Using the isotope Atmospheric Water Balance Model (iAWBM), the spatial distribution and the temporal variations of δ18O in atmospheric vapor and in precipitation, and the correlations between δ18O in precipitation and precipitation amount and temperature in 2012 are simulated, in order to examine the capability of iAWBM simulating the water isotope cycle, to deal with the main causes of isotope effects and to improve the understanding of isotope effects in the water cycle. The simulated results reproduce well the latitude effect, continent effect and seasonality of δ18O in global precipitation. In the water cycle, the causes of producing the spatial and temporal variations of stable isotopes in precipitation are related to the isotopic enrichment in vapor due to evaporation, the isotopic depletion in vapor due to precipitation and isotopic depleted degree in vapor due to condensation temperature. The simulated precipitation amount effect, corresponding to the distributions of the seasonality of δ18O in precipitation and precipitation amount, occurs mainly in low-mid latitude oceans and monsoon areas. The simulated temperature effect, corresponding to the distribution of the seasonality of δ18O in precipitation, occurs mainly in mid-high-latitudes continents. However, along with strong amount effect, temperature effect also occurs in some low-latitude areas.
Based on data of meteorology and glacier ablation observed in 1959 and 2009, spatiotemporal variation of degree-day factor (DDF) on the Rongbuk Glacier in the Mt. Qomolangma of Central Himalayas was analyzed in this paper. It is found that DDF increased with altitude; the values of DDF at 5 260 m a.s.l., 5 350 m a.s.l., 5 450 m a.s.l., 5 500 m a.s.l. and 5 750 m a.s.l. were 3.27, 8.21, 23.19, 46.41 and 42.05 mm·℃-1·d-1, respectively. DDF varied less temporally for the same observational site. There was a few difference of DDF between observational sites with different thicknesses of debris. Generally DDF was less than 10.5 mm·℃-1·d-1 on both northern and southern slopes of the Himalayas at the altitude below 5 350 m a.s.l. When altitude was higher than 5 350 m a.s.l., DDFs on northern slopes of the Himalayas were larger than those on southern ones, with higher DDF in both slopes of the Himalayas (more than 15.8 mm·℃-1·d-1 in most areas).
As the result of the complex earth-atmosphere exchange system, permafrost will be inevitably influenced by climate change characterized by temperature rising. Based on ground temperature data from eight ground monitoring sites from 2006 to 2011, variation characteristics of permafrost temperatures and permafrost tables in cold and warm permafrost regions were studied in this paper. It is found that permafrost along the railway has experienced a significant warming. During the observation, the average rising rates of permafrost temperatures at 15-m depth and at permafrost table were 0.018 ℃·a-1 and 0.015 ℃·a-1, respectively, and the rising of permafrost temperature at the above two depths in cold permafrost regions was higher than that in warm permafrost regions. Moreover, the depth of permafrost table also showed an increase with a mean rate of 4.7 cm·a-1. The increase of permafrost table in cold permafrost regions was lower than that in warm permafrost regions. Response to climate change showed a great difference between cold and warm permafrost regions. Meanwhile, influenced by local factors, increases of permafrost temperature and permafrost table also showed some differences in different regions.
In seasonally frozen soil regions, as the internal structures of soil changing periodically under freezing-thawing cycle, the porosity and permeability of the soil change inevitably. In this study, a series of freezing-thawing cycle experiments of original and remolded loesses were conducted, followed by infiltration experiments. The results of these experiments show that the original and remolded loess's dry densities increase frist, then decrease and finally reach a steady state with increasing freezing-thawing cycles. Because of the negative linear relationship between dry density and coefficient of permeability, the permeability coefficient decreases first and then increases after 10 freezing-thawing cycles, finally reaches a stable value of between 4×10-4 and 6×10-4 cm·s-1. Because the remolded loess has been disturbed and the particles in structure are homogeneous while the original loess is not disturbed and the particles in structure are unhomogeneous, the permeability of remolded loess is always greater than that of original loess.
