Long-term climate records which help decipher past climate variability and its impact are scarce in the tough terrain of the Himalayan region. Therefore, in order to fill the climate data gap and understand the glacier climate linkage, we developed a 231 year long (1785–2015 CE) March–June temperature record using ring-width chronology of Himalayan fir (Abies pindrow (Royle ex D.Don) Royle) for the Din Gad valley, Dokriani glacier region, Uttarkashi, Uttarakhand, in the Western Himalaya. The Din Gad, originating from the Dokriani glacier, is a meltwater river contributing to Bhagirathi catchment in the headwaters of the socio-economically vital Ganga River. The 21-year running mean of the temperature record showed 1978–1998 CE as the coldest period followed by 1925–1945 CE, and 1890–1910 CE as the warmest period followed by 1946–1966 CE over the entire time series. The reconstruction matches well with tree-ring based temperature records available from the Garhwal Himalaya. It also shows similarity to tree-ring based temperature reconstructions from the Western Himalaya, Nepal, Tibetan Plateau and Bhutan, thus displaying a regional scale climate signal. The low frequency fluctuation patterns of the March–June temperature also matches with Asia and Northern hemisphere temperature records. Reconstructed March–June temperature record showed a statistically negligible warming temperature trend during 1901–1989 CE in the 20th century. It, however, captured a warming spike from 1990s CE which continues rising into the 21st century, which is also evident in the Northern hemisphere temperature record. Moreover, temperature rise is not anomalous in the past 231 years and well within range of the rest of the series. The present temperature record exclusively from the glacier region revealed a strong linkage with the benchmark Dokriani glacier's winter mass balance (November–April) revealing mass loss (gain) episodes occurred in warm (cool) phases. This first such record from the glacier valleys in Ganga headwaters would be of great value at providing insight into past climate variability and glacier behaviour with respect to climate change in long term perspective, and thus would provide valuable information for water resource management in light of climate change.

Warming-induced expansion in vegetation coverage and activity can accelerate the montane hydrological regimes. However, the climate impacts on ecohydrology of forested valleys of the Himalaya are uncertain. In this study, utilizing results of about three centuries of cellulose isotope chronologies (δ 13C and δ 18O) of dominant tree species, geo-chronological proxies, bio-geophysical dataset and simulations including satellite observations, we show an activation in the ecophysiological processes including evapotranspiration (ET) since the 1950s. Observation suggests rapid greening, while isotopic records indicate enhanced assimilation and transpiration in deciduous species vis-à-vis conifers post 1950s. Given strong vegetation-precipitation feedback and superimposed on the increasing trends of conducive atmospheric factors affecting valley-scale convective processes, intensification in forest ET is manifesting in a progressive enhancement in extreme rainfall events (EREs) since the last few decades. Results suggest that representation of ecophysiological processes and dynamics of seasonal moisture loading in observational and modelling framework is critical for understanding EREs under climate change.

The Himalaya, the geodynamically active youngest mountain system of the Earth, due to high environmental variability supports rich biodiversity, which makes the fundamental basis for ecosystem services that constitute the basic life support for human being. Most of the life support commodities, such as food, shelter, water, quality air and medicine directly or indirectly depend on plant diversity. However, due to climate change and growing anthropogenic pressure ecosystem structure and function is greatly affected posing threat to the availability of biotic resources on sustained basis. Ground and space based observations show that the biozones across the Himalaya have experienced changes in vegetation in recent decades. Many of the high-elevation temperature sensitive plant species are known to be shifting to higher elevations in the Himalayan region, though the rate of shift being highly species and site idiosyncratic. Increasing magnitude of ecosystem fragmentation associated with the developmental activities coupled with projected warming in the twenty-first century could pose a serious threat to biodiversity that include many of the endemic plant species, progenitors of cultivated and economic plants. The change in climatic conditions also accelerates the invasion of alien species having competitive edge over the indigenous ones. Commendable steps have been recently taken for in-situ conservation of species through the establishment of protected areas across the elevations in the Himalayan region. However, species specific ecological studies and long-term ecological monitoring essentially required to understand relative sensitivity of species to environmental changes in the Himalayan region are still lacking. Such empirical studies in long-term perspective are required to adopt appropriate biodiversity management plans for the Himalayan region. For this it is required to ascertain chronology of species dynamics in relation to environmental changes using precisely dated growth rings of plant species. This should provide appropriate clue to the absolute chronology of species dynamics in response to environmental changes.

