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As direct observations of rockfalls are rare and difficult to obtain over long timescales, stem injuries and their dating with dendrogeomorphic techniques have been applied frequently in the past to reconstruct process activity. However, the analysis of tree-ring samples requires considerable temporal efforts, which can be detrimental in applied research and expert opinions. To compensate for this shortcoming, several studies have lately explored the potential of the counting of visible scars as an alternative method to dendrogeomorphology as it requires much less time and human efforts to reconstruct spatial patterns of rockfall activity. Yet, to date, both approaches have not been compared at the same site. In this paper, based on the extensive analysis of 278 conifer and broadleaved trees (from which 1097 tree-ring cores were extracted) from a mixed forest plot of the Vercors Massif (French Alps), we demonstrate that both methods provide similar spatial patterns of rockfall activity with a strong increase of recurrence intervals down the talus slope and a clear lateral zonation of activity. Despite this apparent convergence between both approaches, our study also evidences that rockfall frequencies strongly differ with tree species and diameter: the visual inspection of conifer stems and the analysis of tree-ring signals in large-diameter broadleaved trees typically lead to an overestimation of recurrence intervals. Based on these findings, we recommend giving priority to the scar-counting approach on small diameter (<15 cm) broadleaved stems and to restrict tree-ring analysis to old conifers that are more susceptible – through the identification of tangential rows of traumatic resin ducts – to provide reliable estimations of long recurrence intervals (as generally observed in the lower portions of the slope). These guidelines should help to improve the reliability of recurrence interval maps of rockfall process activity in forests further, but also to improve cost-benefit ratios of future studies. • Comparison of the counting scar and dendrogeomorphic approaches to reconstruct rockfall in a mixed forest stand • Both approaches provide comparable spatial patterns with an increase of recurrence intervals down the talus slope • Rockfall frequency differs quite substantially with tree species and diameter. • Tree-ring signals in large-diameter broadleaved trees typically lead to an overestimation of recurrence intervals • Our study provides key guidelines to improve the reliability of rockfall hazard zoning [ABSTRACT FROM AUTHOR]

Abstract Due to intense urban sprawl in rockfall-prone areas, a precise rockfall risk assessment has become a crucial issue for public authorities and stakeholders. In this context, quantitative risk analysis (QRA) procedures, accounting for the specificities of the rockfall process, have been developed. For the last few decades, several studies have examined the impacts of global warming on rockfall activity, especially at high-altitude sites. However, the influence of land-use and land-cover (LULC) changes, very frequent at lower altitudes and in the vicinity of urbanised areas, on rockfall propagation and associated risks has received little attention. This study proposes a holistic QRA on a municipality scale (the municipality of Crolles, in the French Alps) that includes both all the potential release areas at the whole cliff scale and a wide spectrum of rockfall volumes randomly extracted from volume classes distributed between 1 and 20 m3. In addition, to quantify precisely the effect of LULC changes on rockfall risk, four characteristic scenarios representative of LULC changes observed in the municipality and more generally in the Alps since the mid-19th century, have been included in the analysis. The results demonstrate the significant impacts of landscape reorganisation on the spatial distribution of risk with increasing forest cover, which can be counterbalanced by evolving LULC in a transition unit located between the forest strip and the urban front. They also evidence that a large proportion of the risk is explained by small block volumes, which are the most affected by landscape structure and evolution. From a practical point of view, and despite several uncertainties related to different modelling assumptions, the results reported herein clearly demonstrate the applicability and the value of QRA for rockfall risk management at a municipality scale in a context of rapid and intense environmental changes. Highlights • Holistic rockfall QRA accounting for non-stationary conditions • Important contribution of small volumes affected by landscape structure on total risk • Significant impacts of landscape reorganization on the spatial risk distribution [ABSTRACT FROM AUTHOR]

