Increased Snow Cover Research Articles

Increased Extreme Precipitation in May over Southwestern Xinjiang in Relation to Eurasian Snow Cover in Recent Years

Abstract In this study, the interdecadal variations of extreme precipitation in May over southwestern Xinjiang (SWX) and related mechanisms were investigated. The extreme precipitation in May over SWX exhibited a decadal shift in the 1990s (negative phase during 1970–86 and positive phase during 2003–18). The decadal shift corresponded to strengthened moist airflow from the Indian Ocean and an anomalous cyclone over SWX during 2003–18. It is found that the interdecadal change of the wave trains in Eurasia might account for the differences in atmospheric circulation between the above two periods. Further analyses reveal that spring snow cover over Eurasia is closely linked to extreme precipitation over SWX during 2003–18. Increased snow cover in western Europe (WE) from February to March is accompanied by more snowmelt. This resulted in less local snow cover and lower albedo, leading to warm temperatures over WE in May. The changes in temperatures increase the local 1000–500-hPa thickness over WE. These factors provide favorable conditions for the enhancement of the Eurasian wave trains, which significantly influence extreme precipitation over SWX. On the other hand, corresponding to decreased albedo caused by the reduction of snow cover in northern Eurasia (NE) in May, anomalous surface warming occurs over NE. The anomalous warming results in positive geopotential height anomalies that intensify the meridional geopotential height gradient over Eurasia and cause an acceleration of the westerly jet in May. Anomalous upper-level divergence in SWX induced by the enhanced westerly jet provides a favorable dynamical condition for increased extreme precipitation.

Spatio-temporal dynamics in microalgal communities in Arctic land-fast sea ice

Sea ice microalgae are an important source of energy for the polar marine food web, representing the primary carbon source prior to pelagic phytoplankton blooms. Here we investigate community dynamics of sea ice microalgal communities in land-fast sea ice across six different fjords in high-Arctic Svalbard, Norway, during Spring (April – May). We found that light (0.1 – 23% incoming PAR / 0.1 – 193 μmol photons m-2s-1) played a central role in determining community composition, with more diverse assemblages observed in sites with more light transmitted to the bottom ice community. In April, microalgal assemblages were similar when under-ice light transmittance was similar, independent of geographical location, however this light-derived separation of community structure was not evident in May. At all sites, assemblages were dominated by pennate diatoms, with the most abundant taxon being Nitzschia frigida. However, with increasing under-ice light transmittance, we saw an increase in the relative abundance of Dinophyceae, Navicula spp. and Thalassiosira spp.. A positive relationship between light and δ13C enrichment and C:N ratios in the ice algal biomass demonstrated the effect of light on the biochemical composition of ice algae. Light did not correlate with cell abundance or chlorophyll a concentration. With anticipated changes to Arctic sea ice extent and snow cover as a result of climate change, we will see shifts in the light transmitted to the bottom ice community. These shifts, whether caused by reduced light transmittance from increased snow cover or increased light transmittance from thinning ice, snow depth or increased rainfall, will likely alter sea ice microalgal community composition, which in turn, may influence the success of secondary production and biogeochemical cycling in polar waters.

Quantitative Changes in the Surface Frozen Days and Potential Driving Factors in Northern Northeastern China

