Winter Snow Research Articles

Quantifying the effect of freeze-thaw cycles on track surface deformation and degradation of railway track geometry; Case study

Freeze-thaw cycles (FTC) are known to have an effect on railway track stability, safety, and performance. FTC are expected to become more frequent in the future due to climate change. This paper presents the results of a field investigation in which the mechanism of FTC development within the track embankment and its effect on the performance of railway tracks including track surface deformation and track geometry degradation are studied. Field observations suggested that the frost depth within the track embankment is influenced by the freezing index and winter snow cover. They also showed that a warmer and drier winter leads to more intermittent FTC and even though the average frost heave is lower than for a colder winter, the frost heaves occurring at culvert locations creates a larger differential deformation and thus may lead to a worse operating condition. The comparison of geometry measurements before freezing and after thawing indicated that the track geometry is in poorer and rougher condition during springs that were preceded by increased FTC. It was also concluded that track in proximity to culverts suffered the highest geometry degradation. Overall, the limited field observations of this study suggest that future winters, mild with less precipitation and higher occurrence of FTC, may increase the rate of track deterioration and more maintenance will be required to keep track within safe limits.

OTIMIZAÇÃO DA REGULAÇÃO E CONTROLE DE LESÕES ESPORTIVAS E FADIGA DE ATLETAS DO GELO E DA NEVE NOS JOGOS OLÍMPICOS DE INVERNO COM BASE NA PREVENÇÃO DE LESÕES

ABSTRACT This study reveals the characteristics and relationship of sports injury and fatigue of the Winter Olympics athletes, and monitors the athletes’ psychological condition through case analysis of excellent athletes, and provides empirical evidence for athletes’ psychological training and preparation for the physical and mental health services of Winter Olympics. Through questionnaires, literature review and other methods to study the injury situation of Winter Olympics ice and snow athletes, the results show that the proportion of chronic lumbar and knee joint injuries, and repeated muscle strains of Chinese Winter Olympics ice and snow athletes is large, and the cure rate is not high. The preparation activities are neither paid enough attention or sufficient, and the rationality of training plan arrangement is insufficient. The main cause of injury is insufficient understanding of the mechanism of injury and illness among athletes and coaches. Individual elite athletes need to improve their coping skills and pay attention to their psychological fatigue. In view of the sports’ psychological characteristics and the problems faced by winter athletes, personalized psychological intervention programs should be formulated.

Ecological responses to variation in seasonal snow cover.

Seasonal snow is among the most important factors governing the ecology of many terrestrial ecosystems, but rising global temperatures are changing snow regimes and driving widespread declines in the depth and duration of snow cover. Loss of the insulating snow layer will fundamentally change the environment. Understanding how individuals, populations, and communities respond to different snow conditions is thus essential for predicting and managing future ecosystem change. We synthesized 365 studies that examined ecological responses to variation in winter snow conditions. This research encompasses a broad range of methods (experimental manipulations, measurement of natural snow gradients, and long-term monitoring), locations (35 countries), study organisms (plants, mammals, arthropods, birds, fish, lichen, and fungi), and response measures. Earlier snowmelt was consistently associated with advanced spring phenology in plants, mammals, and arthropods. Reduced snow depth often increased mortality or physical injury in plants, although there were few clear effects on animals. Neither snow depth nor snowmelt timing had clear or consistent directional effects on body size of animals or biomass of plants. However, because 96% of studies were from the northern hemisphere, the generality of these trends across ecosystems and localities is also unclear. We identified substantial research gaps for several taxonomic groups and response types; research on wintertime responses was notably scarce. Future research should prioritize examination of the mechanisms underlying responses to changing snow conditions and the consequences of those responses for seasonally snow-covered ecosystems.

