The accurate judgment on the depth of zero annual amplitude (ZAA) of ground temperature has significant implications for estimating permafrost evolution and determining the lower-boundary depth used in climate models, land surface models or hydrological models. Based on the analysis of ground temperatures observed in 15 typical monitoring boreholes on the Tibetan Plateau, the primary variation characteristics and impact factors on the depth of ZAA are revealed and a simplified method for calculating the depth of ZAA is put forward. The results showed that the average ZAA of low-temperature permafrost is 4.6 m more than the average one of high-temperature permafrost; the ZAA decreases with the increase of permafrost temperature, but there are several boreholes with high soil moisture content bored in low-temperature permafrost regions being having relatively smaller ZAAs. Due to the effect of dynamic of heat and water and freezing and thawing process occurred in the active layer, ground temperature changing depth has no significant correlation with annual ground temperature variation in the shallow layer (0.5 m in depth), but has significant positive correlation with temperature annual range near the permafrost table. The differences of thermo-physical parameters among boreholes at different regions are the main cause of significant regional difference and variation of ZAA; the ground water content, temperature, texture and water phase state play important roles in the variation of the thermo-physical parameters of geological media. Annual variation depth of ground temperature has no significant correlation with the shallow ground temperature changes (less than 0.5 m in depth), but has significantly positive correlation with annual temperature range near the permafrost table; the differences in thermal diffusivity of stratum medium are the main reason for annual ground temperature changing depth with regional difference; the change in soil moisture content, temperature, texture and phase state of water is an important factor affecting thermo-physical properties.
The characteristics of snow cover, the number of snow cover days and the snow cover depth in the Taibai Mountains were analyzed by using the snow cover land observation data in Taibai Weather Station from 1962 to 2014 and the observation records of alpine snow cover in Taibai and Meixian Weather Stations from 1980 to 2014, as well as satellite remote sensing data from 1988 to 2010. The results showed that in the western middle mountain zone of the Taibai Mountains the snow cover beginning day had delayed, the snow cover ending day had advanced, the duration from snow cover beginning date to snow cover ending date had reduced, the annual days and depth and area of snow cover had presented a decrease tendency from 1962 through 2014. The same variation had also taken place in the western middle and high mountain zones of the Taibai Mountains from 1980 through 2014, with annual snow cover day decreasing rate of 3.2 d·(10a)-1 and 8.9 d·(10a)-1, respectively, in the middle and middle and high zones. The change of snow cover beginning and ending dates and the snow cover days had varied not so obviously from 1980 through 2014. Analyzing the satellite remote sensing monitoring data showed that the snow cover area has decreased in the undulation in the Taibai Mountains. Correlation analysis revealed that there was a close relation between temperature and cumulative snow depth in the western middle mountain zone of the Taibai Mountains from 1962 through 2014. It is clear that the temperature rise is the main reason of precipitation decreasing and the accumulative snow depth decreasing. There were few snow cover days in July in the middle and high mountain zones during 1980-2014, and one of eight sights in Guanzhong, saying "the snow accumulation in lunar June (July in the Gregorian calendar) on the Taibai Mountains" in history, couldn't be presented in the mountains.
Monthly snowfall data in winter (December to February) from 55 weather stations in the Tibetan Plateau from 1971 through 2011 were analyzed to reveal the variation characteristics of the winter snowfall over the plateau. The distribution of the winter snowfall over the Tibetan Plateau is characterized by more in the east and south and less in the northwest and the middle Brahmaputra. The distribution of the relative variability and the distribution of snowfall are almost on opposite, with large relative variability. Bounded by 30° N, the plateau snowfall has opposite tendency between the north and the south. That is, snowfall increases in north and decreases in south. Based on the snowfall partition through applying rotated empirical orthogonal function, combined with correlation analysis, the evolution characteristics and long-term climate trend of the plateau snowfall during the last 40 years were analyzed. The following conclusions can be drawn:Snowfall distribution clearly reflects the geographical features and climatic characteristics of the Tibetan Plateau. That is, more snowfall in southern windward and the interchange zone of warm air and cold air, less snowfall in the leeward and north. During the last 40 years, the snowfall has shown from less to more, and then to less. It was significantly abundant from 1980 through 1990. An abrupt change from less snowfall to more had taken place in the mid-1970s. Mutation phenomena with snowfall reduction occurred respectively in 2007 and 1988 in two southern parts. Snowfall has significant periodic variations, a quasi-decadal variation (14 years) and a quasi-eight-year variation.