Due to the scarcity of reliable and highly resolved moisture proxies covering much of the Holocene, there has been increased interest in the study of living and subfossil peatland trees sensitive to gradual and extreme changes in hydrology, precipitation, and related environmental processes. Peatland development and the associated carbon accumulation, which are strongly influenced by hydrological fluctuations, are also of prime importance as peatlands represent long-term sinks of atmospheric carbon. Improved knowledge of peatland development and soil moisture variability during the Holocene is therefore essential to our understanding of long-term hydroclimate changes, the terrestrial carbon cycle, and to enable more robust predictions of peatland response to future climate changes. Here, we review the existing mid- to late Holocene peatland tree-ring chronologies that have been used to study climate variability on (sub-)annual to centennial scales with a primary focus on northern Europe. Since the 1970s, absolutely dated tree-ring chronologies covering substantial parts of the Holocene have been developed from excavated remains of oak ( Quercus spp.) and pine ( Pinus sylvestris L.). The annual tree-ring patterns of these trees are often characterized by periods of depressed growth reflecting annual to decadal hydroclimatic changes. In addition, changes in the spatio-temporal distribution of trees throughout the Holocene are often found to reflect decadal to centennial climate and hydrological changes. Moreover, synchronicity between tree-ring chronologies and tree-population dynamics over larger geographical areas show periods of coherent regional climate forcing, especially during the mid-Holocene. This review (i) provides an overview of pioneering and recent studies presenting tree-ring chronologies developed from subfossil peatland trees, and (ii) presents recent developments in the fields of dendroecology (i.e. the response of tree growth and changes in vitality as a result of changes in climatic variables) and dendroclimatology (i.e. the reconstruction of climate fluctuations based on tree-ring analyses) in peatland regions. Moreover, we (iii) use long-term climate reconstructions based on alternative proxies for comparison, and (iv) present different ways to analyse tree-ring records to generate novel information on annual to centennial timescales. This analysis is based on an unprecedented network of tree-ring chronologies from Denmark, Finland, Germany, Great Britain, Ireland, Lithuania, the Netherlands, Poland, Sweden, and Canada, as well as a wealth of old and previously (un) published literature from Scandinavia and Germany, which has not been accessible to a wider audience in the past due to inaccessibility or linguistic barriers. Finally, a map of possible hotspots for the assessment of continuous peatland-tree studies is presented, along with suggestions for new research directions in the field. [ABSTRACT FROM AUTHOR]

Long-term records of rockfalls have proven to be scarce and typically incomplete, especially in increasingly urbanized areas where inventories are largely absent and the risk associated with rockfall events rises proportionally with urbanization. On forested slopes, tree-ring analyses may help to fill this gap, as they have been demonstrated to provide annually-resolved data on past rockfall activity over long periods. Yet, the reconstruction of rockfall chronologies has been hampered in the past by the paucity of studies that include broadleaved tree species, which are, in fact, quite common in various rockfall-prone environments. In this study, we test the sensitivity of two common, yet unstudied, broadleaved species — Quercus pubescens Willd. ( Qp ) and Acer opalus Mill. ( Ao ) — to record rockfall impacts. The approach is based on a systematic mapping of trees and the counting of visible scars on the stem surface of both species. Data are presented from a site in the Vercors massif (French Alps) where rocks are frequently detached from Valanginian limestone and marl cliffs. We compare recurrence interval maps obtained from both species and from two different sets of tree structures (i.e., single trees vs. coppice stands) based on Cohen's k coefficient and the mean absolute error. A total of 1230 scars were observed on the stem surface of 847 A. opalus and Q. pubescens trees. Both methods yield comparable results on the spatial distribution of relative rockfall activity with similar downslope decreasing recurrence intervals. Yet recurrence intervals vary significantly according to tree species and tree structure. The recurrence interval observed on the stem surface of Q. pubescens exceeds that of A. opalus by > 20 years in the lower part of the studied plot. Similarly, the recurrence interval map derived from A. opalus coppice stands, dominant at the stand scale, does not exhibit a clear spatial pattern. Differences between species may be explained by the bark thickness of Q. pubescens , which has been demonstrated to grow at twice the rate of A. opalus , thus constituting a mechanical barrier that is able to buffer low energy rockfalls and thus can avoid damage to the underlying tissues. The reasons for differences between tree structures are related to the clustered coppice-specific spatial stem distribution in clumps that could result on one hand in bigger gaps between clumps, which in turn decreases the probability of tree impacts for traveling blocks. On the other hand, data also indicate that several scars on the bark of coppice stands may stem from the same impact and thus may lead to an overestimation of rockfall activity. [ABSTRACT FROM AUTHOR]