Tree-ring δ18O values are a sensitive proxy for regional physical climate, while their δ13C values are a strong predictor of local ecohydrology. Utilizing available ice-core and tree-ring δ18O records from the central Himalaya (CH), we found an increase in east–west climate heterogeneity since the 1960s. Further, δ13C records from transitional western glaciated valleys provide a robust basis for reconstructing about 3 centuries of glacier mass balance (GMB) dynamics. We reconstructed annually resolved GMB since 1743 CE based on regionally dominant tree species of diverse plant functional types. Three major phases became apparent: positive GMB up to the mid-19th century, the middle phase (1870–1960) of slightly negative but stable GMB, and an exponential ice mass loss since the 1960s. Reasons for accelerated mass loss are largely attributed to anthropogenic climate change, including concurrent alterations in atmospheric circulations (weakening of the westerlies and the Arabian Sea branch of the Indian summer monsoon). Multi-decadal isotopic and climate coherency analyses specify an eastward declining influence of the westerlies in the monsoon-dominated CH region. Besides, our study provides a long-term context for recent GMB variability, which is essential for its reliable projection and attribution.

General comments: This paper of Singh et al. reconstructed and analyzed the glacier mass balance since 1743 in central Himalaya, using tree ring carbon isotope, it is meaningful for the understanding the glacier variation in Himalaya area. Response: We are thankful to the reviewer for valuable comments and suggestions that improved this manuscript. In this paper, we reconstructed annual variability of four ‘benchmark glaciers’ of the Uttarakhand Himalaya utilizing tree-ring carbon isotopes of two dominant conifer species growing in the valleys. We also analyzed the variability of tree-ring and ice-core oxygen isotopes on a central Himalayan-scale. Comment: However, the

Our understanding on glacier-climate link in the Himalayan region is constrained due to lack of long-term observational and high-resolution proxy records. Hostile weather conditions and difficult approaches to access glaciers due to rough terrains largely limit observational studies on glaciers in the Himalaya. Sub-alpine trees and shrubs close to glaciers, growth of which is very sensitive to fluctuations in temperature, provide precise continuous record on climate and glacier behaviour to supplement the observational records back to several centuries. To unfold the Gangotri glacier dynamics in the past, we developed tree-ring chronologies and studied the colonization pattern of the trees in the region. Tree-ring chronologies of Himalayan birch and Himalayan pine developed from their respective upper tree line ecotone in the Gangotri glacier forefields showed impact of temperature on the growth variations. A comparison of Himalayan pine chronology with temperature proxies revealed regional and hemispheric scale temperature signal. Using tree-ring chronologies we show expansion (retreat) of the Gangotri glacier during cool (warm) phases that are also in agreement with the glacier fluctuation records from Central Asia and Southern Tibet. Moreover, using tree colonization pattern in the glacier forefields we established for the first time that the Gangotri glacier terminus receded similar to 1.853 km since the late 16th century (1571 C.E.), major part of which (1.79 km) receded since 1935 C.E. The glacier retreat, associated with the onset of 20th century warming got accelerated since 1957 C.E. (1.567 km). In view of our findings, the Gangotri glacier might further face accelerated recession in the 21st century under the projected warming.

Tree-rings have been extensively used to develop temperature reconstructions using conifer species growing in different parts of the Himalaya. The reconstructions are based on the existence of both positive and negative relationship between the tree-ring chronologies and instrumental temperature records. However, the reconstructions based on positive relationship between tree-ring and temperature series are few. Regional temperature reconstructions developed using tree-ring series have revealed a significant correlation with the regional data which degraded gradually with distance from the tree-ring sampling sites indicating dominant orographic control on climate. On critical assessment of the available tree-ring-based temperature reconstructions, glaring anomalies were reported especially in case of the extreme years coinciding with the volcanic eruption associated cooling. Tree-ring-based reconstructions from Kashmir and Nepal, where temperature has direct forcing on tree-ring widths, indicated unusually cold temperatures in 1816, coinciding with the Tambora volcanic eruption in April 1815 in Indonesia. However, in the case of the chronologies having negative relationship with temperature, usually warmer conditions are reconstructed against the narrow rings usually observed in 1816. The narrow rings in 1816 could have been caused due to volcanic eruption induced cooling as well as reduced solar radiation restricting the photosynthesis. Thus changes in the limiting factor led to the break in relationship between tree-ring indices and climate parameters. In view of this, it is suggested that the environmental variables having direct relationship with tree growth should be reconstructed from tree-ring chronologies as there exists a fair possibility that the growth limiting factor such as temperature remains stable over time.