Surface freezing and thawing processes pose significant influences on surface water and energy balances, which, in turn, affect vegetation growth, soil moisture, carbon cycling, and terrestrial ecosystems. At present, the changes in surface freezing and thawing states are hotspots of ecological research, but the variations of surface frozen days (SFDs) are less studied, especially in the permafrost areas covered with boreal forest, and the influence of the environmental factors on the SFDs is not clear. Utilizing the Advanced Microwave Scanning Radiometer for EOS (AMSRE) and Microwave Scanning Radiometer 2 (AMSR2) brightness temperature data, this study applies the Freeze–Thaw Discriminant Function Algorithm (DFA) to explore the spatiotemporal variability features of SFDs in the Northeast China Permafrost Zone (NCPZ) and the relationship between the permafrost distribution and the spatial variability characteristics of SFDs; additionally, the Optimal Parameters-based Geographical Detector is employed to determine the factors that affect SFDs. The results showed that the SFDs in the NCPZ decreased with a rate of −0.43 d/a from 2002 to 2021 and significantly decreased on the eastern and western slopes of the Greater Khingan Mountains. Meanwhile, the degree of spatial fluctuation of SFDs increased gradually with a decreasing continuity of permafrost. Snow cover and air temperature were the two most important factors influencing SFD variability in the NCPZ, accounting for 83.9% and 74.8% of the spatial variation, respectively, and SFDs increased gradually with increasing snow cover and decreasing air temperature. The strongest explanatory power of SFD spatial variability was found to be the combination of air temperature and precipitation, which had a coefficient of 94.2%. Moreover, the combination of any two environmental factors increased this power. The findings of this study can be used to design ecological environmental conservation and engineer construction policies in high-latitude permafrost zones with forest cover.

Investigating sources of variability in closing the terrestrial water balance with remote sensing

Abstract. Remote sensing (RS) data are becoming an increasingly important source of information for water resource management as they provide spatially distributed data on water availability and use. However, in order to guide appropriate use of the data, it is important to understand the impact of the uncertainties of RS data on water resource studies. Previous studies have shown that the degree of closure of the water balance from remote sensing data is highly variable across basins and that different RS products vary in their levels of accuracy depending on climatological and geographical conditions. In this paper, we analyzed the water-balance-derived runoff from global RS products for 931 catchments across the globe. We compared time series of runoff estimated through a simplified water balance equation using three precipitation (CHIRPS, GPM, and TRMM), five evapotranspiration (MODIS, SSEBop, GLEAM, CMRSET, and SEBS), and three water storage change (GRACE-CSR, GRACE-JPL, and GRACE-GFZ) RS datasets with monthly in situ discharge data for the period 2003–2016. Results were analyzed through the lens of 10 quantifiable catchment characteristics in order to investigate correlations between catchment characteristics and the quality of RS-based water balance estimates of runoff and whether specific products performed better than others under certain conditions. The median Nash–Sutcliffe efficiency (NSE) for all gauges and all product combinations was −0.02, and only 44.9 % of the time series reached a positive NSE. A positive NSE could be obtained for 73.7 % of stations with at least one product combination, while the overall best-performing product combination was positive for 58.4 % of stations. This confirms previous findings that the best-performing products cannot be globally established. When investigating the results by catchment characteristic, all combinations tended to show similar correlations between catchment characteristics and the quality of estimated runoff, with the exception of combinations using MODIS evapotranspiration, for which the correlation was frequently reversed. The combinations with the GPM precipitation product generally performed worse than the CHIRPS and TRMM data. However, this can be attributed to the fact that the GPM data are available at higher latitudes compared to the other products, where performance is generally poorer. When removing high-latitude stations, this difference was eliminated, and GPM and TRMM showed similar performance. The results show the highest positive correlation between highly seasonal rainfall and runoff NSE. On the other hand, increasing snow cover, altitude, and latitude decreased the ability of the RS products to close the water balance. The catchment's dominant climate zone was also found to be correlated with time series performance, with the tropical areas providing the highest (median NSE = 0.11) and arid areas the lowest (median NSE = −0.09) NSE values. No correlation was found between catchment area and runoff NSE. The results highlight the importance of further studies on the uncertainties of the different data products and how these interact when combining them, as well as of new approaches to using the data rather than simple water-balance-type approaches. Efforts to improve specific satellite products can also be better targeted using the results of this study.