Ephemeral gullies caused by snowmelt: A ten-year study in northeastern China

Ephemeral gully erosion of cultivated land may be serious in early spring because of snowmelt runoff and lack of vegetation cover during this period. The snow in winter is redistributed by winds and accumulates in low-lying gullies, furrows, forest shelterbelts and forest lands, which become the main source of snowmelt runoff in spring. This study selected three different hillslopes according to snow redistribution in the black soil region of northeastern China and investigated the ephemeral gully erosion caused by snowmelt runoff from 2009 through 2018. The results showed that drainage area was the main controlling factor of ephemeral gully development. Due to the influence of snow redistribution, volumetric soil loss of ephemeral gully erosion in cultivated hillslopes affected by forestland and forest shelterbelt were more than 2 times greater than that of cultivated hillslopes without other sources of snowmelt runoff. A snow redistribution factor, SR, calculated through surveyed snow depth, accounted for the influence of snow redistribution on ephemeral gully erosion. Ridge tillage increased the threshold value of runoff needed for initial formation of ephemeral gullies, and decreased the number of gullies formed, but it also accelerated the development of single ephemeral gullies once they formed because furrows accumulated more runoff feeding to the drainage areas. A tillage practice factor, T, was used to reflect the influence of ridge tillage on ephemeral gully erosion. A statistical model for estimating ephemeral gully volume was developed that included as independent variables snowfall (SN), snow redistribution factor (SR), drainage area (A) and tillage practice factor (T). Using these parameters, along with bulk density of soil (BD), soil loss (Mg) by ephemeral gullies was estimated to be 0.102*SN1.104*SR*A0.90 *T3.0 *BD (R2 = 0.76).

Hydraulic function and conduit structure in the xylem of five oak species

Abstract Many plant lineages, including oaks (Quercus spp.), have both vessels and tracheids as hydraulically conductive cells within their xylem. The structure of these co-occurring conduit types and their contribution to plant hydraulic function have been relatively little studied. We hypothesized that vasicentric tracheids contribute to hydraulic function under conditions of low water availability. We predicted that within a species, oaks growing at drier and warmer low elevation sites would have more tracheids and be more embolism resistant compared to those growing at moister and colder higher elevation sites. We also predicted that across species, lower elevation oaks would have increased tracheid abundance within their xylem. Five oak species differed in many xylem traits, including vessel diameter and length, tracheid size and abundance, embolism resistance, and hydraulic conductivity. Tracheids were most abundant in the xylem of the highest elevation species at sites that receive winter snow and freezing temperatures. Vessels were relatively vulnerable to embolism as confirmed with multiple methods, including centrifuge vulnerability curves, micro-CT scans of native stem samples, and single vessel air injection. Theoretical conductivity calculations indicated that tracheids account for 5.7–15.5% of conductivity in hydrated stems, with tracheids likely increasing in importance as large diameter vulnerable vessels embolize. The occurrence of both vessels and vasicentric tracheids in the xylem of oaks may enable them to function within highly seasonal climates. Tracheids, though often overlooked, may be particularly important in maintaining conductivity throughout much of the year when water potentials decline from seasonal maximums and following freeze-thaw events.

Insights into Particle-Bound Metal(loid)s in Winter Snow Cover: Geochemical Monitoring of the Korkinsky Coal Mine Area, South Ural Region, Russia

Snow plays an important role in air quality and winter geochemical monitoring in the South Ural region. This study deals with the air pollution monitoring of particle-bound metal(loid) concentrations using snow cover around the deepest coal mine in Eurasia, the Korkinsky coal mine. We studied the concentrations and ratios of suspended and dissolved forms of metal(loid)s (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Sr, and Zn) in snow samples. We examined 56 snow cover samples, collected at 12 sites located north, south, east and west of the Korkinsky coal mine. All snow samples were taken in January 2020. The spectral reflectance curves, cluster analysis, and spatial distribution maps were used to evaluate the potential sources of PM-bound metal(loid)s and the potential relationship among them. The highest concentrations (μg/L) were reported for Fe, Al, and Zn. In addition to the mine influence, burning coal for residential heating was identified as the major anthropogenic metal(loid) source. It was shown that elevated concentrations of some trace metals in snow samples were associated with southerly winds and the location of spoil heaps.

Factors Governing Winter Snow Accumulation and Ablation Susceptibility Across the Sierra Nevada, U.S.A.