Base on the snow cover data, meteorology data of the Qinghai Plateau from 1961 through 2013, the spatiotemporal change of the days with snow cover was analyzed by REOF method and multiple regression to explore the seasonal relationships between the days with snow cover and temperature and precipitation. The following main conclusions are drawn:(1) During the 53 years the days with snow cover in the Qinghai Plateau had first increased and then decreased; from 1961 to the end of the 1990s an increasing tendency had presented, with a peak of 44-d in 1982, then from 2000 to 2012 a decreasing tendency had presented. (2) Spatially, snow cover distribution in the Qinghai Plateau was uneven, which can be divided into six climate zones. In the southern highlands the duration of snow cover was longest with an increasing tendency; in the eastern agricultural district and west (Qaidam basin), snow cover lacked with a decreasing tendency. (3) Temporally, the duration of snow cover had increased in winter and spring, especially in winter, but decreased in autumn. (4) Seasonal mean temperatures had increased, which was the key factors impacting the snow cover in autumn and spring. It is found that winter and spring precipitation had increased, thus the plateau in winter and spring had more moisture.
Snow cover in the Tianshan Mountains is an important water resources of Xinjiang Uygur Autonomous Region. Topography plays a major role in spatial distribution and accumulation and melt processes of snow cover, so there is an important theoretical significance to analyze the effect of terrain. Based on the eight-day synthetic data of snow cover (MOD10A2) during 2005-2014 from MODIS/Terra and the digital elevation model (DEM), the seasonal variation of snow cover in the Tianshan Mountains with elevation, slope and aspect was analyzed. The results show that:(1) accumulating and melting of snow occur all the time. In spring and winter, snow cover changes in the low and high altitude ranges more than that in the middle altitude range. In summer and autumn, the change occurs more in the middle altitude range. (2) Seasonal snow accumulating and melting occurs in different slopes all the time. Snow accumulating and melting have a linear relationship with slopes in spring and winter, which change significantly in the area with gentle and steep slopes. However, there is only a little change in summer and autumn. (3) There is symmetry and periodicity in the variation of snow cover in the Tianshan Mountains with the aspect. The change of snow cover mostly appears in the northern slopes in spring and winter, but the opposite case appears in summer and autumn. The change of snow cover is greater in summer and autumn than in spring and winter. This result could provide scientific basis for forecasting snow melting flood.
The precipitation data from 69 meteorological stations over the Tibetan Plateau from 1961 to 2010 are analyzed by using REOF (Rotated Empirical Orthogonal Function), linear trend analysis and cumulative anomaly methods. The spatial-temporal variability characteristics of the precipitation during last five decades are also analyzed, and the differences in precipitation change over the Tibetan Plateau are revealed as well. The results show that:1) from 1961 through 2010, the annual precipitation in the plateau had been increasing with an increasing rate of 6.7 mm·(10a)-1. 2) The seasonal distribution of precipitation is uneven over the plateau. Wet and dry seasons are obvious and precipitation mainly concentrates in rainy season. 3) Spatially, precipitation decreases from southeast to northwest with altitude increasing and topography changing, and inter-annual variability has diversified characteristics with diversification in interannual variation. 4) The entire plateau can be divided into ten zones of different features by REOF method. Among them, there are eight zones have increasing precipitation tendency, but decreasing precipitation tendency takes place in northeastern Qinghai Province and southeastern Qinghai Province-northern Sichuan Province.
Based on soil moisture dataset from US Climate Prediction Center and precipitation and temperature data from 80 meteorological stations over the Tibetan Plateau, in this study, the temporal-spatial variations and abrupt change of soil moisture were investigated along with the relationship between soil moisture and precipitation and temperature respectively. Result shows that soil moisture over the Tibetan Plateau decreases from southeast to northwest and it has a good corresponding correlation with precipitation in spatial distribution. But there is a time lag of 2-4 months between soil moisture and precipitation. The soil moisture over the Tibetan Plateau had presented significant increase during 1980-2012, and an abrupt change occurred in 2003. Precipitation and temperature, especially precipitation from May to October and temperature from January to June, have obvious effect on the process of soil moisture variation. Soil moisture during high water period is determined by precipitation while soil moisture during low water period is decided by both temperature from January to June and soil moisture during high water period.