Moss kill dates and modeled summer temperature track episodic snowline lowering and ice cap expansion in Arctic Canada through the Common Era

Abstract. Most extant ice caps mantling low-relief Arctic Canada landscapes remained cold based throughout the late Holocene, preserving in situ bryophytes killed as ice expanded across vegetated landscapes. After reaching peak late Holocene dimensions ∼1900 CE, ice caps receded as Arctic summers warmed, exposing entombed vegetation. The calibrated radiocarbon ages of entombed moss collected near ice cap margins (kill dates) define when ice advanced across the site, killing the moss, and remained over the site until the year of their collection. In an earlier study, we reported 94 last millennium radiocarbon dates on in situ dead moss collected at ice cap margins across Baffin Island, Arctic Canada. Tight clustering of those ages indicated an abrupt onset of the Little Ice Age at ∼1240 CE and further expansion at ∼1480 CE coincident with episodes of major explosive volcanism. Here we test the confidence in kill dates as reliable predictors of expanding ice caps by resampling two previously densely sampled ice complexes ∼15 years later after ∼250 m of ice recession. The probability density functions (PDFs) of the more recent series of ages match PDFs of the earlier series but with a larger fraction of early Common Era ages. Post 2005 CE ice recession has exposed relict ice caps that grew during earlier Common Era advances and were preserved beneath later ice cap growth. We compare the 106 kill dates from the two ice complexes with 80 kill dates from 62 other ice caps within 250 km of the two densely sampled ice complexes. The PDFs of kill dates from the 62 other ice caps cluster in the same time windows as those from the two ice complexes alone, with the PDF of all 186 kill dates documenting episodes of widespread ice expansion restricted almost exclusively to 250–450 CE, 850–1000 CE, and a dense early Little Ice Age cluster with peaks at ∼1240 and ∼1480 CE. Ice continued to expand after 1480 CE, reaching maximum dimensions at ∼1880 CE that are still visible as zones of sparse vegetation cover in remotely sensed imagery. Intervals of widespread ice cap expansion coincide with persistent decreases in mean summer surface air temperature for the region in a Community Earth System Model (CESM) fully coupled Common Era simulation, suggesting the primary forcings of the observed snowline lowering were both modest declines in summer insolation and cooling resulting from explosive volcanism, most likely intensified by positive feedbacks from increased snow cover and sea ice and reduced northward heat transport by the oceans. The clusters of ice cap expansion defined by moss kill dates are mirrored in an annually resolved Common Era record of ice cap dimensions in Iceland, suggesting this is a circum-North-Atlantic–Arctic climate signal for the Common Era. During the coldest century of the Common Era, 1780–1880 CE, ice caps mantled >11 000 km2 of north-central Baffin Island, whereas <100 km2 is glaciated at present. The peak Little Ice Age state approached conditions expected during the inception phase of an ice age and was only reversed after 1880 CE by anthropogenic alterations of the planetary energy balance.

Increased Persistence in Winter-to-Spring Precipitation Anomalies over South China since the Late 1990s and the Possible Mechanisms

Abstract This study reveals that South China precipitation (SCP) anomalies tend to persist well from winter to the following spring after the late 1990s, favoring long-lasting drought or flood events over South China. Mechanism analysis indicates that the interdecadal changes in El Niño–Southern Oscillation (ENSO) and the preceding November central Asian snow cover could contribute to the increased persistence of winter-to-spring SCP anomalies. ENSO has a stable impact on winter SCP, whereas its impact on spring SCP is significantly enhanced after the late 1990s. With a weakened intensity and faster decay rate in the recent two decades, the ENSO-related spring SST anomalies over the tropical Pacific are relatively weaker, inducing a weakened and more southward-located western North Pacific anticyclone. This further leads to an interdecadal migration of the spring rainfall belt anomaly, consequently favoring the persistence of winter-to-spring SCP anomalies after the late 1990s. Additionally, the impacts of November central Asian snow cover on winter and spring SCP are both strengthened after the late 1990s. In the most recent two decades, the snow-cover-related cooling effect has become stronger, which induces winter cyclonic anomalies over Lake Baikal, favoring increased winter SCP. In addition, increased snow cover excites upward-propagating waves from the troposphere to the stratosphere, consequently weakening the stratospheric polar vortex. In spring, the stratospheric polar vortex signals propagate downward and result in a negative Arctic Oscillation in the troposphere, favoring more spring SCP. Therefore, central Asian snow cover is also conductive to the persistence of winter-to-spring SCP anomalies after the late 1990s.