Aims: To compare growth variability of Scots pine ( Pinus sylvestris L.) on different soil types, and to assess the potential of peat-soil pines for climatological and hydrological studies. Methods: We used extensive dendrochronological analyses to investigate temporal and spatial responses of pines growing on peat soils and mineral soils in three regions of Lithuania. Results: Significant correlations were observed between tree populations growing on similar soil types in different geographical regions, whereas synchronicity was absent between neighbouring stands growing on different soil types. At mineral soils, tree growth was significantly correlated with winter and early summer temperatures, whereas a more complex response was detected in peat-soil trees, presumably reflecting a multi-annual synthesis of moisture variability and changing hydrology. Synchronous long-term peat soil tree-growth variations observed over large parts of the Baltics point to a possible regional hydrological forcing. Our results may therefore improve hydrological reconstructions using living and subfossil peat-soil trees, and could be of prime importance given the major influence peatland water-table fluctuations have on a range of environmental processes. Conclusion: Results reveal that peat-soil pines are unsuitable for high-frequency climate reconstruction, but demonstrate their potential for the reconstruction of multi-annual to decadal hydrological fluctuations. Mineral-soil pines, by contrast, should be used for temperature reconstructions. [ABSTRACT FROM AUTHOR]

Abstract: Trees affected by mass movements record the evidence of geomorphic disturbance in the growth-ring series, and thereby provide a precise geochronological tool for the reconstruction of past activity of mass movement. The identification of past activity of processes was typically based on the presence of growth anomalies in affected trees and focused on the presence of scars, tilted or buried trunks, as well as on apex decapitation. For the analyses and interpretation of disturbances in tree-ring records, in contrast, clear guidelines have not been established, with largely differing or no thresholds used to distinguish signal from noise. At the same time, processes with a large spatial footprint (e.g., snow avalanches, landslides, or floods) will likely leave growth anomalies in a large number of trees, whereas a falling rock would only cause scars in one or a few trees along its trajectory. Based on the above considerations, we examine issues relating to the interpretation and dendrogeomorphic dating of mass movements. Particular attention is drawn to sampling in terms of sample distribution across a study site, the actual selection of trees as well as to sample size (i.e., number of trees sampled). Based on case studies from snow avalanche, debris flow, and landslide sites, we demonstrate that thresholds can indeed improve dating quality and, at the same time, minimize noise in time series. We also conclude that different thresholds need to be used for different processes and different periods of the reconstruction, especially for the early stages of the reconstruction when the number of potentially responding trees will be much smaller. This paper seeks to set standards for dendrogeomorphic fieldwork, analysis, and interpretation for different processes of mass movements. [Copyright &y& Elsevier]

• We present a 700-year flood history for an Alpine catchment using documentary and systematic data. • The comprehensive flood dataset aligns well with the long-term flood variability from the Swiss Alps. • We model discharge for 32 historical floods using archival records, topographic maps, and engineering plans. • Past mitigation works effectively helped to protect the city of Brig-Glis from major flood damage. • The inclusion of historical data improves flood discharge estimates for longer return periods. Flood marks and descriptions of past floods in archival records are valuable sources of information to complement the often short – and sometimes lacunary – systematic records provided by gauge stations, especially in mountain and smaller catchments for which the network of recording stations is still fragmentary. Yet, historical accounts of floods are only rarely used to calculate discharge during past floods and to complement estimates of flood frequency and magnitude. This is because the definition of flood types and the reconstruction of past topography of the now urbanized riverscapes is often challenging. Here, we employ an approach by which we combine (i) archival (1331–1965) and continuous gauge (1966–2020) records of past floods, (ii) information on past topography and mitigation measures found on topographic maps and contemporary documents specifying the dimensions of contemporary engineering plans and (iii) a hydraulic model to derive a c. 700-year history of flood activity and related discharges for the Saltina River, Brig-Glis (Valais, Swiss Alps). Periods of increased flood activity match with flood-rich episodes in the Rhone River and high lake levels at Lago Maggiore (Ticino), and the time series passes stationarity tests since at least 1828 CE. For a total of 32 floods occurring prior to the installation of the gauge station in 1966, we provide discharges following a descriptive classification, and demonstrate that major floods occurred in 1755 (∼140 m3s−1), 1828 (∼160 m3s−1), and 1921 (∼120 m3s−1). We also evidence that the construction of mitigation measures has contributed to a reduction in flood frequency, but that the occurrence of extraordinary floods has again been on the rise since the early 21st century. [ABSTRACT FROM AUTHOR]

