Search Results (11)

In the past 42 years from 1980 to 2021, 103 regional strong cooling events (RSCEs) occurred in winter in Northeast China, and the frequency has increased significantly in the past 10 years, averaging 2.45 per year. The longest (shortest) duration is 10 (2) days. The minimum temperature series in 60 events exists in 10–20 d of significant low-frequency (LF) periods. The key LF circulation systems affecting RSCEs include the Lake Balkhash–Baikal ridge, the East Asian trough (EAT), the robust Siberian high (SH) and the weaker (stronger) East Asian temperate (subtropical) jet, with the related anomaly centers moving from northwest to southeast and developing into a nearly north–south orientation. The LF wave energy of the northern branch from the Atlantic Ocean disperses to Northeast China, which excites the downstream disturbance wave train. The corresponding LF positive vorticity enhances and moves eastward, leading to the formation of deep EAT. The enhanced subsidence motion behind the EAT leads to SH strengthening. The cold advection related to the northeast cold vortex is the main thermal factor causing the local temperature to decrease. The Scandinavian Peninsula is the primary cold air source, and the Laptev Sea is the secondary one, with cold air from the former along northwest path via the West Siberian Plain and Lake Baikal, and from the latter along the northern path via the Central Siberian Plateau, both converging towards Northeast China. Full article

Understanding how pollen assemblages represent the local and regional vegetation composition is crucial for palaeoecological research. Here, we analyze 102 surface moss/soil pollen samples collected from four study regions located in various boreal forest vegetation types in Central Siberia. Despite Larix being the most prevalent tree generus in the study area, the proportion of Larix pollen can be as low as 0.6–1.5% (0.4–4.7% on average) even in localities with a high canopy density of the species. No relationship between the quantity of Larix pollen in the spectra and the abundance of Larix in the local vegetation was found. The dominant components of the pollen assemblages are Betula and Alnus fruticosa. The pollen value of Picea is low (2.6–8.2% on average), with higher proportions at sample plots where spruce is abundant in forests. Pinus is a highly prevalent pollen species within its geographical range, comprising up to 40% of pollen assemblages. Outside of the range, the ratio of Pinus pollen was higher in habitats with low canopy density and in treeless ecosystems. The composition of herbaceous pollen and spores is significantly affected by the local plant community, offering more comprehensive insights into past vegetation patterns. Full article

The fire risks in the vast Eurasian Subarctic are increasing, raising concerns for both local and global climate systems. Although some studies have addressed this problem, their conclusions only draw from relatively lower resolution data, and the sub-regional analysis of fire patterns in this area is lacking. In this paper, using a huge amount of multi-temporal and multi-resolution remotely sensed data, derived products, and weather data between the period 2001 and 2021, we reveal several novel and recent findings concerning regional and overall fire patterns in the Eurasian Subarctic. First, we discovered that fire occurrence over the period 2001 and 2021 varied by sub-region within the Eurasian Subarctic, with perennial low fire incidence in the East European and West Siberian Plain, increasing fire incidence in the Central Siberian Plateau, and marked periodicity of fire in the East Siberian Highlands. Second, we reveal the larger scale of individual fires in the Eurasian Subarctic compared to the adjacent region to the south, with fires of longer duration (13 vs. 8 days), larger daily expansion area (7.5 vs. 3.0 km²/d), and faster propagation (442 vs. 280 m/d). Third, the northern limit of fire has extended poleward approximately 1.5° during the study period. Fourth, the start dates of fire seasons in Eurasian Subarctic, dominated by the Central Siberian Plateau, has advanced at a rate of 1.4 days per year. We also analyzed the factors resulting in the regional patterns of fire incidence including weather, human activity, land cover, and landscape structure. Our findings not only increase the knowledge of regional fire patterns and trends in Eurasian Subarctic but also will benefit the design of special fire management policies. Full article