A landscape-level study on vegetation richness of ancient landslide areas

Landslides have received significant attention as an important natural disturbance that maintains biodiversity, but most previous studies have focused on the early stages of succession during years or decades in sites or small watersheds. The present study aimed to determine what regional drivers influence long-term ecological succession in large, ancient landslide scarps across a mountainous region in Japan. A landscape-level analysis of 993 landslide scarps using GIS revealed that climatic factors, especially snowfall, are important regional drivers of vegetation development on landslide head scarps in the region. While vegetation has developed on ancient landslide scarps, not all of them have returned to their pre-landslide vegetation state even though hundreds or thousands of years may have passed. The relationship between the number of vegetation types and maximum snow depth shows that where the maximum snow depth is less than 100 cm, more than 50% of the landslide scarps are covered by one type of vegetation, and the percentage of scarps covered by one type of vegetation decreases with increasing snow cover. The deeper the snow, the more vegetation types tend to develop on the landslide scarps. Since forest vegetation cannot develop due to heavy snow, meadows, grasslands, and shrublands are found on the scarps. It is concluded that the combined effects of both landslide-caused disturbances and climatic factors are creating regional diversity in vegetation types.

The impact of climate change on seasonal glaciation in the mountainous permafrost of North-Eastern Eurasia by the example of the giant Anmangynda aufeis

This study examines the evolving dynamics of spring aufeis fields in the mountain permafrost zone of North-Eastern Eurasia, emphasizing their significance as indicators of permafrost-hydrogeological processes. Focusing on the representative Anmangynda river basin giant aufeis field, our research spans 1962 to 2022 and unveils temporal variations in aufeis characteristics.Over the historical period (1963–1990), the aufeis maximum pre-ablation area ranged from 4.3 to 6.8 km2, with a volume of 5.3 to 11.7 million m3. In the present era (2000–2022), these figures decreased to 3.5–5.4 km2 and 5.0–8.2 million m3, respectively. The region experienced heightened air temperatures and precipitation, with the most significant shifts occurring during early winter (October–December). Increased snow cover depth and earlier formation were also observed. Ground temperatures followed suit with an upward trend. Correlation analyses reveal a noteworthy link between average air temperatures from August to November and aufeis characteristics in both historical and current contexts. Moreover, solid precipitation and air temperatures in November and December displayed a moderate yet statistically significant correlation with aufeis size parameters during 2000–2022. Notably, no significant correlation emerged between aufeis characteristics and the Anmangynda River streamflow or liquid precipitation. This research underscores the interplay between climatic variables and aufeis dynamics, offering insights into the impacts of changing climatic conditions on the permafrost-hydrogeological system. The observed reduction of aufeis area and volume, coupled with the altered freezing and melting periods, align with broader cryospheric changes. As aufeis fields continue to evolve, this study highlights the complexities in their responses and their relevance as indicators of climate-driven alterations in the cryosphere. Further research is essential to fully unravel these intricate relationships and assess their implications for regional hydrology and ecosystems.

Increased snow cover enhances gross primary productivity in cold and dry regions of the Tibetan Plateau

AbstractSnow cover is an important control element in the Tibetan Plateau (TP) ecosystem; however, the impact of snow cover changes on gross primary productivity (GPP) is largely unknown, particularly under complex geographical conditions. In this study, we investigated the impacts of snow cover changes on different seasonal GPP and their mechanisms in different geographical zones using multisource remote sensing data from 1982 to 2018. Snow cover significantly affected GPP by nearly 15% of the TP region, and snow cover days (SCDs) were the dominant snow cover indicators affecting GPP variations compared with snow water equivalent (SWE) and snow cover end date (SCED). In general, an increase in snow cover leads to a significant increase in GPP in regions with low precipitation and temperature, but limits the accumulation of GPP in humid and warm regions. Furthermore, from the humid to the arid zone, the “moisture effect” of snow cover (by altering soil moisture) plays an increasingly important role in regulating GPP variations with increasing drought levels. This study elucidates the importance of snow cover in regulating different seasonal GPP variations and significantly improves our insight into the response of vegetation carbon uptake to snow cover changes in the TP.