In this paper, triaxial compression tests on saline frozen silty sand were done at temperature of -2, -4 and -6 ℃, respectively, and under confining pressure ranging from 0.3 to 16 MPa. The outcomes of the experiment reveal that stress-strain curves show strain softening characteristics under low confining pressures and high confining pressures, and present ideal plastic deformation characteristics under intermediate confining pressures. As confining pressure increasing, strength would in the first place increase and then drop off. The generalized cohesion and the generalized friction angle are achieved in a limited range of confining pressure by the experiment and their variations with temperature and confining pressure are attained. Finally, considering the change of strength with confining pressure, a nonlinear strength criterion is put forward.
The physical properties of frozen soil in the embankment are impacted by environmental temperature. So, the deformation field and stress field of embankment will change seasonally. In this paper, the deformation field and stress field of a typical section of Qinghai-Tibet Railway in cold region are simulated and analyzed. Two conditions are considered namely with train passing and without train passing. The following conclusions can be drawn: 1) After the embankment construction, instantaneous deformation will occur under the gravity of soil. The deformation will change with time. The change tendency of the time-history of deformation is nearly negatively correlated with that of the time-history of temperature; 2) The vertical displacement of embankment will gradually decrease along the direction from the surface to the inner part of the embankment, no matter there is train passing or not. The maximum vertical additional deformation takes place at the center point of the embankment top. The additional deformation values are -4.94 mm, -3.24 mm, -2.56 mm, respectively, on Oct. 15, Jan. 15 and Apr. 15. For the center points at the embankment bottom and shallow layer of ground foundation, the additional stress is largest at Oct. 15 and smallest at Apr. 15. The maximum additional stress can reach 19.48 kPa. The influence of train load on the stress distribution in the upper part of embankment is larger than that in the lower part.
Silty sand with high ice/water content was tested under uniaxial compression on the basis of the previous method of specimen preparation and unifying the weight ratio of ice to water. It is found that uniaxial compressive strength of frozen silty sand nonlinearly increases with increasing strain rate, but the increasing rate gradually decreases with the increase of strain rate, and the relationship between the uniaxial compressive strength and the strain rate can be described by a log function. In addition, the higher temperature is, the smaller the extent is, in which the strain rate governs the uniaxial compressive strength; the uniaxial compressive strength decreases with raising temperature and the decline's rate gradually decreases with raising water content. With increasing water content, the uniaxial compressive strength begins to increase nonlinearly, and finally approaches to that of strength of remolded ice, which is different from the early research and results in a doubt on the correctness of the method of specimen preparation by means of adding ice particles to guarantee high ice/water content of specimen.
Aeolian sand is one of the most important factors that are able to change the permafrost environment in the Tibetan Plateau. Thermal conductivity is the key parameter for predicting the effects of sand sediments on ground temperature of permafrost. The variation mechanisms of thermal conductivity of aeolian sand were studied with scanning electron microscope/energy dispersive X-ray. The granulometric analysis of grain shows that the grain size is in between 75-500 μm, well-distributed, without clay and gravel. The aeolian sand always forms sand dune without any regular shape in natural state, with large porosity, high grain roundness and good sorting. The grain surface has obvious impact craters, which noticeably increase the specific surface area and porosity. There is less mutual contact area between the dry aeolian sand grains and more pores filled by air, resulting in decrease of thermal conductivity. While the thermal conductivity will increase gradually when the pores are filled with water; the corresponding conductivity will go up continuously when temperature decreases below 0 ℃ and the water in the pores will be frozen gradually. The natural water content and thermal conductivity of aeolian sand are low in warm season, but they are high in cold season. Additionally, the aeolian sand is the granular matter with even and smooth surface and few cohesive soil, and has a loose clastic structure with lager porosity, all of which result in high permeability, good drainage, and poor ability of water retention, indicating that aeolian sand is a good filling material for mitigating frost-heave of infrastructure.
Based on the data of geological survey of environmental engineering in the major towns in the Bailongjiang River basin, Gansu Province, the landform, human activities and other influence factors in the study area are considered and analyzed. Slope, lithology, earthquake, river, precipitation and other evaluation indexes are selected, and the evaluation factors' weights are determined by combination of the information content method and AHP, and finally the geo-hazards assessment in the study area is implemented by the function of superposition and reclassification of GIS technology. The results indicated that the geological disasters are mainly distributed in the town (valley) areas with relatively dense population in the Bailongjiang River basin, where geological disasters are relatively concentrated, with more danger. While geological hazards are relatively sparse in the middle and high mountain areas, where agriculture and animal husbandry develop well, with less danger.