Abstract The impact climate and land-use changes have on the hydrological conditions in peat bogs and lakes is often complex, but of great importance for the carbon budget and biodiversity in these ecosystems. Links and feedbacks between raised bog water table depth, lake level, net precipitation, hydrometeorological indices, and radial tree growth have been studied and identified in the Rėkyva wetland complex, Lithuania. Moreover, several statistically significant correlations between raised bog water table depths, lake level, local river runoff, and tree growth were observed. The changes of raised bog water table, lake level, and tree growth show synchronous trends despite variations in the absolute values. Our results show decreasing water table in the Rėkyva wetland complex over the last 100 years, especially in the middle of the 20th century. This study also shows a potential for reconstructing water table fluctuations in wetland complexes using multi-indicator approaches. Our observations and reconstruction show consistency with several regional studies and reconstructions of moisture variations in Baltic raised bogs, at least for periods without strong anthropogenic influences. Highlights • Hydrological conditions in wetlands are reconstructed with a multi-proxy approach. • Runoff data from local rivers are a suitable indicator of water storage in wetlands. • Ring widths of wetland pines depend on hydrological site conditions. • Driest conditions in the studied wetland were in the middle of the 20th century. [ABSTRACT FROM AUTHOR]

Abstract Due to the scarcity of reliable palaeoecological and climatic proxy records from the Eastern Baltic covering the Holocene, there has been increased interest for multi-proxy studies in the region to detect local to regional environmental changes. The Čepkeliai wetland complex, SE Lithuania, provides an uninterrupted Holocene sediment sequence, which is used here to reconstruct palaeoenvironmental history in the southern part of the Eastern Baltic. High-resolution lithological (LOI, magnetic susceptibility), palaeobotanical (pollen, plant macrofossil, tree rings), isotopic (14C) and geochemical data were employed to reconstruct the peculiarities of vegetation and hydroclimate dynamics, as well as to discuss results in a local to regional context. Temporal lags of environmental reactions to Holocene climatic warming were recorded both in lithostratigraphical and biostratigraphical data, thus confirming regional significance of this phenomenon. A deep meso- to eutrophic basin – influenced by high surface runoff and surrounded by early boreal forest – existed at the site until about 11,300 cal BP. Thereafter, immigration of thermophylous taxa such as Ulmus (since 10,700–10,800 cal BP), Corylus (since 10,400–10,300 cal BP), Tilia and Quercus (after 9500 cal BP) as well as changes in the limnic environment point to an amelioration of the environmental situation, i.e. to a predominance of a warm and dry climatic regime. Instability of palaeobotanical and lithological records suggests that environmental anomalies of the Early Holocene occurred at about 11,200–11,000 cal BP, 10,600–10,300 cal BP, and 8200-7800 cal BP. These anomalies are thus contemporaneous with the pronounced climatic shifts (i.e. dry and cool intervals) known at the continental scale. An expansion of Picea was facilitated by the 8200-7800 cal BP climatic shift whereas early establishment of Alnus glutinosa suggests an onset of a wet interval (10,200 cal BP) which was previously unknown in the area. The stepwise lowering of the water table noted at about 7300–7200 and 6600–6700 cal BP, with the termination of the lake-phase and change to telmatic environment after 6100 cal BP, proves the positive reaction of the site to the dry climatic reversals of the Middle Holocene. Following the decay of the broad-leaved thermophilous forest after 4500 cal BP, a cold climatic reversal favored the formation of a diverse mosaic-like vegetation which was then replaced by homogenous Pinus-Picea vegetation after 3400 cal BP. The climatic and site-specific factors have been playing a leading role in the development of the site whereas signals of human interference remain negligible. [ABSTRACT FROM AUTHOR]