Impact of ENSO on Wintertime Land Surface Variables in Northern Hemisphere Extratropics: Role of Atmospheric Moisture Processes

Abstract El Niño–Southern Oscillation (ENSO) is the strongest interannual signature in the tropical air–sea system and can affect global atmospheric variables, but ENSO’s climatic impact on land surface variables such as skin temperature, snow cover, and soil moisture that can serve as seasonal climate predictors remains relatively little known. Here we examine ENSO’s impact on the three land surface variables in Northern Hemisphere extratropics by regression analysis, using a combination of ERA5 reanalysis, GLDAS, satellite-based observations, and CESM2 simulations. Our results show that during El Niño winters anomalous land surface warming occurs in Northern Hemisphere midlatitudes, accompanied by snow cover reduction, especially in northern North America and eastern Europe, while anomalous cooling occurs in southern North America and the Tibetan Plateau, accompanied by increased snow cover. Meanwhile, increased soil moisture is observed in southern North America, central Asia, and southeast China. Further analysis indicates that atmospheric moisture processes dominate the formation of the land surface anomalies, for which the changes in water vapor and precipitation induced by the ENSO-related large-scale atmospheric teleconnection are critical. The anomalous land surface warming in midlatitudes mainly results from the increased downward longwave radiation due to the increase of water vapor, whereas the physical pathway causing water vapor anomalies is different over North America and Eurasia. Controlled by ENSO-induced changes in atmospheric circulation and moisture transport, anomalous precipitation explains most of the snow cover and soil moisture anomalies, which play a certain role in shaping the skin temperature anomalies in some regions through snow–albedo feedback and evaporation, respectively.

Plants alter their aboveground and belowground biomass allocation and affect community-level resistance in response to snow cover change in Central Asia, Northwest China

It is important to elucidate the changing distribution pattern of net primary productivity (NPP) to mechanistically understand the changes in aboveground and belowground ecosystem functions. In water-scarce desert environments, snow provides a crucial supply of water for plant development and the spread of herbaceous species. Yet uncertainty persists regarding how herbaceous plants' NPP allocation responds to variation in snow cover. The goal of this study was to investigate how variation in snow cover in a temperate desert influenced the NPP allocation dynamics of herbaceous species and their resistance to environmental change in terms aboveground and belowground productivity. In the Gurbantunggut Desert, wintertime snow cover depth was adjusted in plots by applying four treatments: snow removal (−S), ambient snow, double snow (+S), and triple snow (+2S). We examined their species richness, aboveground NPP (ANPP), belowground NPP (BNPP), and the resistance of ANPP and BNPP. We found that species diversity of the aboveground community increased significantly with increasing snow cover and decreased significantly Pielou evenness in plots. This resulted in greater ANPP with increasing snow cover; meanwhile, BNPP first increased and then decreased with increasing snow cover. However, this productivity in different soil layers responded differently to changed snow cover. In the 0–10 cm soil layer, productivity first rose and then declined, while it declined linearly in both the 10–20 cm and 20–30 cm soil layers, whereas in the 30–40 cm soil layer it showed an increasing trend. Belowground resistance would increase given that greater snow cover improved the BNPP in deeper soil and maintained the resource provisioning for plant growth, thus improving overall belowground stability. These results can serve as a promising research foundation for future work on how the functioning of desert ecosystems becomes altered due to changes in plant community expansion and, in particular, changes in snow cover driven by global climate change.

Effects of Snow Cover on Carbon Dioxide Emissions and Their δ13C Values of Temperate Forest Soils with and without Litter

