, streamflow data was reconstructed using tree-ring width datasets from multiple taxa available from the Kullu Valley, western (Indian) Himalaya. Five ring-width tree-ring chronologies of three conifer tree taxa (Abies pindrow, Cedrus deodara, and Pinus roxburghii) significantly correlate with the streamflow during the southwest monsoon season. Based on this correlation, a 228-year (1787–2014 CE) June–August streamflow was reconstructed using average tree-ring chronology. The reconstruction accounts for 34.5% of the total variance of the gauge records from 1964 to 2011 CE. The annual reconstruction showed above-average high-flow periods during the periods 1808–1811, 1823–1827, 1833–1837, 1860–1863, 1876–1881, and 1986–1992 CE and below-average low-flow periods during the periods 1792–1798, 1817–1820, 1828–1832, 1853–1856, 1867–1870, 1944–1947, and 1959–1962 CE. Furthermore, a period of prominent prolonged below-average discharge in the low-frequency streamflow record is indicated during the periods 1788–1807, 1999–2011, 1966–1977, 1939–1949, and 1854–1864. The low-flow (dry periods) observed in the present streamflow reconstruction are coherent with other hydroclimatic reconstructions carried out from the local (Himachal Pradesh and Kashmir Himalaya) to the regional (Hindukush mountain range in Pakistan) level. The reconstruction shows occurrences of short (2.0–2.8 and 4.8–8.3 years) to medium (12.5 years) periodicities, which signify their teleconnections with large-scale climate variations such as the El Niño–Southern Oscillation and the Pacific Decadal Oscillation.

A regional, 175 year long, tree-ring width chronology (spanning 1840–2014 C.E.) was developed for Pinus wallichiana A. B. Jacks. (Himalayan Blue pine) from the Lidder Valley, Kashmir, Northwest Himalaya. Simple and seasonal correlation analysis (SEASCORR) with monthly climate records demonstrates a significant direct positive relationship of tree growth with winter temperature. A linear regression model explains 64% of the total variance of the winter temperature and is used to reconstruct December–March temperatures back to 1855 C.E. The most noticeable feature of the reconstruction is a marked warming trend beginning in the late twentieth century and persisting through the present. This reconstruction was compared with instrumental records and other proxy based local and regional temperature reconstructions and generally agrees with the tree-ring records and is consistent with the marked loss of glacial ice over the last few decades. Spectral analysis reveals a periodicity likely associated with the Atlantic Multidecadal Oscillation and El Niño–Southern Oscillation. Spatial correlation patterns of sea surface temperatures with the observed and reconstructed winter temperatures are consistent with larger scale warming in the region.

The sediment deposits of northwestern Tripura, northeast India, revealed the enhanced proximity to the marginal marine environments, forest cover variations and anthropogenic influences. We infer the palaeo-vegetation and palaeo-environmental conditions between 9900 and 1800 cal B.P. through a 1.80 m deep sediment profile, from the remote location of Charilam, Tripura, using biotic (fossil pollen) and abiotic (mineral magnetism) proxies. The sediment profile recorded warm and humid conditions between 8300 and 6200 cal B.P., which later shifted towards less humid phase until 4900 cal B.P. The lower part of the sediment profile provided evidence of enhanced sea-level in this region, as manifested by mangrove taxa found between 9900 and 4900 cal B.P. But later, these taxa were minimal and thereafter, diminished in the sediments during the Late Holocene (4100–1800 cal B.P.).The occurrence of fewer tree taxa and dominance of larger grass pollen signify the enhancement of anthropogenic activities in the region, during the recent times. The shifts in mineral magnetic content towards fine-grained anti-ferrimagnetic hematite components, as exhibited by relatively high Hard IRM, SIRM/ΧLF, ARM/SIRM ratio and low S–ratio towards the end of the Middle Holocene, resonate with the climate variations concurrent to the vegetation changes. These interpretations lead to the perception of a reduction in the Indian Summer Monsoon (ISM) strength during the Late Middle Holocene. The inception of anthropogenic activities has also induced the changes in the vegetation cover, leading to increased soil erosion and land-use changes during the Late Holocene in the region, which are well observed in the pollen and mineral magnetic records. This study focuses on multi-proxy analyses of the Holocene sediments in this part of northeast India, which has no such previous records.