AbstractSeasonal snow water equivalent (SWE) accumulation in California’s Sierra Nevada is primarily governed by a few orographically enhanced snowstorms. However, as air temperatures gradually rise, resulting in a shift from snow to rain, the governing processes determining SWE accumulation versus ablation become ambiguous. Using a network of 28 snow pillow measurements to represent an elevational and latitudinal gradient across the Sierra Nevada, we identify distributions of critical temperatures and corresponding storm and snowpack properties that describe how SWE accumulation varies across the range at an hourly timescale for water years 2010 through 2019. We also describe antecedent and prevailing conditions governing whether SWE accumulates or ablates during warm storms. Results show that atmospheric moisture regulates a temperature dependence of SWE accumulation. Conditions balancing precipitable water and snow formation requirements produce the most seasonal SWE, which was observed in the (low-elevation) northern and (middle-elevation) central Sierra Nevada. The high southern Sierra Nevada conservatively accumulates SWE with colder, drier air, resulting in less midwinter ablation. These differences explain a tendency for deep, low-density snowpacks to accumulate rather than ablate SWE during warm storms (having median temperatures exceeding 1.0°C), reflecting counteracting liquid storage and internal energy deficits. The storm events themselves in these cases are brief with modest moisture supplies or are otherwise followed immediately by ablation.

Analyses of Spatial and Temporal Variations of Salt Concentration in Waterbodies Based on High Resolution Measurements Using Sensors

Studies have shown that salt concentrations are increasing in waterbodies such as lakes, rivers, wetlands, and streams in areas where deicers are commonly applied for winter road maintenance, resulting in degraded water quality. As the salt concentration varies spatially and temporally based on environmental and hydrological characteristics, we monitored high resolution (15 min) salt concentrations for a relatively long period (winter and spring season) at different sites (i.e., stream, urban-stream, roadside drain, and parking-lot drain) using multiple electric conductivity-based sensors. The salt concentrations were significantly different from each other considering individual sensors and different sites in both winter and spring seasons, which support past research results that concentration varies spatially. Parking-lot (1136 ± 674 ppm) and Roadside (701 ± 263 ppm) drain measured significantly higher concentration than for Stream (260 ± 60 ppm) and Urban-stream (562 ± 266 ppm) in the winter season. Similar trends were observed for the spring season, however, the mean concentrations were lower in the spring. Furthermore, salt concentrations were significantly higher during the winter (242 ± 47 ppm to 1695 ± 629 ppm) than for the spring (140 ± 23 ppm to 863 ± 440 ppm) season considering different sites, which have been attributed to the winter snow maintenance practice using deicers in past studies. All sites exceed the United States Environmental Protection Agency (USEPA) threshold (salt concentration higher than 230 mg/L) for chronic exposure level for 59% to 94% and 10% to 83% of days in winter and spring seasons, respectively. The study has highlighted the usefulness and advantages of high resolution (spatially and temporally) salt concentration measurement using sensor technology. Furthermore, the salt concentration in waterbodies can vary spatially and temporally within a small spatial scale, which may be important information for managing water quality locally. The high resolution measurements (i.e., 15 min) were helpful to capture the highest potential salt concentrations in the waterbody. Therefore, the sensor technology can help to measure high resolution salt concentrations, which can be used to quantify impacts of high salt concentrations, e.g., application of deicer for winter road maintenance on aquatic systems based on the criteria developed by USEPA.

Cryogenic cave carbonates in the Dolomites (northern Italy): insights into Younger Dryas cooling and seasonal precipitation

Abstract. In the European Alps, the Younger Dryas (YD) was characterised by the last major glacier advance, with equilibrium line altitudes being ∼ 220 to 290 m lower than during the Little Ice Age, and also by the development of rock glaciers. Dating of these geomorphic features, however, is associated with substantial uncertainties, leading to considerable ambiguities regarding the internal structure of this stadial, which is the most intensively studied one of the last glacial period. Here, we provide robust physical evidence based on 230Th-dated cryogenic cave carbonates (CCCs) from a cave located at 2274 m a.s.l. in the Dolomites of northern Italy coupled with thermal modelling, indicating that early YD winters were only moderately cold in this part of the Alps. More precisely, we find that the mean annual air temperature dropped ≤ 3 ∘C at the Allerød–YD transition. Our data suggest that autumns and early winters in the early part of the YD were relatively snow-rich, resulting in stable winter snow cover. The latter insulated the shallow subsurface in winter and allowed the cave interior to remain close to the freezing point (0 ∘C) year-round, promoting CCC formation. The main phase of CCC precipitation at ∼ 12.2 ka coincided with the mid-YD transition recorded in other archives across Europe. Based on thermal modelling we propose that CCC formation at ∼ 12.2 ka was most likely associated with a slight warming of approximately +1 ∘C in conjunction with drier autumns and early winters in the second half of the YD. These changes triggered CCC formation in this Alpine cave as well as ice glacier retreat and rock glacier expansion across the Alps.