The presence of litter and winter snow cover can affect the decomposition of organic matter in forest soils and changes in δ13C values of soil-respired carbon dioxide (CO2). However, limited information is available on the responses of CO2 emissions from forest soils and their δ13C values to snow cover and litter addition over the year. We experimentally manipulated snow cover to study the impacts of light and heavy artificial snow cover on soil heterotrophic respiration and its δ13C values, using undisturbed large soil columns collected from two typical temperate forests in Northeastern China. Based on the average temperatures of surface forest soils in four seasons of the year in this study region, the simulations of autumn freeze–thaw, winter freeze, spring freeze–thaw, and the growing season were sequentially carried out under laboratory conditions. A set of novel analysis systems, including automated chamber equipment and laser spectroscopy analysis with high-frequency measurements for CO2 concentrations and the 13C/12C isotopic ratios in CO2, was used to study the effects of artificial snow cover and the presence of litter on soil heterotrophic respiration and its δ13C values. During the autumn freeze–thaw simulation, there were larger CO2 emissions and less negative δ13C values of soil-respired CO2 upon heavy snow cover than upon light snow cover, indicating that the presence of increased snow cover prior to winter freeze can increase the decomposition of organic C in subsurface soils under temperate forests. The δ13C values of soil-respired CO2 in all treatments were, on average, less negative as the simulated spring freeze–thaw proceeded, which was contrary to the variations of the δ13C during the autumn freeze–thaw simulation. Soil heterotrophic respiration and its δ13C values during the spring freeze–thaw simulation were, on average smaller upon heavy snow cover than upon light snow cover, which differed from those during the autumn freeze–thaw and growing season simulations, respectively. Taken together, the results highlight that the effects of snow cover on soil heterotrophic respiration and its δ13C values under temperate forests may vary with different seasons of the year and the presence of litter.

Stimulating effects of snow cover on gaseous nitrogen emissions are intensified by biological soil crusts

Winter weather patterns are changing due to global climate change, which impacts the soil nitrogen cycle and greenhouse gas flux in these ecosystems, particularly the snow cover in temperate deserts. Biological soil crusts are important soil communities of the desert ecosystem and are sensitive to environmental changes. However, knowledge of the responses of gaseous nitrogen emissions from biological soil crusts to changes in snow cover is limited. In this study, the effects of snow cover on gaseous nitrogen emissions and the abundance of nitrifier (amoA) and denitrifier (narG, nirS, nirK, nosZ) genes were investigated in three snow cover treatments (snow removal, ambient snow, and increased snow depth). Snow cover significantly affected N2O and NO emissions from bare sand and biological soil crusts in winter. The abundance of denitrifier genes in bare sand and biological soil crusts and the abundance of nitrifier genes in moss crust increased with the depths of snow addition. N2O emissions increased with the successional stages of biological soil crusts during the winter. Both N2O and NO emissions from bare sand and biological soil crusts peaked in the freeze–thaw period (March) and were lowest in mid-winter (January). The emissions of N2O increased with increasing the abundance of amoA, nirK and nosZ genes. Our findings show that N2O emissions generally increased with increasing snow cover through their effects on nitrogen cycle related functional microbial groups. These effects were regulated by the types of biological soil crust, which can increase the effect of snow cover in winter.

The impact of climate change on monthly baseflow trends across Canada

Baseflow, the groundwater contribution to streamflow, sustains surface water between precipitation events and is an important indicator of groundwater availability. Although many site-specific studies have been completed, there are few studies of long-term Canada-wide baseflow trends. In this work, we detected monthly baseflow trends across Canada and related them to changes to climatic predictors (precipitation, temperature, and antecedent wetness) using streamflow data from 1275 hydrometer stations from 1989 to 2019. Lyne and Hollick’s one-parameter digital filter is used to obtain a baseflow time series and monotonic trends are identified using the Mann-Kendall Trend Test. Historical baseflow is related to climate parameters by means of Generalised Additive Models for Location, Scale and Shape (GAMLSS) statistical analysis. Results based on trend analysis detected no significant trends for most stations (85.7% of all stations and months). However, notable increasing trends were observed across most of southern Canada during the winter and spring months (October–April). Conversely, negative trends were detected from June to September in Alberta and British Columbia and in southern Northwest Territories. Model selection identified antecedent wetness most often as a climate predictor over the same period as trend analysis. Our results highlight that warmer temperatures and increased snow cover across much of Canada have contributed to increased baseflow likely from shifts in snow melt timing and volumes. During warmer months (June–August), results indicate that increases in temperature were related to decreased baseflow, likely through increased evapotranspiration. Many trends in baseflow were not related to any climate predictors. Furthermore, non-reference basins were twice as likely to have no climate predictor, indicating that anthropogenic activities may be driving changes in baseflow. The results of this work can inform water resources management to identify the direction of change in groundwater availability across Canada and regions where mitigation may be necessary.