Tree-rings have been extensively used to develop temperature reconstructions using conifer species growing in different parts of the Himalaya. The reconstructions are based on the existence of both positive and negative relationship between the tree-ring chronologies and instrumental temperature records. However, the reconstructions based on positive relationship between tree-ring and temperature series are few. Regional temperature reconstructions developed using tree-ring series have revealed a significant correlation with the regional data which degraded gradually with distance from the tree-ring sampling sites indicating dominant orographic control on climate. On critical assessment of the available tree-ring-based temperature reconstructions, glaring anomalies were reported especially in case of the extreme years coinciding with the volcanic eruption associated cooling. Tree-ring-based reconstructions from Kashmir and Nepal, where temperature has direct forcing on tree-ring widths, indicated unusually cold temperatures in 1816, coinciding with the Tambora volcanic eruption in April 1815 in Indonesia. However, in the case of the chronologies having negative relationship with temperature, usually warmer conditions are reconstructed against the narrow rings usually observed in 1816. The narrow rings in 1816 could have been caused due to volcanic eruption induced cooling as well as reduced solar radiation restricting the photosynthesis. Thus changes in the limiting factor led to the break in relationship between tree-ring indices and climate parameters. In view of this, it is suggested that the environmental variables having direct relationship with tree growth should be reconstructed from tree-ring chronologies as there exists a fair possibility that the growth limiting factor such as temperature remains stable over time.

Comments to authors: The manuscript, titled "Central Himalayan tree-ring isotopes reveal increasing regional heterogeneity and enhancement in ice-mass loss since the 1960s", tries to address the correlation between δ 13C and glacier mass balance and their temporal evolution in the past. The authors provided a detailed description of their tree ring isotope measurements and showed a decent correlation with the reconstructed glacial mass balance for the past 273 years in the central Himalaya. The authors attempted several different statistical tests and presented their results. The results clearly show a shift in climate proxies since 1960’s. The supplementary figures

There are knowledge gaps in the long-term changes in Indian summer monsoon rainfall (ISMR, June–September) behaviour, which affects the livelihood of large population in the Indian subcontinent. To better understand ISMR variability, we reconstructed June–July rainfall for the period 1743–2015 CE from Dingad valley, Uttarakhand, central Himalaya using δ18O variations in tree rings. For this, regional mean tree-ring isotope chronology, prepared by merging δ18O chronologies of two conifer (Abies pindrow (Royle ex D.Don) Royle and Picea smithiana (Wall.) Boiss) and one broadleaf deciduous species (Aesculus indica (Wall. ex Camb.) Hook), was used. The reconstructed rainfall series revealed significant correlations with the observational monsoon records from different regions of India. The most conspicuous feature in our reconstructed series is a decreasing rainfall trend since 1743 CE with the driest period in the late 20th and early 21st centuries, which is consistent with other monsoon rainfall proxies from a large part of the south Asian monsoon region (India, Nepal, Bhutan, Myanmar and Tibet Plateau). Consistency of reconstructed series with instrumental records and proxies from different regions revealed the capture of regional scale rainfall features in our data testifying its utility in understanding ISMR variability in long-term perspective.

