Adding to the existing network of tree-ring chronologies in Scandinavia, Scots pine (Pinus sylvestris L.) trees at similar to 750 m a.s.l. in western Norway were used to derive a record, AD 1252-2008, of maximum latewood density by X-ray densitometry. Based on significant correlation to mean April-September temperature, a reconstruction explaining 56% of the variability over the AD 1900-2008 calibration period was made for southern Norway, with correlations >0.7 for the westernmost regions. A drop in inter-series correlation and replication in the early fifteenth century suggests that the reconstruction is most robust from ca AD 1450 onward. On decadal timescales, the warmest reconstructed temperatures are in the last half of the twentieth to the twenty-first centuries and cool periods were reconstructed in the mid-to-late fifteenth century, in the early seventeenth century, in the late seventeenth and early eighteenth centuries, in the late eighteenth century and in the mid-nineteenth century. When comparing to tree-ring widths from the same site, diverging centennial trends are indicated by ensemble empirical mode decomposition analysis. More samples are needed to investigate this more closely. Annual to multidecadal scale agreement with other tree-ring density temperature reconstructions in Fennoscandia, especially those from central Sweden, indicates that the reconstruction is a reasonable representation of regional temperature variability in large parts of southern Norway.
This work presents a spatiotemporal analysis of 5729 individual end-of-summer snowline altitude (SLA) observations. These data points were derived from manual mapping of 2257 glaciers across four periods (1977, 1994, 2009, and 2019) in the trans-Himalayan region of Ladakh. The study shows that snowline altitudes (SLAs) have risen on over 85% of glaciers investigated. The average SLA changed from a slight decrease of -0.93 m a(-)& sup1; between 1977 and 1994 to an increase of +8.47 m a(-)& sup1; between 2009 and 2019. Rising SLAs were accompanied by a 0.03 degrees C a-1 increase in regional mean annual air temperature between 1979 and 2019. Spatial variability in the rate of SLA change from basin to basin suggests that the sensitivity of glacier SLAs to the general rise in temperature is modulated by other climate factors, such as proportions of solid vs. liquid precipitation. Our analysis reveals that in the Suru and Zanskar basins, the regional mean SLA has risen to a level that now exceeds the maximum elevation of approximately 15% of the investigated glaciers. In these cases, the snowline has overshot glacier highest elevations by up to 350 m, effectively eliminating their accumulation zones. Thus, these ice masses have a negative mass balance and, no longer sustainable under current climatic conditions, will disappear.
Grain was the most important food source in pre-industrial Sweden. Climate variability is known to have affected grain harvests, but knowledge of Swedish climate-harvest relationships remains patchy prior to the late 19th century. In this study, we conducted statistical and geostatistical analyses of the effects of climate variability on harvest variations across Sweden for the main crops of spring barley and oats and winter rye over the period 1665-1810. We employed parish-level data from tithes, a tax levied on a certain percentage of the harvest, and state-of-the-art palaeoclimate reconstructions and reanalysis data. Geographically consistent positive relationships between summer temperatures and harvests are found in approximately the northern two-thirds of Sweden. This relationship extended further south for rye. Conversely, summer temperatures showed a negative relationship with the harvest of all three grain types in southern Sweden. For barley and oats, this negative relationship also extended throughout central Sweden. Higher May-July precipitation and higher soil moisture improved harvests in all but northern Sweden, and did so to a surprisingly comparable degree in wetter western as well as in drier eastern Sweden. The worst harvest outcomes were observed either during years of extremely dry conditions, very high June-July temperatures or extremely cold summers. In conclusion, climate-harvest relationships during the 1665-1810 period are surprisingly similar to those of today for the same crops and regions. Drought, rather than too low growing season temperatures, was the main constraint on grain cultivation in the major grain-growing regions of Sweden-even during the Little Ice Age.