Seasonal Precipitation and Soil Moisture Relationships Across Forests and Woodlands in the Southwestern United States

AbstractPrecipitation [P: mm] controls forest and woodland dynamics in the southwestern United States (SWUS) by altering soil moisture [θ: mm3 mm−3] availability, but the influence of P on θ is complex, varying across space and time. We evaluated seasonal P and θ relationships at shallow (0–20 cm) and intermediate (50 cm) soil depths for nine semiarid forest and woodland sites (56 total years), which comprised three elevation gradients in the SWUS. We developed time‐varying definitions of winter (snow accumulation), spring (moisture recharge), and summer (moisture deficit), and determined how these sites exhibited similar P influence on θ across depths in the soil profile, between seasons, and in seasons with above‐ and below‐average P. Higher elevation sites (>2,800 m) experienced greater winter P, longer springs, and shorter summers compared to lower elevation sites (<2,500 m). Seasons with above‐ and below‐average P reduced elevation‐associated differences. θ at 0–20 cm was generally decoupled from θ at 50 cm in seasons with average and below‐average P, imparted by differences in spring and summer rainfall versus winter snowfall. Notably, across‐season influence of θ (e.g., a season’s similarity to subsequent seasons) was high when the first season experienced above‐ or below‐average P, and the subsequent season experienced average P, illustrating an important temporal connection initiated by wet and dry conditions. These results illustrate similarities in P‐θ relationships across widely differing ecosystems in the SWUS, and elucidate how these relationships may be altered in a changing climate.

Past and future snowmelt trends in the Swiss Alps: the role of temperature and snowpack

The start of the growing season for alpine plants is primarily determined by the date of snowmelt. We analysed time series of snow depth at 23 manually operated and 15 automatic (IMIS) stations between 1055 and 2555 m asl in the Swiss Central Alps. Between 1958 and 2019, snowmelt dates occurred 2.8 ± 1.3 days earlier in the year per decade, with a strong shift towards earlier snowmelt dates during the late 1980s and early 1990s, but non-significant trends thereafter. Snowmelt dates at high-elevation automatic stations strongly correlated with snowmelt dates at lower-elevation manual stations. At all elevations, snowmelt dates strongly depended on spring air temperatures. More specifically, 44% of the variance in snowmelt dates was explained by the first day when a three-week running mean of daily air temperatures passed a 5 °C threshold. The mean winter snow depth accounted for 30% of the variance. We adopted the effects of air temperature and snowpack height to Swiss climate change scenarios to explore likely snowmelt trends throughout the twenty-first century. Under a high-emission scenario (RCP8.5), we simulated snowmelt dates to advance by 6 days per decade by the end of the century. By then, snowmelt dates could occur one month earlier than during the reference periods (1990–2019 and 2000–2019). Such early snowmelt may extend the alpine growing season by one third of its current duration while exposing alpine plants to shorter daylengths and adding a higher risk of freezing damage.