Expected runout distances and related return periods are the most important parameters needed for zoning in terrain prone to snow avalanching. Hazard mapping procedures usually allocate areas of land to zones with a different degree of danger based on return periods estimated for given snow volumes in the starting zone or with statistical/dynamical models. On forested avalanche paths, dendrogeomorphology has a great potential to add critical input data to these calculations in terms of recurrence intervals or return periods. However, quite paradoxically, recurrence interval maps of snow avalanches have only rarely been retrieved from tree-ring analysis and mostly represent the inverse of the mean frequency of avalanches that could be retrieved locally rather than the return period. The purpose of this study therefore was to propose a consistent approach for tree-ring based recurrence interval mapping of snow avalanche events. On the basis of 71 snow avalanches retrieved from 2570 GD growth disturbances identified in 307 larch trees from three avalanche paths located in the vicinity of Täsch (Canton of Valais, Swiss Alps), we first followed the classical approach used in dendrogeomorphology and derived recurrence interval maps through interpolation from recurrence intervals observed at the level of individual trees. We then applied an expert delineation of the spatial extent of past events based on the location of disturbed trees. Our results show that the second step improved representation of expected patterns of recurrence intervals that typically increase as one moves down the centerline of the avalanche path. Despite remaining limitations and uncertainties precluding from direct use of our maps for hazard mapping purpose, these results suggest that dendrogeomorphic time series of snow avalanches can yield valuable information for the assessment of recurrence intervals of avalanches on forested paths for which only very limited or no historical data exists, and that this data can be obtained independently from meteorological data or numerical modeling. [ABSTRACT FROM AUTHOR]

Continuous water-table (WT) measurements from peatlands are scarce and – if existing at all –very short. Consequently, proxy indicators are critically needed to simulate hydrological changes in peatlands over longer time periods. In this study, we demonstrate that tree-ring width (TRW) records of Scots pine ( Pinus sylvestris L.) growing in the Čepkeliai peatland (southern Lithuania) can be used as a proxy to reconstruct hydrological variability in a raised bog environment. A two-step modelling procedure was applied to extend existing measurements and to develop a new and longer peatland WT time series. To this end, we used instrumental WT measurements extending back to 2002, meteorological records, a P-PET (difference between precipitation and potential evapotranspiration) series covering the period 1935–2014, so as to construct a tree-ring based time series of WT fluctuations at the site for the period 1870–2014. Strongest correlations were obtained between average annual WT measured at the bog margin and total P-PET over 7 years (r = 0.923, p < 0.00001), as well as between modelled WT and standardized TRW data with a two years lag (r = −0.602, p < 0.001) for those periods where WT fluctuated at the level of pine roots which is typically at <50 cm depth below the peat surface. Our results suggest that moisture is a limiting factor for tree growth at peatlands, but below a certain WT level (<50 cm under the soil surface), drought becomes a limiting factor instead. To validate the WT reconstruction from the Čepkeliai bog, results were compared to Nemunas river runoff since CE 1812 (r = 0.39, p < 0.00001, 1870–2014). We conclude that peatlands can act both as sinks and sources of greenhouse gases in case that hydrological conditions change, but that hydrological lags and complex feedbacks still hamper our understanding of several processes affecting the hydrology and carbon budget in peatlands. We therefore call for the development of further proxy records of water-table variability in peatlands to improve our understanding of peatland responses to climatic changes. [ABSTRACT FROM AUTHOR]

Twenty-five tree-ring width (TRW) chronologies, developed from moisture sensitive peatland trees in Sweden and Lithuania, and representing eight periods during the mid-Holocene to present, were analysed regarding common periodicities (cycles). Periods of 13–15, 20–22, and 30–35 years were found in most chronologies, while 8–10, 18–19, and 60–65 year periodicities were observed as well, but less commonly. Similar periodicities, especially about 15 and 30 years in duration, were detected in both living and subfossil trees, indicating that the trees have responded to similar forcing mechanisms on those timescales through time. Some of the detected periods may be related to solar variability and lunar nodal tides, but most of the detected periodicities are more likely linked to hydrological changes in the peatlands associated to atmospheric patterns such as the North Atlantic Oscillation (NAO), or variations in sea surface temperatures (i.e. the Atlantic Multidecadal Oscillation, AMO). However, no significant relationships between tree growth, NAO and AMO could be formally established, possibly due to hydrological lag and feedback effects which are typical for peatlands but render in-depth assessments rather difficult. [ABSTRACT FROM AUTHOR]