Atmospheric CO2 rose by approximately 75-90 ppm during the last deglaciation (22,000 years BP to present), but the relative contributions of oceanic and terrestrial sources remain incompletely constrained. While the deep ocean is considered the primary contributor, it cannot account for the entire increase, implying additional terrestrial carbon fluxes. Here, changes in soil organic carbon (SOC) storage in tropical montane forests (TMFs) are quantified by analyzing deglacial warming effects on organic layer thickness using an empirically derived temperature-thickness relationship combined with paleoclimate model outputs. Monte Carlo uncertainty analysis reveals that global TMF organic layers thinned substantially from the Last Glacial Maximum to present, with total carbon storage declining to contribute an equivalent release of 1.5 ppm atmospheric CO2 after accounting for ocean buffering. These findings identify tropical montane forest soils as a previously unrecognized terrestrial carbon source during deglaciation, analogous to permafrost thaw rather than a carbon sink like peatland accumulation. Sensitivity analysis demonstrates that uncertainty in the empirical temperature-organic layer relationship dominates total uncertainty, highlighting the need for expanded calibration datasets across diverse tropical montane environments. The results underscore the vulnerability of tropical montane forest carbon stocks to ongoing climate warming and their potential role as a positive feedback in the global carbon cycle.
Snowpatches play a key role in alpine and high latitude environments and are highly vulnerable to climate change, particularly where there is no nival zone where they and dependent vegetation communities can retreat. We used a mix-methods approach, centred around satellite and snow course data, to identify and understand long-term trends and changes in persistence for 43 snowpatches in South-eastern Australia. Additionally, an eXtreme Gradient Boosting (XGBoost) model with SHapley Additive exPlanations (SHAP) analysis was applied, proving highly effective in identifying and ranking key predictors of snowpatch persistence. Results demonstrate the relative importance of spatial rather than temporal factors, and of the importance of fetch, elevation, peak snow depth, snow metre days, and ablation season temperature. We attribute the long-term decline in snowpatch persistence to global warming induced changes in the regional climate, with fluctuations in inter-annual variability in persistence caused by complex interactions between climate drivers. Applying changes in the mean day of year ablation date for surveyed snowpatches to the preferred snow cover ranges of snowpatch dependent vegetation communities is shown as an effective means to show potential changes in these communities over time, and through imputation of snowpatch melt date into the future, of probable impending impacts.
Source basin lithology plays a vital role in shaping alluvial fan morphology, yet such studies are limited, often contradictory, and based on small datasets. This study quantitatively examines 173 fan-basins in the Spiti Valley cold desert (India), where similar climatic and tectonic conditions, but varied lithologies (six groups), provide an ideal setting for such a study. An integrated remote sensing and field approach, with proxies, such as ideal fan-area (Afi), slope of ideal fan (Sfi), selective basin-area (Abs), and lithology-specific angle of repose (to estimate sediment generation/storage), was employed. Results from morphometric analyses indicate that lithology strongly governs fan morphology, with clearer relationships emerging through lithological-group-wise analyses, despite weak correlations for the entire dataset. Erodible lithologies (shale-dominated) form small, steep fans under confined settings but create larger, flatter fans as basin-area and slope increase. Resistant lithologies (high-grade metamorphic and crystalline rocks) consistently produce small, steep fans due to limited sediment supply, while sandstone-dominated rocks generate larger, gentler fans. Limestone and mixed lithologies produce intermediate forms. Irrespective of basin-lithology, basins dominated by glacial processes produce the largest and gentlest fans through effective sediment transport. Basin-slope vis-& agrave;-vis angle of repose serves as a useful proxy for sediment dynamics but requires cautious application. Finally, confinement and depositional processes significantly modify fan-morphology, making Afi and Sfi more reliable indicators of lithology-fan relationships.
The classical paradigm of glacial cirque evolution, centered on glacial erosion, often underestimates the contribution of interglacial periods. This study quantitatively assesses the role of paraglacial (rock-slope failures, RSF) and periglacial (scree) processes in the morphogenesis of eight Quaternary cirques in Vestfir & eth;ir, Iceland. The methodology relies on building a Holocene reference model by quantifying the current volumes of cirques and their internal RSF (61.5%) and scree deposits (38.5%). This model is then extrapolated over 22 Quaternary interglacial cycles. The Quaternary extrapolation reveals a continuum of morphogenic controls: in smaller cirques, interglacial processes can account for the majority of the excavated volume, whereas larger cirques are dominated by glacial erosion. This highlights a scale effect. These findings challenge the traditional glacial-centric view and support a positive-feedback model where glacial and interglacial processes act in a synergistic relationship, driving cirque widening over successive climatic cycles. The study thus re-evaluates the role of interglacial slope dynamics as a crucial, and sometimes primary, agent in cirque development.