Based on the contrast between the measured monthly mean temperature anomaly and the simulated monthly mean temperature anomaly reconstructed with multiple regression analyses at Moyu Station, Muqi Station and Akdala Station, the accuracies of the multiple regression analyses are analyze through the means of the cross-validation based on MAE and RMSIE, M-K mutation tests and wavelet analyses. Similarly, based on the analyses of EOF the contrast between the measured monthly mean temperature data from 90 weather stations and the data interpolated and reconstructed from 105 weather stations in Xinjiang also show that there is high similarity in eigenvectors. Finally, it is found that the multiple regression analysis possesses higher accuracy. The reconstructed Xinjiang monthly temperature data have reliability same as the measured monthly temperature data, which could better reflect the characteristics and variation of the monthly mean temperature and provide basic data for climate change research.
Based on the observation of surface mass balance from 1980 to 2010 on the Glacier No.1 at the headwaters of the Ürümqi River, Tianshan Mountains, together with hydrological and meteorological data, the relationships between net ablation and climatic factors and between net accumulation and climatic factors during 1984-2010 are studied. In addition, characteristics of mass balances in different altitude ranges and their impact on runoff of the glacier are analyzed. It is found that in the Glacier No.1 mass balance is in a continuous deficit situation. A statistical analysis shows that the correlation coefficient is -0.16 between net accumulation and precipitation; the correlation coefficient is 0.61 between net ablation and annual mean air temperature; the correlation coefficient is 0.78 between net accumulation and the summer mean air temperature; in 2010 both annual net accumulation and accumulation area reached the minimum in the record since observation; in 2010 both annual net ablation and ablation area reached the maximum in the record since observation. 2010 was the strongest ablation year (bn=-1 327 mm), when the Glacier No.1 was totally in the ablation zone (ELA>4 484 m). Most notably, mass balances in various altitude ranges of the glacier, whatever in east branch or in west branch, were significantly different from those in previous years. These suggest that 2010 was a special year of mass balance and that mass balance of the glacier seems to enter a new stage. It is also revealed that the influence of air temperature on runoff is greater than that of precipitation.
Water resources from snow cover melting are the most important component of runoff in spring in the headwaters of the Irtysh River. To explore the influence of forest on snow melting in spring, three observation sites with different geomorphological types, including grassland, glade in forest and land covered by trees, were chosen to observe the snow melt processes during the snowmelt period of 2014 in the Kayiertesi River basin at the headwaters of the Irtysh River. The results indicate that the variation of snow water equivalent (SWE) does not agree with the snow depth change: the decrease in snow depth is ongoing, but SWE begins to fast reduce only when the daily mean air temperature is above 0 ℃. The discrepancy between SWE and snow depth is caused by densification of new snow. The forests have significant function of adjusting the air temperature. The air temperature averaged from 10 to 24 March was -2.5 ℃ in the grassland, higher than that in the land covered by trees (-5.4 ℃) and in the glade of the forest (-6.1 ℃). The air temperature diurnal range is relatively smaller in the fine day and close to forest. The duration periods of snow melting in grassland, glade in forest and land covered by trees are 20 days, 43 days and 35 days, respectively, with the average rates of snow melting of 2.1 mm·d-1, 1.5 mm·d-1 and 1.2 mm·d-1, respectively. In addition, a single tree also has extremely distinct effect on the surrounding snow cover melting process. The disappearance of snow cover below a tree-crown (Scene 1) is prior to about 10 days than that of snow cover outside a certain range from the tree-crown (Scene 2); the snow melting rate of Scene 2 is two times more than of Scene 1 because of shallower snow depth in Scene 1 induced by the tree interception. The snow melting rate is dependent on air temperature and radiation. When air temperature is below 0 ℃, the snow melting rate is sensitive to radiation, but the sensitivity gradually weakens with the rise of air temperature, and almost disappears when the daily mean air temperature is always above 0 ℃. It is also found that the snow melt mainly takes place in between 14:00-19:00 every day, with the melting amount over 50 percent of the daily snowmelt amount. These results are very useful for flood forecasting and water resource management and utilization.