As a "water tower of Asia", the Tibetan Plateau has a large effect on East Asian and even global water cycle. The degrading alpine wetland over the plateau, working as an assurance of plateau ecological diversity, is an important origination of water and surface runoff, where land-air water exchange not only reflects the regional climate change, but also has great significance for ecological environment protection. The one-year data observed with 10-minute interval at Longbaotan wetland in the source area of the Yangtze River was analyzed by the method of the FAO Penman-Monteith to look for the evapotranspiration change over the degraded alpine wetland and its relationship with environmental factors. The results showed that 1) during the grass growth season, the potential evaporation had distinct diurnal and monthly changes; the actual evapotranspiration was low in winter and high in summer with a peak in summer; 2) during the observation period, there was heavy water loss due to evapotranspiration exceeding precipitation; 3) soil temperature exerted an impact on the evaporation process; the soil temperature at 5-cm depth correlated more significantly with evaporation; the increase in soil moisture could provide plenty of moisture for evaporation process; 4) during a year, temperature is the key factor influencing the actual evapotranspiration; but in a sunny day during grass growth period, the evapotranspiration and radiation varies in the almost same pattern, and surface air temperature has less influence on the evapotranspiration, which correlates negatively with the relative humidity near surface.
Based on hourly precipitation data from 1961 through 2014 in Heilongjiang Province, variations of precipitation, precipitation frequency and precipitation intensity in flood season (May-September) are analyzed. It is found that the precipitation in the flood season was 430.0 mm, the precipitation frequency was 297.2 hours, the precipitation intensity was 1.2-1.7 mm·h-1 and the precipitation intensity had increased obviously. The precipitation change trend and precipitation frequency in most stations were not obvious, but 39% of stations had changed obviously in precipitation intensity. The diurnal variation of precipitation showed a single peak, more than half of the precipitation had concentrated in 11:00-22:00; diurnal variation of precipitation frequency was bimodal, in 00:00-04:00 and 13:00-19:00; the diurnal variation of precipitation intensity also showed a single peak, with high value interval concentrated in 13:00 to 18:00. In the province, short duration precipitation had advantage obviously, accounted for 46.7% of the total, with rainfall duration accounting for 49% of all rainfall duration; continuous 5-6 hours precipitation intensity was the strongest one, followed by continuous 3-4 hours one, and the continuous 1-2 hours one was the weakest.
Global climate change has a significant impact on the occurrence of extreme weather events, such as heavy rain and floods. Distinguishing features of temporal and spatial variation of rainstorm events in the background of climate change is the key to response the heavy rain and flood disaster. In this paper, the Huai River basin is taken as the study area. Based on the hourly precipitation data of 229 meteorological stations from 1951 to 2012, the study, combined with the theory of statistical and meteorology, using the Mann Kendall mutation test and moving t-test as well as IDW spatial interpolation method, has analyzing the temporal and spatial evolution of precipitation, duration, intensity and frequency of isolated rainstorm events in the context of climate change. The result shows that under the influence of climate change, the occurrence time of isolated rainstorm events appear a change tendency of extremer and wider, and the characteristics of the occurrence time of isolated rainstorm events appear obvious bimodal and moving backward phenomena. Moreover, the average duration of isolated rainstorm and the duration of isolated rainstorm attaining its peak intensities have increased, isolated rainstorm events of entire basin have increased too. Global climate change makes the frequency and the duration showing a rising trend in the basin, characterized by long duration and high frequency. Especially in the last 20 years, the high incidence rainstorm areas of the Huai River basin have expanded from some areas to the whole basin.
Based on the seasonal shift of the climatological-mean rainband along the northern rim of the West Pacific subtropical high, an intensity index for the rainband is defined. Regression analysis confirms that the index can well describe the intensity of the rainband. With the index it is found that the subtropical westerly wind impacts the intensity of the rainband substantially in early summer, but has no obvious effect on the intensity of rainband in midsummer. Further study suggests that in early summer the acceleration of the subtropical westerly wind against the air temperature field, which is low in the east and high in the west, strengthens the warm advection and then the ascent motion over the rainband. Hence the rainband is strengthened. In midsummer, the seasonal shift of the circulation over East Asia weakens the impact of the warm advection on the rainband intensity and the effect of subtropical westerly wind on the rainband intensity as well.