Late Quaternary climate change and the associated glacio-fluvial dynamics, especially in the high-altitude Himalayan region, are major scientific concerns. The Parbati River basin, located in the Kullu district, is highly vulnerable to changing temperature patterns and associated snow cover dynamics, including Glacial Lake Outburst Floods (GLOFs), glacial retreats, and avalanches. The current study examined the assessment of snow-covered areas (SCA) using the Normalized Difference Snow Index (NDSI) and temperature dynamics, as measured by Land Surface Temperature (LST), which relies primarily on Landsat imagery from 2003 to 2023. The research revealed a strong negative correlation between LST and NDSI, with an increase in LST from -42 degrees C in 2003 to -13 degrees C in 2023 leading to a drastic decline in snow cover, at a rate of -31.85 square kilometres per year between 2003 and 2023. Furthermore, this region exhibited a sharp shift in the snowline position, from 123.05 m/year in 2003 to 2023. The outcome is crucial for illustrating the effects of climate change on highly mountainous, snow-covered basins.
The rapid retreat of mountain glaciers and the formation of new glacial lakes due to climate change pose considerable risks in mountain regions, especially where they increase the frequency and magnitude of glacial-lake outburst floods (GLOFs) and J & ouml;kulhlaups. This study presents an integrated inventory of glacial lakes in the Hindukush-Region of Afghanistan (HKA) for 2020 and the first multi-decadal assessment (1990-2020) of glacial lake changes. For 2020, we identified 2596 glacial lakes and supra-glacial ponds with an area of 96.8 +/- 14.8 km(2) (2362 lakes >= 0.003 km(2) and 234 smaller lake/ponds < 0.003 km(2)). This indicates an increase of 32% by number and 21% by area since 1990. We analyzed lake formation, expansion, decline and disappearance and found that patterns of change vary significantly between regions and as a function of altitude. 56% of lakes expanded, 20% shrunk, 17% were newly formed and 6% disappeared between 1990-2020. Glacial lakes in the HKA begin at similar to 2980 m-asl, and the rate of increase of lake area was greatest for the elevation range 5300-5800 m-asl, during 2010-2020. Whilst lakes were generally increasing in area, those in the southwestern region of the HKA were decreasing, mainly because they were associated with smaller glaciers that were in a drier region. Smaller lakes (<= 0.01-0.05 km(2)), particularly ice-contact proglacial lakes showed rapid increases, whereas larger lakes (>1.0 km(2)) tended to decrease in size. This study reveals the importance of considering geographical and altitudinal variation in glacial-lake formation and the role of smaller-lakes in GLOF-formation and water resources.
Justin D. Schove was well before his time when he published his climate reconstruction for northern Scandinavia (1461-1938 CE) in Geografiska Annaler 1954. At this time, there was an interest in understanding the global temperature increase that had been observed in the 1920s to 1950s. Aiming to extend the 'thermometric indices' well before the instrumental observations begun, Justin D. Schove combined five tree-ring width chronologies from northern Norway and Sweden into a northern Scandinavian temperature index (NSTI). The NSTI was regarded as an index of regional May-August temperatures and it was (i) evaluated against various seasonal weather characteristics and observed temperatures from Europe; (ii) argued that the NSTI, together with documentary evidence, could provide information about the atmospheric circulation; and (iii) shown that, in general, years with very narrow annual rings corresponded to documentary evidence on failed harvests and famines. Overall, the synthesis presented by Schove preceded by many decades more focused research efforts using tree rings in the Nordic countries and elsewhere; clearly, he was a dendroclimatological visionary.