Debris-flow activity in the Alps is anticipated to undergo pronounced changes in response to a warming climate. Yet, a fundamental challenge in comprehensively assessing changes in process activity is the systematic lack of long-term observational debris-flow records. Here, we reconstruct the longest, continuous time series (1626-2020) of debris flows at Multetta, a supply-limited torrential system in the Eastern Swiss Alps. Relying on growth-ring records of trees that were damaged by debris flows, we do not detect significant changes in the frequency or magnitude over time. This seeming absence of a direct climatic influence on debris-flow initiation aligns with the regular distribution of repose time patterns, indicating a dependence of local process activity on sediment discharge and recharge. This stark difference in process behavior between our supply-limited site and transport-limited catchments has implications for assessing torrential hazard and risk mitigation in a context of global warming., (© 2024. The Author(s).)

X-ray computed tomography (XRCT) imaging allows non-destructive visualization of the structure of various materials. Applied to wooden objects, it allows determination of their morphologies or manufacturing techniques, but also measurement of growth ring widths. We have applied XRCT to a selection of 38 mummy labels. This funerary furniture, made up of endemic or imported tree species, has survived thanks to environmental conditions in very large quantities in regions in Middle and Upper Egypt and is featured now in museum collections across the globe. Mummy labels thus represent a unique and abundant data source to build floating or absolutely dated dendrochronological chronologies for this period. Here we discuss the possible contributions and limitations of XRCT for the analysis of these artifacts and show that the approach allows identification of discriminating markers for the identification of certain species on the transverse plane, but that the insufficient resolution of the tangential and radial planes normally prevents formal identification of species. By contrast, XRCT undeniably enhances the visibility of toolmarks (in terms of numbers and depth), and thereby allows highlighting marks that remain invisible to the naked eye; XRCT also provides key insights into cutting methods and the calibers used and yields new information on silvicultural practices and the knowhow of Egyptian craftsmen. Finally, the measurement of ring widths on XRCT imagery is also more accurate than what can be achieved by traditional dendrochronological measurements, especially in the case of cuts realized on a slab. The approach also confirms the limited potential of local broadleaved species for dendrochronological approaches due to unreadable or poorly visible tree rings and mostly short tree-ring sequences., Competing Interests: NO authors have competing interests., (Copyright: © 2024 Blondel et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Over large regions exposed to natural disasters, cascading effects resulting from complex or concatenated natural processes may represent a large portion of total risk. Populated high-mountain environments are a major concern, and methods for large-scale quantitative risk analyses are urgently required to improve risk mitigation. This article presents a comprehensive quantitative rockfall risk assessment over a large archetypal valley of the Andean mountains, in Central Chile, which integrates a wide spectrum of elements at risk. Risk is expressed as an expected damage both in monetary terms and casualties, at different scales relevant for decision making. Notably, total rockfall risk is divided into its main drivers, which allows quantifying seismically induced rockfall risk. For this purpose, the local seismic hazard is quantified and the yield acceleration, that is, acceleration required to initiate rockfall, is determined at the regional scale. The probability of failure is thereafter derived in terms of annual frequency of rockfall initiation and integrated in the quantitative risk assessment (QRA) process. Our results show the significant role of seismic activity as the triggering mechanism of rockfalls, and highlight elements at risk that have a major contribution to the total risk. Eventually a sensitivity analysis is conducted to (i) assess the robustness of obtained risk estimates to the data and modeling choices and (ii) identify the most influential assumptions. Our approach evidences the feasibility of large-scale QRAs in sensitive environments and opens perspectives for refining QRAs in similar territories significantly affected by cascading effects and multihazards., (© 2023 Society for Risk Analysis.)