Contrasting changes of snow cover between different regions of the Tibetan Plateau during the latest 21 years

The spatial and temporal resolutions of snow remote sensing data have been increasing, but the unique snow characteristics such as thin snow depth and high frequency of change on the Tibetan Plateau have limited their applicability in this region. In this study, five commonly used snow remote sensing data were evaluated based on snow observations at 139 stations during the latest 20 years, and the advantages of each data were integrated to develop a multi-source data fusion snow cover dataset for the Tibetan Plateau. Based on these data, we conducted snow zonation and comparative snow variability analysis on the Tibetan Plateau. The results indicated that the snow cover days on the Tibetan Plateau are not only influenced by the longest snow cover duration (SCD) but also controlled by the short-term snow cycles. More than 70% of the annual snow cover days come from short-term snow cycles, except the Amu Darya and Indus. From 2000 to 2021, 23.0% of the plateau has experienced a significant decrease in snow cover days (mainly in the southeast) and 4.9% has experienced a significant increase (mainly in the northwest). As the altitude increases, the area and magnitude of the decreased and increased snow cover increases, and at high altitude the areas with increased snow are greater than that with decreased. The significant reduction in the snow cover days over large areas of the plateau stems from the superimposed effect of the simultaneous reductions in the longest SCD and the short-term snow cycles, but the reduction in the Amu Darya and Indus comes mainly from the reduction in the short-term snow cycle. The significant increase in the snow cover days in the Amu Darya, Indus, Tarim, and Hexi mainly comes from the increase in the longest SCD, while that in the Yellow River and Qaidam mainly comes from the increase in the short-term snow cycles. This contrasting change in the snowpack on the Tibetan Plateau, which decreases in the southeast and increases in the northwest, with a large decrease at lower elevations and an increase at higher elevations, will bring new challenges to water resource management in the region.

Tularemia above the Treeline: Climate and Rodent Abundance Influences Exposure of a Sentinel Species, the Arctic Fox (Vulpes lagopus), to Francisella tularensis

Tularemia is a zoonotic disease found throughout most of the northern hemisphere that may experience range expansion with warming temperatures. Rodents and lagomorphs are reservoirs for the disease, and outbreaks of tularemia often follow peaks in their abundance. As small mammals dominate the diet of arctic foxes (Vulpes lagopus), we determined whether they may serve as sentinels by identifying antibodies in live-captured and harvested foxes from northern Canada. Overall seroprevalence was 2% (CI95 1-2%) in 176 foxes harvested in 2018-2019 compared to 17% (CI95 12-22%) of 230 foxes captured live in 2011-2021. Prevalence was at an all-time high in 2018, following a peak in vole abundance in 2017. Antibodies were identified in fox pups born in 2018 and 2019, suggesting that F. tularensis was actively transmitted during the summers. High precipitation during the summer, increased snow cover and colder temperatures in May, and a higher abundance of voles were all associated with increased seroprevalence in live-captured foxes. Thus, exposure to F. tularensis is largely mediated through climate and rodent populations in the Canadian Arctic, and arctic foxes are useful sentinels for F. tularensis in northern ecosystems. Further studies should investigate whether infection impacts arctic fox survival and reproductive success in the circumpolar North.

A decade of cold Eurasian winters reconstructed for the early 19th century

Annual-to-decadal variability in northern midlatitude temperature is dominated by the cold season. However, climate field reconstructions are often based on tree rings that represent the growing season. Here we present cold-season (October-to-May average) temperature field reconstructions for the northern midlatitudes, 1701-1905, based on extensive phenological data (freezing and thawing dates of rivers, plant observations). Northern midlatitude land temperatures exceeded the variability range of the 18th and 19th centuries by the 1940s, to which recent warming has added another 1.5 °C. A sequences of cold winters 1808/9-1815/6 can be explained by two volcanic eruptions and unusual atmospheric flow. Weak southwesterlies over Western Europe in early winter caused low Eurasian temperatures, which persisted into spring even though the flow pattern did not. Twentieth century data and model simulations confirm this persistence and point to increased snow cover as a cause, consistent with sparse information on Eurasian snow in the early 19th century.