Alderney in the Channel Islands (W Europe) was never glaciated during the Quaternary but rather has been affected by long-term weathering of the underlying igneous and metamorphic rocks. This study investigates the evidence for weathering and sediment generation under mainly cold Quaternary climatic conditions, based on (1) surface geomorphology, (2) Schmidt hammer rebound values on bedrock outcrops, and (3) sediment stratigraphy along coastal sections where weathering-derived solifluction slope sediments are exposed by erosion. Results show the dominance of cold-climate features across the landscape, reflecting the role of late Quaternary periglacial weathering in producing and then mobilizing slope sediments. Both slope stratigraphy and evidence from Schmidt hammer data suggest several phases of weathering activity, but their precise timing is not yet known. Although changes in Quaternary climate (temperature, humidity) and sea level are the most likely drivers for both weathering and slope sediment supply, it is likely that this was not a simple relationship, for example, where there is progressive infilling of slope accommodation space over time. Investigating the relationships between weathering (sediment generation) and slope (sediment deposition) processes, constrained by radiometric dating, offers the best framework for understanding the development of non-glaciated landscapes in western Europe.
The Taklimakan Desert is the largest desert in China. High temperatures pose a deadly threat to the fragile ecosystems in the desert, but the long-term temperature changes are unclear, which seriously affects the decision-making on desert control and ecological restoration. This study constructed a tree-ring width chronology of Populus euphratica in the lower Tarim River to investigate the impact of surface air temperature (SAT) and ground surface temperature (GST) on the growth of P. euphratica. Correlation analysis indicated that high summer temperatures significantly inhibit the growth of P. euphratica, especially high GST. On this basis, we reconstructed the GST from May to July in the lower Tarim River over the past 188 years. The reconstruction explained 52.7% of the variance in observed data and revealed a significant warming trend starting from the 1940s. The combination of reconstruction and observational data revealed that changes in GST in the past 20 years have exceeded the range of variation in the past 200 years and that GST is increasing at a rate far exceeding SAT in recent decades. Analysis showed that Atlantic Multidecadal Oscillation (AMO), circumglobal teleconnection (CGT) and westerly winds are the main drivers of GST changes in the eastern Taklamakan Desert. AMO affected the CGT wave train on the interdecadal scale and thus affected the GST. This study reveals the impact of GST on tree growth in the desert and the possible driving mechanisms of GST changes in the Tarim Basin, which should guide the desert's ecological restoration and climate prediction.
Vegetation-banked terraces (VBTs) with bare treads and vegetated risers occur in periglacial environments characterized by strong winds, shallow ground freezing and frequent freeze-thaw cycles. On lee slopes on Scottish mountains they follow the contour, but as exposure to dominant winds increases they dip windward. Comparative analyses of VBTs on mountains with non-frost-susceptible regolith cover and those on mountains with frost-susceptible soils reveal significant differences in dimensions, associated landforms and current activity. The former are generally smaller, lack over-ridden organic material and are associated with aeolian landforms and deposits. They are apparently static features where present activity is limited to needle-ice creep of debris across terrace treads and over risers. The latter are associated with active vegetation-covered solifluction terraces, have over-run organic material and are currently moving en masse downslope through frost creep and possibly gelifluction. We infer that VBTs on non-frost-susceptible regolith cover formed through the accumulation of debris at the upslope margins of wind stripes that formed due to wind erosion during the Little Ice Age. The latter probably represent Holocene vegetation-covered solifluction terraces from which vegetation has been stripped from treads by turf exfoliation (disruption by needle ice, deflation of fines and undermining of soil scarps).
Viscous creep features in perennially frozen, ice-supersaturated talus/debris, usually called 'rock glaciers', are characteristic phenomena of mountain permafrost. On behalf of the Global Network for Permafrost (GTN-P) as part of the Global Climate Observing System (GCOS), the International Permafrost Association (IPA) has developed an initiative to systematically inventory them at global scale, and to monitor their kinematics. Corresponding consensus-based guidelines (RGIK 2023) define precise mapping procedures underpinned by facts and physics-based concepts concerning the involved conditions, material properties, processes and spatiotemporal scales. The related, more or less complex landsystem relations are treated in a strictly objective/descriptive sense as spatial upslope connections or neighbourhood situations. Application of such principles helps with avoiding misinterpretations and confusion sometimes induced with direct, intuitive, genetic attribution of landform 'origins'. This is illustrated for a case in Nuristan, eastern Hindu Kush, Afghanistan, where in-situ measurements are lacking. Permafrost can confidently be inferred to be abundant in the region. Numerous, often spectacular, millennia old, and still actively advancing rock glaciers can be recognized and clearly distinguished from down-wasting (debris-covered) glaciers. Comparison with long-term creep in permafrost at Galena Creek (Absaroka Mountains) and Gruben (Swiss Alps), where in-situ measured facts are available, confirm that the international guidelines for related inventorying and mapping are fully adequate and should strictly be adhered to.