Explosive volcanism is a key contributor to climate variability on interannual to centennial timescales 1 . Understanding the far-field societal impacts of eruption-forced climatic changes requires firm event chronologies and reliable estimates of both the burden and altitude (that is, tropospheric versus stratospheric) of volcanic sulfate aerosol 2,3 . However, despite progress in ice-core dating, uncertainties remain in these key factors 4 . This particularly hinders investigation of the role of large, temporally clustered eruptions during the High Medieval Period (HMP, 1100-1300 CE), which have been implicated in the transition from the warm Medieval Climate Anomaly to the Little Ice Age 5 . Here we shed new light on explosive volcanism during the HMP, drawing on analysis of contemporary reports of total lunar eclipses, from which we derive a time series of stratospheric turbidity. By combining this new record with aerosol model simulations and tree-ring-based climate proxies, we refine the estimated dates of five notable eruptions and associate each with stratospheric aerosol veils. Five further eruptions, including one responsible for high sulfur deposition over Greenland circa 1182 CE, affected only the troposphere and had muted climatic consequences. Our findings offer support for further investigation of the decadal-scale to centennial-scale climate response to volcanic eruptions., (© 2023. The Author(s).)

Introduction: Mean xylem vessel or tracheid area have been demonstrated to represent powerful proxies to better understand the response of woody plants to changing climatic conditions. Yet, to date, this approach has rarely been applied to shrubs., Methods: Here, we developed a multidecadal, annually-resolved chronology of vessel sizes for Rhododendron ferrugineum shrubs sampled at the upper shrubline (2,550 m asl) on a north-facing, inactive rock glacier in the Italian Alps., Results and Discussion: Over the 1960-1989 period, the vessel size chronology shares 64% of common variability with summer temperatures, thus confirming the potential of wood anatomical analyses on shrubs to track past climate variability in alpine environments above treeline. The strong winter precipitation signal recorded in the chronology also confirms the negative effect of long-lasting snow cover on shrub growth. By contrast, the loss of a climate-growth relation signal since the 1990s for both temperature and precipitation, significantly stronger than the one found in radial growth, contrasts with findings in other QWA studies according to which stable correlations between series of anatomical features and climatic parameters have been reported. In a context of global warming, we hypothesize that this signal loss might be induced by winter droughts, late frost, or complex relations between increasing air temperatures, permafrost degradation, and its impacts on shrub growth. We recommend future studies to validate these hypotheses on monitored rock glaciers., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Piccinelli, Francon, Corona, Stoffel, Slamova and Cannone.)

Tree rings form the backbone of high-resolution palaeoclimatology and represent one of the most frequently used proxy to reconstruct climate variability of the Common Era. In the European Alps, reconstructions were often based on tree-ring width (TRW) and maximum latewood density (MXD) series, with a focus on European larch. By contrast, only a very limited number of dendroclimatic studies exists for long-lived, multi-centennial Pinus cembra, despite the widespread occurrence of the species at treeline sites across the European Alps. This lack of reconstructions can be ascribed to the difficulties encountered in past studies in extracting a robust climate signal from TRW and MXD chronologies. In this study, we tested various wood anatomical parameters from P. cembra as proxies for the reconstruction of past air temperatures. To this end, we measured anatomical cell parameters and TRW of old-growth trees from the God da Tamangur forest stand, known for being the highest pure, and continuous P. cembra forest in Europe. We demonstrate that several wood anatomical parameters allow robust reconstruction of past temperature variability at annual to multidecadal timescales. Best results are obtained with maximum latewood radial cell wall thickness (CWTrad) measured at 40 μm radial band width. Over the 1920-2017 period, the CWTrad chronology explains 62 % and >80 % of interannual and decadal variability of air temperatures during a time window corresponding roughly with the growing season. These values exceed those found in past work on P. cembra and even exceed the values reported for MXD chronologies built with L. decidua and hitherto considered the gold standard for dendroclimatic reconstructions in the European Alps. The wood anatomical analysis of P. cembra records therefore unveils a dormant potential and opens new avenues for a species that has been considered unsuitable for climate reconstructions so far., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

The Arctic is warming faster than any other region on Earth. Putting this rapid warming into perspective is challenging because instrumental records are often short or incomplete in polar regions and precisely-dated temperature proxies with high temporal resolution are largely lacking. Here, we provide this long-term perspective by reconstructing past summer temperature variability at Yamal Peninsula - a hotspot of recent warming - over the past 7638 years using annually resolved tree-ring records. We demonstrate that the recent anthropogenic warming interrupted a multi-millennial cooling trend. We find the industrial-era warming to be unprecedented in rate and to have elevated the summer temperature to levels above those reconstructed for the past seven millennia (in both 30-year mean and the frequency of extreme summers). This is undoubtedly of concern for the natural and human systems that are being impacted by climatic changes that lie outside the envelope of natural climatic variations for this region., (© 2022. The Author(s).)