Altay Mountains are the northern periphery of the central Asian mountain system and the southern periphery of the Asian Arctic basin, which makes those mountains ideal areas for analyzing climatic records relating to both westerly jet and polar air mass. Some fresh snow, regelation ice, river water and snow pit samples from the Monh Hayrhan Glacier, Altay Mountains, were collected in June 2010. These samples of δ18O and δD were determined and their d-excess values were calculated. It is found that δ18O of all the samples from fresh snow, regelation ice and river water increase with altitude. Based on the HYSPLIT air trajectory model, the reverse tendencies to different transmission sources of moisture at different altitudes were derived. At high altitude, water vapor evaporated from the Caspian might make the biggest contribution to the snow, while at low altitude most of the water vapor might come from Arctic or West Siberia. On the other hand, the high d-excess in all samples indicate that, at least in the early summer of 2010, the re-evaporated vapor makes a great contribution to the precipitation in the study area. The mean backward trajectories show that during this time vapor sources in the study area are mainly related to the evaporation over West Siberia, one of the largest wetland in the world.
Large-scale (>10×104 km2) watershed modeling is facing many challenges at present. There are bottlenecks in the understanding and mathematical expression of the process, the scale transformation and the coupling mechanism of eco-hydrological processes. The modeling method based on ontology may spli the existing model into components according to multistage process represented by ontology. Then it is able to add component and to get custom model based on demand. Through semantic recombination and technological innovation, a new method is provided for large-scale river model integration. In this paper, the eco-hydrology in the Heihe River basin is taken as an example. After explaining the connotation of eco-hydrological ontology and analyzing the existing ontology building methods, the eco-hydrological ontology construction method is put forward based on knowledge, which is proved to be effective and feasible through constructing an ontology of desert ecosystem.
Bioremediation is related to indigenous microbial community dynamics, structure, and function. In permafrost areas of Northeast China, the potential application of bioremediation has been considered before the construction of the China-Russia Crude Oil Pipeline. So far less is known about the behavious of cold-adapted degrading bacteria in the permafrost along the pipeline. Therefore, a contamination experiment with crude oil was conducted for eight weeks to investigate the response of indigenous bacteria. The 454 pyrosequencing data obtained from the experiment revealed a clear shift in the bacterial profiles in contaminated samples by comparison with the innate communities. Proteobacteria (especially alpha and beta-subdivision) and Firmicutes were enhanced after the contamination. The population is dominated by members from the genera of Alicyclobacillus, Sphingomonas, Nevskia and Bacillus. This result is probably due to the eco-toxic effect of crude oil components, particularly PAHs which is in favor of the bacteria able to degrade or tolerant to aromatic compounds. In addition, the high loading of crude oil contaminants tends to result in more abundant bacteria able to withstand crude oil.
The seed germination rate of Prunus mongolica is up to 96%-98% when soil moisture content varies in between 4%-16%, without significant difference (P>0.05); when soil moisture content in between 4%-13%, germination index, vigor index, days of average emergence are significantly higher than that of 16% (P<0.01), and the most suitable soil moisture for the seed germination is from 4% to 13%; with increase of soil moisture, the height of seedling will increase, but the root shoot ratio and the sound seedling index will decrease, root length, seedling growth and dry matter accumulation will increase first and then decrease; the most suitable soil moisture content for seedling growth is 7%-16%; seedling drought resistance can be improved by lower soil moisture and be good for nurturing seedlings; with increasing of sowing depth, germination rate will decrease and the average days of emergence will increase and the rate of mergence will slow down; the most suitable sowing depth is 0 to 1 cm for ensuring full stand and 1-3 cm for sound seedling. The germinated seedling is dicotyledonous seedling of hypogeal germination.
Based on analysis of the connotation of urban natural disaster risk, a two-level evaluation index system is established to comprehensively evaluate the risk of urban natural disasters in Kashgar Prefecture, which takes the factors causing disaster, historical disaster records, exposure-vulnerability and disaster resilience in consider. A comprehensive evaluation model with multi indexes is used to analyze the urban natural disasters in Kashgar Prefecture. The data of 1991-2011 in the prefecture are quantitatively evaluated. It is found that during 1991-2003 the risks of urban natural disasters were fluctuated. However, since 2004, due to rapid social and economic development and other reasons, the disasters has occurred more frequently than before in the prefecture, which directly increases the risks of urban natural disasters. In this paper, countermeasures and suggestions are put forward on the basis of quantitative analysis to improve the risk management of urban natural disasters.