Response of U.S. West Coast Mountain Snowpack to Local Sea Surface Temperature Perturbations: Insights from Numerical Modeling and Machine Learning

AbstractSea surface temperature (SST) significantly modulates the precipitation and temperature over land, with important consequences on land surface processes such as snowpack. Compared to the impact of remote SST, the effect of nearshore/local SST is less well understood. In this study, the impact of local SST on the mountain snowpack of the U.S. West Coast is investigated using two 6-km regional climate simulations driven by the same lateral boundary conditions but with time-varying versus time-invariant and warmer local SSTs during 2003–15. Results show that local SST warming leads to warmer winter with more precipitation over the mountains. Meanwhile, the removal of SST temporal variability results in reduced temperature variability but increased precipitation variability. As a result, winter snow accumulation decreases by ~200 mm per season in the Cascade Mountains in the north but increases by ~100 mm per season in the Sierra Nevada in the south. Such a dipole response results from the competing effects of precipitation and temperature change at different elevations and are amplified by the enhanced atmospheric river moisture transport. To further delineate the relative contributions of different meteorological factors to the snowpack response, two neural network models were developed to predict the snow behaviors at seasonal and monthly scales. These models reveal the dominant influence of the total amount and the average temperature of precipitation on the snowpack response. These findings highlight the sensitivity of mountain snowpack to local SST in the western United States and underscore the importance of local SST and atmospheric rives to accurate snowpack estimations for water management.

Tundra Type Drives Distinct Trajectories of Functional and Taxonomic Composition of Arctic Fungal Communities in Response to Climate Change - Results From Long-Term Experimental Summer Warming and Increased Snow Depth.

The arctic tundra is undergoing climate-driven changes and there are serious concerns related to the future of arctic biodiversity and altered ecological processes under possible climate change scenarios. Arctic land surface temperatures and precipitation are predicted to increase further, likely causing major transformation in terrestrial ecosystems. As a response to increasing temperatures, shifts in vegetation and soil fungal communities have already been observed. Little is known, however, how long-term experimental warming coupled with increased snow depth influence the trajectories of soil fungal communities in different tundra types. We compared edaphic variables and fungal community composition in experimental plots simulating the expected increase in summer warming and winter snow depth, based on DNA metabarcoding data. Fungal communities in the sampled dry and moist acidic tundra communities differed greatly, with tundra type explaining ca. one-third of compositional variation. Furthermore, dry and moist tundra appear to have different trajectories in response to climate change. Specifically, while both warming and increased snow depth had significant effects on fungal community composition and edaphic variables in dry tundra, the effect of increased snow was greater. However, in moist tundra, fungal communities mainly were affected by summer warming, while increased snow depth had a smaller effect and only on some functional groups. In dry tundra, microorganisms generally are limited by moisture in the summer and extremely low temperatures in winter, which is in agreement with the stronger effect of increased snow depth relative to warming. On the contrary, moist tundra soils generally are saturated with water, remain cold year-round and show relatively small seasonal fluctuations in temperature. The greater observed effect of warming on fungi in moist tundra may be explained by the narrower temperature optimum compared to those in dry tundra.

Daily and annual shell growth in a long-lived freshwater bivalve as a proxy for winter snowpack

To assess the potential of long-lived freshwater bivalve shells as a proxy for river environments, we examined daily and annual growth increments and analysed trace elements in the shells of Margaritifera laevis collected alive from the Shiribetsu River, located in the central western region of Hokkaido, Japan. The sum of the daily growth lines within a single annual increment corresponded to the days when the average daily water temperature was greater than 9 °C, suggesting that shell deposition occurred from spring to autumn. The growing degree days (GDD) are correlated with the maximum snow depth in winter and the average river discharge in spring. We conducted trace element microanalysis across daily and annual growth increments by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and compared the results with in situ environmental data. Sharp peaks in the barium/calcium ratio (Ba/Ca) observed during spring river discharge also suggest that the growth of Margaritifera shells is influenced by winter snow volume and meltwater. A 67-year profile of the standard growth index (SGI) estimated from twelve individual annual growth histories correlates to the annual snowfall accumulation. Distinct decadal variability is observed in the SGI and synchronized with the North Pacific Index and Pacific Decadal Oscillation. Sclerochronological approaches using Margaritifera shells could be valuable for reconstructing river and atmospheric conditions during the winter season, which is influenced by the Asian winter monsoon in the central Hokkaido region.