Snow is highly sensitive to atmospheric warming. However, because of the lack of sufficiently long snow avalanche time series and statistical techniques capable of accounting for the numerous biases inherent to sparse and incomplete avalanche records, the evolution of process activity in a warming climate remains little known. Filling this gap requires innovative approaches that put avalanche activity into a long-term context. Here, we combine extensive historical records and Bayesian techniques to construct a 240-y chronicle of snow avalanching in the Vosges Mountains (France). We show evidence that the transition from the late Little Ice Age to the early twentieth century (i.e., 1850 to 1920 CE) was not only characterized by local winter warming in the order of +1.35 °C but that this warming also resulted in a more than sevenfold reduction in yearly avalanche numbers, a severe shrinkage of avalanche size, and shorter avalanche seasons as well as in a reduction of the extent of avalanche-prone terrain. Using a substantial corpus of snow and climate proxy sources, we explain this abrupt shift with increasingly scarcer snow conditions with the low-to-medium elevations of the Vosges Mountains (600 to 1,200 m above sea level [a.s.l.]). As a result, avalanches migrated upslope, with only a relict activity persisting at the highest elevations (release areas >1,200 m a.s.l.). This abrupt, unambiguous response of snow avalanche activity to warming provides valuable information to anticipate likely changes in avalanche behavior in higher mountain environments under ongoing and future warming., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794-2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in their mean, variance, amplitude, sensitivity, and persistence, the ensemble members demonstrate the influence of subjectivity in the reconstruction process. We therefore recommend the routine use of ensemble reconstruction approaches to provide a more consensual picture of past climate variability.

Recently revised ice core chronologies for Greenland have newly identified one of the largest sulfate deposition signals of the last millennium as occurring between 1108 and 1113 CE. Long considered the product of the 1104 CE Hekla (Iceland) eruption, this event can now be associated with substantial deposition seen in Antarctica under a similarly revised chronology. This newly recognized bipolar deposition episode has consequently been deemed to reveal a previously unknown major tropical eruption in 1108 CE. Here we show that a unique medieval observation of a "dark" total lunar eclipse attests to a dust veil over Europe in May 1110 CE, corroborating the revised ice-core chronologies. Furthermore, careful evaluation of ice core records points to the occurrence of several closely spaced volcanic eruptions between 1108 and 1110 CE. The sources of these eruptions remain unknown, but we propose that Mt. Asama, whose largest Holocene eruption occurred in August 1108 CE and is credibly documented by a contemporary Japanese observer, is a plausible contributor to the elevated sulfate in Greenland. Dendroclimatology and historical documentation both attest, moreover, to severe climatic anomalies following the proposed eruptions, likely providing the environmental preconditions for subsistence crises experienced in Western Europe between 1109 and 1111 CE.

The Eldgjá lava flood is considered Iceland's largest volcanic eruption of the Common Era. While it is well established that it occurred after the Settlement of Iceland (circa 874 CE), the date of this great event has remained uncertain. This has hampered investigation of the eruption's impacts, if any, on climate and society. Here, we use high-temporal resolution glaciochemical records from Greenland to show that the eruption began in spring 939 CE and continued, at least episodically, until at least autumn 940 CE. Contemporary chronicles identify the spread of a remarkable haze in 939 CE, and tree ring-based reconstructions reveal pronounced northern hemisphere summer cooling in 940 CE, consistent with the eruption's high yield of sulphur to the atmosphere. Consecutive severe winters and privations may also be associated with climatic effects of the volcanic aerosol veil. Iceland's formal conversion to Christianity dates to 999/1000 CE, within two generations or so of the Eldgjá eruption. The end of the pagan pantheon is foretold in Iceland's renowned medieval poem, Vǫluspá ('the prophecy of the seeress'). Several lines of the poem describe dramatic eruptive activity and attendant meteorological effects in an allusion to the fiery terminus of the pagan gods. We suggest that they draw on first-hand experiences of the Eldgjá eruption and that this retrospection of harrowing volcanic events in the poem was intentional, with the purpose of stimulating Iceland's Christianisation over the latter half of the tenth century.