Despite significant efforts to reconstruct the Holocene glacial history in Scandinavia, evidence of glacier fluctuations in Sweden has mostly been limited to palaeoclimatic proxies, while dating of direct geological evidence from glacier forelands is still rare. This is the first study in Sweden that has attempted to fully reconstruct dynamics, chronology and palaeoclimate of a glacier throughout the Holocene by applying geomorphological mapping, sedimentology, lichenometry and Equilbrium Line Altitude (ELA) calculation on Helagsglaci & auml;ren, Sweden's southernmost glacier. Helags valley is occupied by extensive glacial and associated sediments of different ages far beyond the current extent of the glacier, indicating earlier prominent advances dated here to 8.5-8.0 ka, around 1.2-1.0 ka and around 1789 CE, which represents the Little Ice Age (LIA) maximum. During the Holocene, the glacier switched from a polythermal regime with frozen bed at the thinning ice margin and parts of the tongue to a fully temperate one. Today, its southern part remains active and temperate, while the northern is probably cold-based. Using calculated ELAs, the climate during the 8.5-8.0 ka event was reconstructed to be cold and wet; slightly colder and drier during the 1.2-1.0 ka advance; and coldest and driest during the LIA. This agrees well with other paleoclimate and glacier fluctuation reconstructions from Scandinavia. In conclusion, this study demonstrates a wealth of information on past glacier dynamics and palaeoclimate that can be reconstructed from current small cirque glaciers in the Swedish Scandinavian Mountains, highlighting the need to study them more extensively.
A comprehensive understanding of the intricate relationship between precipitation threshold and extreme river discharge, especially in mountainous regions, is challenging yet crucial for effective mountain risk management. This study, conducted in the Himalayan region of Nepal, employs an innovative approach using Intensity-Duration-Frequency (IDF) curves to identify potential precipitation extremes relevant to extreme river discharges. Detailed analysis of historical hydrometeorological events and their impacts in Nepal was carried out to select a specific event for thorough examination. Additionally, the research evaluates satellite-based precipitation data and utilizes frequency analysis techniques such as Gumbel and Log Pearson Type III distributions, customized to the region's unique conditions. Furthermore, the study evaluates Probable Maximum Precipitation (PMP) and Depth-Area-Duration (DAD) curves at various sub-basin levels. The findings underscore the significant role of 3-day consecutive precipitation over 1-day events in generating extreme river discharge within the basin. Notably, the study reveals discrepancies between PMP values derived from gauge-based and satellite-based data, emphasizing the necessity for proper bias correction of the satellite data. Despite its limitations, the research highlights the potential of high-resolution satellite data for disaggregating gauge observed daily precipitation and underscores its applicability to other Himalayan basins, offering valuable insights into precipitation-related extreme events and their implications for water resource management and disaster risk reduction.
Morphometric analysis of previously unresearched tributary junction fans (TJFs) of the Spiti valley cold desert, India, was conducted to understand the factors influencing their development. An integrated remote sensing and field approach was employed, including the development of multi-method morphometric indices viz. fan conicality (FCI), sweep angle (SA), fan width-to-length ratio (W/L), feeder stream-order and valley floor width-to-height ratio (Vf). Such TJFs, which are the most suitable cultivation and settlement sites in this region, were found to be largely polygenic and planimetrically confined, with many being multi-staged in terms of their development. The results of morphometric analyses reveal that the TJFs are relatively smaller but steeper than their counterparts in other settings, with high relative topographic confinement causing the construction of smaller and steeper fans. The competence of the feeder stream, along with associated processes, notably influences fan morphology using differential sediment transporting capacity. TJFs created by more competent streams are less steep, more influenced by topographic confinement and more vulnerable to truncation by the trunk stream. Furthermore, tectonically induced base-level fall and resultant downcutting in confined environments have caused the formation of truncated, multi-staged and entrenched fans and are primarily responsible for coupling between TJF catchments and trunk stream in the study area.