The instrumental weather records from the western Himalayan region for the past century show an increase in annual mean atmospheric temperature with winters warming at a faster rate. The vegetation of the upper ecotonal zones, already on the climatic threshold is sensitive to any such change in climate variable most limiting the growth. To investigate the impact of climate change on treeline dynamics of Himalayan pine (Pinus wallichiana A. B. Jackson), we investigated its recruitment pattern in 12 treeline sites of different ecological settings widely distributed in monsoon and monsoon-shadow zones in the western Himalaya, India. The study explicitly revealed that Himalayan pine treeline has shifted towards the upper elevation in the investigated sites, but with varying rate (11-54 m/10 yrs) largely due to site-specific microclimatic and biotic factors. Tree-ring-width chronologies of Himalayan pine prepared from two upper forest border sites, one each in monsoon and monsoon-shadow zone, respectively revealed that winter and early spring season mean temperature has direct relationship with the radial growth of trees. This indicates that the photosynthetic assimilates during winter and early spring seasons significantly influence the ensuing year's tree growth. The sensitivity of Himalayan pine to climate change revealed in this study indicates that the projected climate change under the background influence of greenhouse gases could have serious implications on biodiversity of upper elevations in the western Himalaya. (C) 2016 Elsevier Ltd and INQUA. All rights reserved.

The entire Indo-Himalayan region from northwest (Kashmir) to northeast (Assam) is facing prevalence of floods and landslides in recent years causing massive loss of property, human and animal lives, infrastructure, and eventually threatening tourist activities substantially. Extremely intense rainfall event of 2013C.E. (between 15 and 17 June) kicked off mammoth flash floods in the Kedarnath area of Uttarakhand state, resulting in huge socioeconomic losses to the state and country. Uttarakhand is an important hilly region attracting thousands of tourists every year owing to numerous shrines and forested mountainous tourist spots. Though recent studies indicate a plausible weakening of Indian summer monsoon rainfall overall, recurrent anomalous high rainfall events over northwest Himalaya (e.g. -2010, 2013, and 2016) point out the need for a thorough reassessment of long-term time series data of regional rainfall and ambient temperatures in order to trace signatures of a shifting pattern in regional meteorology, if any. Accordingly, here we investigate ~100-year-long monthly rainfall and air temperature time series data for a selected grid (28.5°N, 31.25°N; 78.75°E, 81.25°E) covering most parts of Uttarakhand state. We also examined temporal variance in interrelationships among regional meteorological data (temperature and precipitation) and key global climate variability indices using advance statistical methods. Major findings are (i) significant increase in pre-monsoon air temperature over Uttarakhand after 1997, (ii) increasing upward trend in June–July rainfall and its relationship with regional May temperatures (iii) monsoonal rainfall (June, July, August, and September; JJAS) showing covariance with interannual variability in Eurasian snow cover (ESC) extent during the month of March, and (iv) enhancing tendency of anomalous high rainfall events during negative phases of Arctic Oscillation. Obtained results indicate that under warming scenario, JJ rainfall (over AS) may further increase with occasional extreme rainfall spells when AO index (March) is negative.

Precipitation in the monsoon shadow zone of the western Himalayan region, largely under the influence of mid-latitude westerlies, is the dominant regional socioeconomic driver. Current knowledge of long-term regional precipitation variability is scarce due to spatially and temporally limited weather and high-resolution proxy climate records. We developed the first boreal spring precipitation reconstruction for the western Himalaya covering the last millennium (1030–2011 C.E.). The annually resolved reconstruction is based on a large tree-ring data set of Himalayan cedar (Cedrus deodara) and neoza pine (Pinus gerardiana) from 16 ecologically homogeneous moisture stressed settings in Kinnaur, western Indian Himalaya. The precipitation reconstruction revealed persistent long-term spring droughts from the 12th to early 16th century C.E. and pluvial from the late 16th century C.E. to recent decades. The late 15th and early 16th centuries (1490–1514 C.E.) displayed the driest episode, with precipitation being ∼15% lower than the long-term mean. The early 19th century (1820–1844 C.E.) was the wettest period of the past millennium, with mean precipitation ∼13% above the long-term mean. The reconstructed boreal spring precipitation from the western Himalaya revealed large-scale consistency with hydrological records from westerly dominated regions in Central Asia, indicating synoptic-scale changes in atmospheric circulation during the major part of the Medieval and Little Ice Age periods. Protracted droughts in Central Asia could have caused severe contraction of the regional economy, as indicated by striking coherence of reconstructed drought periods and historic social upheavals and invasions of India from Central and Western Asian invaders. Vulnerability to climatic extremes underpins the need to develop a better understanding of the temporal and spatial variability in regional hydroclimate in order to devise viable water resource management plans.