Ratio of isotopic parameters δ2H-δ18o in Late Pleistocene and Holocene ice wedge

The subject of this research is the ratio of isotopic parameters of deuterium of heavy oxygen in ice wedges. The authors considered such parameter as inclination of the line of the ration of deuterium of heavy oxygen in ice wedges. Proximal to GMLV (or LLMV) position of isotope values for ice wedge and inclination of the line proximate to 8 suggests that the ice wedge was formed from atmospheric precipitation (winter snow). The article provides separate examples of anomalous deuterium ratios of heavy oxygen with very low ration of line inclination, which in combination with the abnormally low dexc values indicate the indicate isotopic fractionation processes in snow before melting and/or melting snow water before filling frost-cutting cracks. Three author determines the three main types of ratios of deuterium m of heavy oxygen content in ice wedge: a) normal ratio δ2H-δ18O (with line inclination of the ratio proximate to GLMV or LLMW). b) ratio of deuterium  of heavy oxygen to deviation from GLMV or LLMW (with signs of change in the primary isotope signal of atmospheric precipitation), c) anomalous ratio of deuterium of heavy oxygen. It is shown that the first two types  are characteristic to most ice wedge under study in the vast part of the Russian cryolithozone from the European North to the east of Chukotka; the third type is obtained for several Holocene ice wedge in Transbaikal and upper Yenisei River. This may be explained by significant isotope transformation of snow cover in the conditions of distinctly continental climate.

Flowering Phenology Adjustment and Flower Longevity in a South American Alpine Species.

Delayed flowering due to later snowmelt and colder temperatures at higher elevations in the alpine are expected to lead to flowering phenological adjustment to prevent decoupling of peak flowering from the warmest time of the year, thereby favoring pollination. However, even if flowering is brought forward in the season at higher elevations, an elevational temperature gap is likely to remain between the high- and low-elevation populations of a species at the time these reach peak flowering on account of the atmospheric reduction in temperature with increasing elevation. The negative effect of this temperature gap on pollination could be compensated by plastically-prolonged flower life spans at higher elevations, increasing the probability of pollination. In a tightly temperature-controlled study, the flowering phenology adjustment and flower longevity compensation hypotheses were investigated in an alpine species in the Andes of central Chile. The snow free period varied from 7 to 8.2 months over 810 m elevation. Temperatures were suitable for growth on 82–98% of the snow free days. Flowering onset was temporally displaced at the rate of 4.6 d per 100 m increase in elevation and flowering was more synchronous at higher elevations. Flowering phenology was adjusted over elevation. The latter was manifest in thermal sums tending to decrease with elevation for population flowering onset, 50% flowering, and peak flowering when the lower thermal limit for growth (TBASE) was held constant over elevation. For TBASE graded over elevation so as to reflect the growing season temperature decline, thermal sums did not vary with elevation, opening the door to a possible elevational decline in the thermal temperature threshold for growth. Potential flower longevity was reduced by passive warming and was more prolonged in natural populations when temperatures were lower, indicating a plastic trait. Pollination rates, as evaluated with the Relative Pollination Rate index (RPR), when weighted for differences in floral abundance over the flowering season, declined with elevation as did fruit set. Contrary to expectation, the life-spans of flowers at higher elevations were not more prolonged and failed to compensate for the elevational decrease in pollination rates. Although strong evidence for phenological adjustment was forthcoming, flower longevity compensation did not occur over Oxalis squamata’s elevational range. Thus, flower longevity compensation is not applicable in all alpine species. Comparison with work conducted several decades ago on the same species in the same area provides valuable clues regarding the effects of climate change on flowering phenology and fitness in the central Chilean alpine where temperatures have been increasing and winter snow accumulation has been declining.

Recent Increases in Winter Snowfall Provide Resilience to Very Small Glaciers in the Julian Alps, Europe