High‐Resolution Elemental Record From the Holocene Sediments of an Alpine Lake in the Central Altai Mountains: Implications for Arctic Sea‐Ice Variations

AbstractIt is well known that Arctic sea ice and Arctic amplification have played an important role in recent climate change in middle to high latitudes of the Northern Hemisphere. We present a high‐resolution elemental data set, spanning the past 9,000 years, obtained using in‐situ synchrotron radiation X‐ray fluorescence measurements of a lake sediment core from Lake Shuang in the Altai Mountains. Based on calibration against the local instrumental climatic record, the Rb/Sr ratio of the sediments is interpreted as an indicator of weathering intensity, which is related to precipitation and temperature variations. There is very little bromine in the granites and moyites in the catchment of Lake Shuang, and the sedimentary Br is derived primarily from wet deposition originating from precipitation and enriched by biogenic processes in this open lake system. The Br variation is positively correlated with local precipitation. The Rb/Sr and Br time series show distinct decadal‐scale to millennial‐scale cycles that are similar to those of Arctic sea‐ice variations, which implies the important role of Artic sea ice in modulating environmental change at Lake Shuang. Our results support a previous suggestion that sea ice loss would cause an increase in atmospheric water vapor content in the Arctic, resulting in the frequent incursion of cold air masses from the Arctic into middle latitudes, and leading to increased snow cover and precipitation, and vice versa.

How will snow retention and shading from Arctic shrub expansion affect caribou food resources?

ABSTRACT Increased snow cover and attenuation of light due to shrub expansion can lead to changes in the quantity and nutritional quality of food resources for migratory caribou (Rangifer tarandus). To determine how vegetation is affected by snow accumulation and shade, we conducted an experiment that simulated the light and snow conditions created by increased shrub cover at Deception Bay (Nunavik, Canada), within the summer range of the Rivière-aux-Feuilles caribou herd. We estimated the foliar biomass of two major components of the caribou diet (Betula glandulosa and Carex spp.). We also harvested foliar tissue to conduct chemical composition analyses (nitrogen, fibre, total phenolics). Experimental light attenuation was found to increase the nitrogen concentrations in B. glandulosa and Carex spp. throughout the growing season. Phenolic concentration in B. glandulosa decreased in early summer but was otherwise consistent in response to light attenuation and increased snow cover. Increased snow cover combined with ambient light had a positive effect on the foliar biomass of B. glandulosa. Increased snow cover and shade caused by shrub densification may therefore increase forage quantity and quality for caribou. We suggest investigating the effects of shrub expansion on other components of the caribou diet, such as lichens and forbs.

Intra‐specific variation in migration phenology of American Kestrels (Falco sparverius) in response to spring temperatures

In migratory birds, among‐ and within‐species heterogeneity in response to climate change may be attributed to differences in migration distance and environmental cues that affect timing of arrival at breeding grounds. We used eBird observations and a within‐species comparative approach to examine whether migration distance (with latitude as a proxy) and weather predictors can explain spring arrival dates at the breeding site in a raptor species with a widespread distribution and diverse migration strategies, the American Kestrel Falco sparverius. We found an interactive effect between latitude and spring minimum temperatures on arrival dates, whereby at lower latitudes (short‐distance migrants) American Kestrels arrived earlier in warmer springs and later in colder springs, but American Kestrels at higher latitudes (long‐distance migrants) showed no association between arrival time and spring temperatures. Increased snow cover delayed arrival at all latitudes. Our results support the hypothesis that short‐distance migrants are better able to respond to conditions on the breeding ground than are long‐distance migrants, suggesting that long‐distance migrants may be more vulnerable to shifts in spring conditions that could lead to phenological mismatch between peak resources and nesting.