Snow cover is an important part of the Earth’s surface and its changes affect local and even global climates due to the high albedo and heat insulation. However, it is difficult to directly compare the results of previous studies on changes in snow cover in the Northern Hemisphere mainland (NH) due to the use of different datasets, research methods, or study periods, and a lack comparison in terms of the differences and similarities at high latitudes and high altitudes. By using snow depth datasets, we analyzed the spatio-temporal distributions and variations in snow depth (SD) and snow phenology (SP) in the NH and nine typical areas. This study revealed that SD in the NH generally decreased significantly (p < 0.01) from 1988 to 2018, with a rate of −0.55 cm/decade. Changes in SD were insignificant at high altitudes, but significant decreases were found at high latitudes. With regard to SP, the snow cover onset day (SCOD) advanced in 31.57% of the NH and was delayed in 21.10% of the NH. In typical areas such as the Rocky Mountains, the West Siberian Plain, and the Central Siberian Plateau, the SCOD presented significant advancing trends, while a significant delay was the trend observed in the Eastern European Plain. The snow cover end day (SCED) advanced in 37.29% of the NH and was delayed in 14.77% of the NH. Negative SCED trends were found in most typical areas. The snow cover duration (SCD) and snow season length (SSL) showed significant positive trends in the Rocky Mountains, while significant negative trends were found in the Qinghai–Tibet Plateau. The results of this comprehensive comparison showed that most typical areas were characterized by decreased SD, advanced SCOD and SCED, and insignificantly increasing SCD and SSL trends. The SCD and SSL values were similar at high latitudes, while the SSL value was larger than the SCD value at high altitudes. The SD exhibited similar interannual fluctuation characteristics as the SCD and SSL in each typical area. The SCD and SSL increased (decreased) with advanced (delayed) SCODs. Full article

Climate change has led to shifts in species distribution and become a crucial factor in the extinction of species. Increasing average temperatures, temperature extremes, and unpredictable weather events have all become a part of a perfect storm that is threatening ecosystems. Higher altitude habitats are disproportionately affected by climate change, and habitats for already threatened specialist species are shrinking. The Siberian ibex, Capra sibirica, is distributed across Central Asia and Southern Siberia and is the dominant ungulate in the Pamir plateau. To understand how climate change could affect the habitat of Siberian ibex in the Taxkorgan Nature Reserve (TNR), an ensemble species distribution model was built using 109 occurrence points from a four-year field survey. Fifteen environmental variables were used to simulate suitable habitat distribution under different climate change scenarios. Our results demonstrated that a stable, suitable habitat for Siberian ibex was mostly distributed in the northwest and northeast of the TNR. We found that climate change will further reduce the area of suitable habitat for this species. In the scenarios of RCP2.6 to 2070 and RCP8.5 to 2050, habitat loss would exceed 30%. In addition, suitable habitats for Siberian ibex will shift to higher latitudes under climate change. As a result, timely prediction of the distribution of endangered animals is conducive to the conservation of the biodiversity of mountain ecosystems, particularly in arid areas. Full article

The occurrence of droughts has become more frequent, and their intensity has increased in mainland China. With the aim of better understanding the influence of climate background on drought events in this region, we analyzed the role of the drought-related factors and extreme climate in the formation of droughts by investigating the relationship between the drought severity index (denoted as GRACE-DSI) based on the terrestrial water storage changes (TWSCs) derived from Gravity Recovery and Climate Experiment (GRACE) time-variable gravity fields and drought-related factors/extreme climate. The results show that GRACE-DSI was consistent with the self-calibrating Palmer Drought Severity Index in mainland China, especially for the subtropical monsoon climate, with a correlation of 0.72. Precipitation (PPT) and evapotranspiration (ET) are the main factors causing drought events. However, they play different roles under different climate settings. The regions under temperate monsoon climate and subtropical monsoon climate were more impacted by PPT, while ET played a leading role in the regions under temperate continental climate and plateau mountain climate. Moreover, El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) events mainly caused abnormalities in PPT and ET by affecting the strength of monsoons (East Asian and Indian monsoon) and regional highs (Subtropical High, Siberian High, Central Asian High, etc.). As a result, the various affected regions were prone to droughts during ENSO or NAO events, which disturbed the normal operation of atmospheric circulation in different ways. The results of this study are valuable in the efforts to understand the formation mechanism of drought events in mainland China. Full article