Very small glaciers (<0.5 km2) account for more than 80% of the total number of glaciers and more than 15% of the total glacier area in the European Alps. This study seeks to better understand the impact of extreme snowfall events on the resilience of very small glaciers and ice patches in the southeastern European Alps, an area with the highest mean annual precipitation in the entire Alpine chain. Mean annual precipitation here is up to 3300 mm water equivalent, and the winter snow accumulation is approximately 6.80 m at 1800 m asl averaged over the period 1979–2018. As a consequence, very small glaciers and ice/firn patches are still present in this area at rather low altitudes (1830–2340 m). We performed repeated geodetic mass balance measurements on 14 ice bodies during the period 2006–2018 and the results show an increase greater than 10% increase in ice volume over this period. This is in accordance with several extreme winter snow accumulations in the 2000s, promoting a positive mass balance in the following years. The long-term evolution of these very small glaciers and ice bodies matches well with changes in mean temperature of the ablation season linked to variability of Atlantic Multidecadal Oscillation. Nevertheless, the recent behaviour of such residual ice masses in this area where orographic precipitation represents an important component of weather amplification is somehow different to most of the Alps. We analysed synoptic meteorological conditions leading to the exceptional snowy winters in the 2000s, which appear to be related to the influence and modification of atmospheric planetary waves and Arctic Amplification, with further positive feedbacks due to change in local sea surface temperature and its interactions with low level flows and the orography. Although further summer warming is expected in the next decades, we conclude that modification of storm tracks and more frequent occurrence of extreme snowfall events during winter are crucial in ensuring the resilience of small glacial remnants in maritime alpine sectors.

Too hot for our own good

Ice Sheets Climate is warming faster in the Arctic than in any other large region, and the Greenland Ice Sheet is melting faster as a result. Noel et al. project that the rate of summertime surface melting will surpass that of winter snow accumulation in Greenland when the average air temperature there rises to 4.5°C above preindustrial values, which corresponds to a global warming threshold of 2.7°C. Without strong CO2 emission mitigation measures, net surface mass loss could occur as soon as the middle of the 21st century. Geophys. Res. Lett. 10.1029/2020GL090471 (2021).

Compensation effect of winter snow on larch growth in Northeast China

Winter snow plays a crucial role in regulating tree growth during the subsequent growing season in regions suffering seasonal or even annual drought stress, but the mechanisms of the potential compensation effect of winter snow on subsequent growing-season tree growth are not well understood. In this study, we establish tree-ring chronologies of six larch forest stands along a marked drought gradient across Northeast China. We identify the spatial pattern in the compensation effects of winter snow on subsequent growing-season tree radial growth and uncover a potentially enhanced compensation effect in drier climates. Our results indicate that in snow-rich sites, winter snow tends to exert a significantly positive effect on tree growth during the growing season, whereas this growth compensation effect is reduced in drier sites. More importantly, our findings identify a much higher compensation effect of winter snow on growing-season larch growth in drier years (24.4–48.0%) than in wetter years (6.1–8.1%) at snow-rich sites. Given the projected increase in both severity and duration of droughts in temperate regions, the potential compensation effect of winter snow could play a crucial role in mediating the adaptation ability of boreal/hemi-boreal forest ecosystems in response to a warmer and drier future climate in these regions.

Ecosystem Processes Show Uniform Sensitivity to Winter Soil Temperature Change Across a Gradient from Central to Cold Marginal Stands of a Major Temperate Forest Tree

The magnitude and frequency of soil frost events might increase in northern temperate regions in response to climate warming due to reduced insulation caused by declining snow cover. In temperate deciduous forests, increased soil frost severity can hamper tree growth and increase the mortality of fine roots, soil fauna and microorganisms, thus altering carbon and nutrient cycling. From single-site studies, however, it is unclear how the sensitivities of these responses change along continental gradients from regions with low to high snowfall. We conducted a gradient design snow cover and soil temperature manipulation experiment across a range of lowland beech forest sites to assess the site-specific sensitivity of tree growth and biogeochemical cycling to soil cooling. Even mild and inconsistent soil frost affected tree increment, germination, litter decomposition and the retention of added 15N. However, the sensitivity of response (treatment effect size per degree of warming or cooling) was not related to prevailing winter climate and snow cover conditions. Our results support that it may be valid to scale these responses to simulated winter climate change up from local studies to regional scales. This upscaling, however, needs to account for the fact that cold regions with historically high snowfall may experience increasingly harsh soil frost conditions, whereas in warmer regions with historically low snowfall, soil frost may diminish. Thus, despite the uniform biotic sensitivity of response, there may be opposing directions of winter climate change effects on temperate forests along continental temperature gradients due to different trends of winter soil temperature.