Key messageWe propose an improved exponential equation for the nonlinear dependence of cell measurements on the seasonal cell production in conifer wood. These changes shall simplify the model towards ease in understanding, interpretation and analysis.With methodological development, quantitative parameters of wood cellular structure have featured as dendroclimatic indicators in various studies. But to disentangle climatic impacts in different wood anatomical characteristics, relationships between them have to be described quantitatively and extricated. This study investigates exponential description of the non-linear dependences of conifer wood cell measurements on their seasonal production in cambial zone. Improvement to the equation of exponential model was suggested, simplifying the interpretation and analysis and providing biological meaning to all numerical parameters of the model. This new equation was demonstrated for 630 tree rings from 20 to 40-year-old trees of Siberian spruce (Picea obovata Ledeb.) in Siberia, collected at the experimental plantation, as well as for its subsets from plots of various planting density, demonstrating plausible value of the new proposed numerical parameter of model and dependence of the other parameter on the stand density, probably based on the tree height. Limitation for successful fitting of this exponential model was demonstrated, based on representativity of wide and narrow rings within sample; we proposed possible way to overcome it in certain cases.

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.

Key MessageThe principal components of tree-ring anatomical chronologies of Scots pine proved to be much better proxy than its tree-ring width for reconstruction of climate-driven component in the regional yield of cereals Tree-ring records are often used as a proxy not only for climate, but also for other related variables. One of such applications is the reconstruction of crop yield, since both are indicators of productivity in the respective ecosystems. Recently, finer parameters of wood structure were applied to enhance the sensitivity and temporal resolution of the registered climatic signal and thus to improve the quality of tree-ring based reconstructions. This pioneering study tests cell-scale quantitative wood anatomy (QWA) of conifer tree species as a proxy for crop yield in the moisture-limited plains of Khakassia (South Siberia). Spring wheat, oats, and barley yield series generalized for rain-fed (north of the region) and irrigated (central part) fields in the steppes were compared with long-term (1807–2018) QWA series of the Scots pine (Pinus sylvestris L.) from the forest-steppe in the foothills. Chronologies of the cell radial diameter and cell wall thickness, describing the tree ring separated into 15 sectors, were obtained and indexed to remove their common exponential dependence on the number of cells per radial row in the ring. The tree-ring width alone could explain only 16.0 and 5.3% of yield variation for rain-fed and irrigated crops, respectively. Whereas, the multifactor linear regressions with stepwise inclusion of QWA chronologies explained 48.4 and 16.1%. The implementation of principal components for QWA in the models further increased the fitness to 48.9 and 23.0%. These reconstructions have climatic responses during the vegetative season similar to ones of the respective actual yield series. The reconstructed history of the low-yield years is supported by documented evidence of crop failures, droughts, and other related events.

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.

Improvement of dendrochronological crops yield reconstruction by separate application of earlywood and latewood width chronologies succeeded in rain-fed semiarid region. (1) Background: Tree-ring width chronologies have been successfully applied for crops yield reconstruction models. We propose application of separated earlywood and latewood width chronologies as possible predictors improving the fitness of reconstruction models. (2) Methods: The generalized yield series of main crops (spring wheat, spring barley, oats) were investigated in rain-fed and irrigated areas in semiarid steppes of South Siberia. Chronologies of earlywood, latewood, and total ring width of Siberian larch (Larix sibirica Ledeb.) growing in forest-steppe in the middle of the study area were tested as predictors of yield reconstruction models. (3) Results: In the rain-fed territory, separation of earlywood and latewood allowed increasing variation of yield explained by reconstruction model from 17.4 to 20.5%, whereas total climatic-driven component of variation was 41.5%. However, both tree-ring based models explained only 7.7% of yield variation in the irrigated territory (climate inclusion increased it to 34.8%). Low temperature sensitivity of larch growth was the main limitation of the model. A 240-year (1780–2019) history of crop failures and yield variation dynamics were estimated from the actual data and the best reconstruction model. (4) Conclusions: Presently in the study region, breeding of the environment-resistant crops varieties compensates the increase of temperature in the yield dynamics, preventing severe harvest losses. Tree-ring based reconstructions may help to understand and forecast response of the crops to the climatic variability, and also the probability of crop failures, particularly in the rain-fed territories.