Characterization of landslide susceptibility carries great importance in hilly regions as it is one of the frequently occurring natural hazards which comes with huge destruction of life as well as property. Identification of such landslide susceptible zones is usually decided based on the necessity and available resources. It is considered a valuable input for planning developmental activities by policymakers. The current study focuses on Pabbar Catchment, located in the state of Himachal Pradesh in India and prepares a Landslide Susceptibility Map (LSM) at a catchment scale using Analytical Hierarchy Approach (AHP). Eleven geo-morphological attributes of the catchment called causative factors were used in thematic form while creating the LSM. Being a semi-quantitative method, AHP performed satisfactorily to produce a realistic distribution of landslide susceptibility with a prediction accuracy of 0.768 under the Area Under Curve (AUC) technique. Approximately 72% of the geographical area from the catchment falls under the 'high' landslide susceptible zone. Unavailability of LSM at this scale is addressed through this study that may be useful to regional planners for future land use planning.
Topographical changes in riverine floodplains need to be measured for assessing geomorphological dynamics and protecting floodplain areas, although topographic evaluation in disaster-prone floodplain in South Asia has been limited due to the lack of multitemporal, high-definition digital elevation models (DEMs) derived from modern techniques including airborne laser scanning, structure-from-motion (SfM) photogrammetry accompanied with Unmanned Aerial Vehicle (UAV, often referred as drone), and field-based mapping approaches. Here we conducted a preliminary study at two locations of Teesta River (Brahmaputra's tributary) in Bangladesh using the UAV-SfM techniques and generated high-resolution DEMs. The selected locations represent dynamic changes of sediment and water on the floodplain over the years, and the UAV-SfM approach can be an effective method for monitoring those changes, but an archive of the past data has been unavailable. Here we evaluated the topographic changes by comparing the UAV-SfM-derived DEMs of 2022 with global DEM products (NASADEM of 1999), which are often the only available choice of DEMs in this river floodplain. The elevation differences of these two sets of DEMs were in the range of -5.23 to -84.66 m, and volumetric changes of -4.11 +/- 0.15 to -86.25 +/- 0.20 million m3, likely dominated by erosional processes towards the left side bank where the elevation errors are supposed to be several meters for UAV-DEM and ca. 5-12 m for NASADEM. Although it is not easy to accurately evaluate the absolute values of the changes, these changes may be associated with the upper basin's morphodynamics.
Mountain snowline dynamics are relatively underreported with few studies exploring spatial snowline dynamics. Whilst clear regional-scale relationships between snowline location and temperature exist in European mountains, recent research at higher latitudes reports no response to climate change. In maritime mountains, snowlines occupy complex environmental gradients. Using timeseries of satellite data from Landsat missions 5-8 (151 images between 1984 and 2021), we explored sub-regional summer snowline dynamics across the maritime-continental climate gradient in the Western Norwegian mountains. We characterize spatio-temporal snowline altitude dynamics and investigate the climate factors altering snowline patterns. Summer snowline altitudes were found to increase inland at around double the rate of the 0 degrees C summer isotherm. Data from the European Centre for Medium-Range Weather Forecasts (ECMWF) land component of the fifth generation of European Reanalysis (ERA5-Land), showed a potential 'maritime-mountain' effect with coastal orographic snowfall and cloud cover-induced surface solar downwelling radiation amplifying maritime-continental snowline altitude gradients alongside surface atmospheric temperature. This was replicated in the Canadian Rocky Mountains. Between 1984 and 2021, we found spatial summer snowline gradients in Norway decreased and propose multiple climate forcings are responsible, potentially masking links between snowlines and climate change. Although non-significant, the data also suggest regional summer snowline altitudes increased. This study demonstrates the complex spatial heterogeneity in snow-climate relationships and highlights how long-term snow dynamics can be queried using fine-grain (Landsat) resolution satellite data. We share our approach through a Google Earth Engine web-app that rapidly executes spatial snowline analyses for global mountain regions via a graphical user interface.