The Aral Sea basin is the most active source of salt-dust storms in the central Asian region, while its exposed bottom is acting as a “distributer” of salts and chemicals over the adjoining areas. In this study, the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT-4) is used to identify the trajectories of air parcels from the dried bottom of the Aral Sea region (45.40° N, 61.30° E) that are potentially containing salt-dust and their probability of influencing the downwind area in the period of 2016–2020. The frequency of air parcel trajectory was mapped for six levels: 100, 300, 500, 1000, 2000, and 3000 m agl. The trajectories were categorized by k-means clustering into four clusters that are named by their direction of movement as follows: Cluster 1: E category, Cluster 2: NE category, Cluster 3: W category, and the Cluster 4: S category. The 72 h of forward trajectories showed that salt-dust storms starting from the dried bottom of the Aral Sea had the highest probability of affecting the northeastern region e.g., Siberian Plain, followed by the southern region e.g., Iran Plateau. Total number of trajectories within these two clusters (NE and S) accounts for 90% (or 413 days) of trajectories in examined days. The main area of influence of salt-dust is close to the source area. The potential transport distance of salt-dust particles increases with the height of the starting point. The surface wind, which results from the changes of the Siberian High (SH), has a major role in shaping the surface atmospheric circulation which determines the transport pathway of salt-dust particles over the Aral Sea region. The results of this study could be useful to forecast the potential occurrence of salt-dust storms in downwind affected areas and would also be helpful to understand the possible causes of salt-dust storms which can provide the scientific basis for mitigation of the negative impact of salt-dust storms on the environment and human health. Further research should be conducted by using monitoring data to confirm the deposition of dust and salt particles in those areas mapped by our study. Full article

Snow plays an important role in meteorological, hydrological and ecological processes, and snow phenology variation is critical for improved understanding of climate feedback on snow cover. The main purpose of the study is to explore spatial-temporal changes and variabilities of the extent, timing and duration, as well as phenology of seasonal snow cover across the large part of Eurasia from 2000 through 2016 using a Moderate Resolution Imaging Spectroradiometer (MODIS) cloud-free snow product produced in this study. The results indicate that there are no significant positive or negative interannual trends of snow cover extent (SCE) from 2000 to 2016, but there are large seasonal differences. SCE shows a significant negative trend in spring (p = 0.01) and a positive trend in winter. The stable snow cover areas accounting for 78.8% of the large part of Eurasia, are mainly located north of latitude 45° N and in the mountainous areas. In this stable area, the number of snow-covered days is significantly increasing (p < 0.05) in 6.4% of the region and decreasing in 9.1% of the region, with the decreasing areas being mainly located in high altitude mountain areas and the increasing area occurring mainly in the ephemeral snow cover areas of northeastern and southern China. In central Siberia, Pamir and the Tibetan Plateau, the snow onset date tends to be delayed while the end date is becoming earlier from 2000 to 2016. While in the relatively low altitude plain areas, such as the West Siberian Plain and the Eastern European Plain region, the snow onset date is tending to advance, the end date tends to be delayed, but the increase is not significant. Full article

Lake Baikal is located on the southern tableland of East Siberian Russia. The west coast of the lake has vast forest resources and excellent ecological conditions, and this area and the Mongolian Plateau constitute an important ecological security barrier in northern China. Land-use/cover change is an important manifestation of regional human activities and ecosystem evolution. This paper uses Irkutsk city, a typical city on the West Bank of Lake Baikal, as a case study area. Based on three phases of Landsat remote-sensing image data, the land-use/cover change pattern and change process are analyzed and the natural factors and socioeconomic factors are combined to reveal driving forces through the partial least squares regression (PLSR) model. The results show the following: (1) From 2005 to 2015, construction land expanded, and forestland was converted into construction land and woodland. In addition, grass land, bare land, and cultivated land were converted into construction land, and the woodland area increased. The annual changes in land use from 2005 to 2010 were dramatic and then slowed down from 2010 to 2015. (2) The main reasons for the change in land-use types were urban expansion and nonagricultural development caused by population migration. The process of urbanization from external populations to urban agglomeration and the process of reverse urbanization from a central urban population to urban suburbs jointly expanded urban construction land area. As a result, forestland, grass land and bare land areas on the outskirts of cities were continuously reduced. After the disintegration of the Soviet Union, land privatization led to a decline in the farm economy, the emergence of agricultural land reclamation and urban expansion; in addition, the implementation of the “one-hectare land policy” intensified development in suburban areas, resulting in a reduction of forestland and grass land areas. The process of constructing the China-Mongolia-Russia Economic Corridor has intensified human activities in the region, and the prevention of drastic changes in land cover, coordination of human-land relations, and green development are necessary. Full article