Droughts in semi-arid and arid regions of the northwest Himalaya are very common causing distress to socioeconomic systems. Our understanding on natural variability in droughts in the northwest Himalaya in long-term perspective is limited largely due to paucity of observational and high-resolution proxy records. We developed a 275-years (A.D. 1740–2014) long Standardized Precipitation Index (eight months SPI of May, SPI8-May) reconstruction using ring-width chronology of Himalayan cedar (Cedrus deodara (Roxb.) G. Don) from Kishtwar, Jammu and Kashmir in the northwest Himalaya, India. The most conspicuous feature of reconstruction is pluvial 1950s, 1990s and dry 1970s. The wettest phase of 1990s is followed by a distinct drying since 2000s in Kishtwar. The reconstructed SPI8-May series showed very good consistency with tree–ring-based upper Indus basin discharge and gridded summer (June–July–August) PDSI data of the northwest Himalaya–Karakoram region. Such a consistency in SPI8-May, Indus discharge and summer PDSI in westerly dominated region of the Himalaya–Karakoram region underscores potential utility of SPI reconstructions in understanding climate change over the region in long-term perspective.

The impact of climate change in high-elevation areas is acknowledged to have wide ranging implications on environment relevant to human society. However, our understanding of climate change in the high-elevation eastern Himalayan region is hampered due to temporally and spatially limited weather records. Using ring-width chronology of larch (Larix griffithiana) from high-elevation North Sikkim, we developed mean late summer (July-August-September (JAS)) temperature reconstruction extending back to AD 1852. The reconstructed mean JAS temperature shows warming since the 1930s, with 1996-2005 being the warmest in context of the past similar to 150 years. We found that the warming trend reported here is consistent with other climate change indicators such as plant species migration to higher ranges and accelerated glacier retreats in Sikkim. Temporal and spatial extent of such annually resolved records need to be expanded for the data scarce eastern Himalayan region to understand regional variability and feedbacks in climate. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.

The Meghalaya state is facing serious environmental degradation due to rapidly increasing cement industry in the last few decades. The cement factories are directly draining their untreated effluents into the fresh water streams. The exotic caves present in these areas are under major threat with extensive mining of limestone and mixing of untreated factory effluent in the cave water. Major ion chemistry of water samples collected from Krem Mawkhyrdop, Wah Mawkhyrdop stream and Krem Umsynrange revealed that the Krem Mawkhyrdop water contains Ca2+ and SO42- ions more than permissible limit in drinking water. Carbonate weathering is the major source of Ca2+ and HCO3- ions in the area. Anthropogenic activities are responsible for high concentration of calcium and sulphate in the cave water. The untreated effluent discharge from cement factories located upstream of caves, added by limestone and coal mining influence the major ion chemistry of the cave water and polluting the surface, cave and ground water system.

February–June (FJ) mean temperature records (AD 1455–2002) were developed using ring-width chronologies of Cedrus deodara from three sites in Tons valley, western Himalaya, India. The reconstructed series captured 30-year coolest (AD 1911–1940) and warmest (AD 1941–1970) periods in the 20th century in the last 548 years. The 20th century warming trend is not evident in our reconstructed temperature data, which is also consistent with the instrumental records. The reconstruction showed strong association with corresponding season's rainfall in the northern mountainous region, north-west India and February–May rainfall in north central India. The reconstructed temperature data also revealed inverse relationship with precipitation record developed from adjacent sites in Kumaon region, western Himalaya. Such a strong association with precipitation underscores the utility of data in understanding climate change behavior over this region of the western Himalaya, India.

We have developed the first annually resolved ringwidth chronology (AD 1880-2002) of chir pine (Pinus roxburghh) from Balcha in Tons valley, western Himalaya. The existence of significant positive relationship between ring-width indices and June August mean temperature obtained in cross-correlation analysis endorsed the dendroclimatic potential of chir pine chronologies. Using such strong relationship, statistically verifiable first chir pine chronology-based June August temperature (AD 1880-2001) was reconstructed for the western Himalaya. The calibration model capturing 16% of the variance in instrumental data (AD 1901-1998) showed that the network of such chronologies should help in developing robust temperature records for the western Himalaya.