Permafrost exerts strong controls on forest development through nutrient availability. The key question of this study was to assess the effect of site conditions on macroelement concentration and stable isotope (δ¹³C and δ¹⁵N) dynamics during the growing season, and nutrient stoichiometry and resorption efficiency in the foliage of two common larch species in Siberia. Foliar nutrient (N, P and K) concentrations of larches grown on permafrost soils were exceptionally high in juvenile needles compared to those from a permafrost-free region (+50% and 130% for P and K), but were two-fold lower at needle maturation. Within permafrost terrain trees, sites with a warmer and deeper soil active layer had 15–60% greater nutrient concentrations and higher δ¹⁵N in their needles compared to shallower, colder soils. Larch of permafrost-free sites demonstrated an enrichment of foliage in ¹⁵N (+1.4% to +2.4‰) in comparison to permafrost terrain (−2.0% to −6.9‰). At all sites, foliar δ¹³C decreased from June to August, which very likely results from an increasing contribution of current photoassimilates to build foliar biomass. With senescence, nutrient concentrations in larch needles decreased significantly by 60–90%. This strong ability of larch to retain nutrients through resorption is the essential mechanism that maintains tree growth early in the growing season when soil remains frozen. The high resorptive efficiency found for K and P for larches established on permafrost suggests nutrient limitation of tree growth within the Central Siberian Plateau not only by N, as previously reported, but also by P and K. The increasing nutrient concentrations and a ¹⁵N enrichment of foliage towards warmer sites was paralleled by an up to 50-fold increase in biomass production, strongly suggesting that accelerated nutrient cycling with permafrost degradation contributes to an increased productivity of Siberian larch forests. Full article

The widely distributed glaciers over the Qinghai-Tibet Plateau (QTP) represent important freshwater reserves and the meltwater feeds many major rivers of Asia. Glacier change over the QTP has shown high temporal and spatial variability in recent decades, and the driving forces of the variability are not yet clear. This study examines the area and thickness change of glaciers in the Dongkemadi (DKMD) region over central QTP by exploring all available Landsat images from 1976 to 2013 and satellite altimetry data over 2003–2008, and then analyzes the relationships between glacier variation and local and macroscale climate factors based on various remote sensing and re-analysis data. Results show that the variation of glacier area over 1976–2013 is characterized by significant shrinkage at a linear rate of −0.31 ± 0.04 km²·year⁻¹. Glacier retreat slightly accelerated in the 2000s, and the mean glacier surface elevation lowered at a rate of −0.56 m·year⁻¹ over 2003–2008. During the past 38 years, glacier change in the DKMD area was dominated by the variation of mean annual temperature, and was influenced by the state of the North Atlantic Oscillation (NAO). The mechanism linking climate variability over the central QTP and the state of NAO is most likely via changes in the strength of westerlies and Siberian High. We found no evidence supporting the role of summer monsoons (Indian summer monsoon and East Asian monsoon) in driving local climate and glacier changes. In addition, El Niño Southern Oscillation (ENSO) may be associated with the extreme weather (snow storm) in October 1986 and 2000 which might have led to significant glacier expansion in the following years. Further research is needed to better understand the physical mechanisms linking NAO, ENSO and climate variability over the mid-latitude central QTP. Full article