The Tenasserim Chain is the transitional zone between the southeast of Tibetan Plateau and Yunnan-Guizhou Plateau. Typical glacial erosion and sedimentary landforms of the late Quaternary can be identified in the study area higher than 4 200 m a.s.l. The glacial sequence with absolute ages not only can reconstruct evolutionary history of the Hengduan Mountain range but also provide critical basis for studying the effect of the uplifting mechanism of the Tibetan Plateau. According to the field investigation and ESR dating results, it is ascertained that the basic geomorphology features of the Quaternary glaciers and the glacial sequences in the study area. The results show that the glacial types were cirque glacier, valley glacier and piedmont glacier. There were four glacial advances in the middle Tenasserim Chain at least during the Late Quaternary. These glacial advances can be assigned to the Penultimate glaciation (MIS 6, MIS=Marine Oxygen Isotope Stage) during the Middle Pleistocene[(192±51)-(207±45) ka], the middle stage of the last glacial cycle[MIS 3, (55±8)-(54±9) ka], the last glacial maximum[MIS 2, (25±1)-(38±6) ka] during the Last Pleistocene and the neo-glaciation/Little Ice Age during the Holocene (MIS 1).
In recent years, remarkable progress has been made in Quaternary glacial-chronology with the development of several numeric dating techniques, such as cosmogenic nuclides (NC), optically stimulated luminescence (OSL) and 14C. In contrast, the dating of Quaternary glacial tills older than 100,000 years has been a challenge, because the present techniques have defects themselves. In addition, the sediments have been disturbed during transportation and sedimentation. Electron Spin Resonance (ESR) has advantages over these techniques. It can date moraine features older than 100,000 years or up to million-year scale. The mechanism to reset ESR time clock is fundamental for application of this technique in dating. A series of laboratory simulation and field observation studies were carried out. Researchers found that ESR signal intensity in germanium center of quartz grains detected from the manually ground samples would be decreased to 53%~69% of its original value, but would not be reduced to zero. If this residual signal could be determined and removed, the accuracy of ESR dating of glacial tills could be greatly improved. In the future, more research should be carried out to look into the mechanisms of dating, to improve the purity of quartz in test samples, and thus to improve the accuracy of ESR dating signal. Thus, ESR dating will become of the most independent and credible cross-dating methods and provide accurate dating of the ancient glacier tills for Quaternary glaciation research.
Based on the data of the Tibetan Plateau highway test project of the Chinese Academy of Sciences, air flow characteristics in the ventilation duct and variation are studied by numerical simulation. The study demonstrates that air flow characteristics are significantly different from place to place when the ambient wind velocity reaches a certain value, showing three sections obviously, i.e., the inlet turbulence section with strong turbulence intensity, the middle section with fully developed turbulent of weakest intensity, and the jet-influence section with the turbulence intensity in between the two sections before. With increase of the ambient air velocity, the air velocity within the duct increase nonlinearly. At the same time, the length and the intensity of turbulence activity in the inlet disturbed section increases significantly. In the jet-influence section, because of the influence of the air flow inertia, the length reduces by a nonlinear acceleration, and the vibration amplitude of air motion trajectory accelerates nonlinearly. The diversity of the air flow characteristics in different sections of the ventilation duct is the basic reason for the different in local heat transfer flux. The existence and further superposition of these flow characteristics would become an important factor for developing the different between the south-faced slope and north-faced slope.
Vertically buried pipes are often used to measure temperature field of frozen soil. In this study, iron pipe, PVC pipe, PE pipe and PPR pipe, which are often used in temperature observation, are investigated. It is found that there is significantly different among the temperature fields measured in pipes of different materials. Comparative tests of temperature measurements by the sensors placed inside the four types of pipe and a measurement by the sensors directly inserted into the soil were conducted from November 3, 2014 to April 29, 2015. The measuring depths were 5, 20, 40, 80, 120 and 160 cm. The measured soil temperatures in the pipes and directly in the soil were compared. The comparative analysis showed that:(1) Owing to the difference in physical properties, different materials of the pipes have different influence on the measured temperature field; the measured temperature in PVC pipe and PPR pipe are slightly higher than the true soil temperature about 0.8℃and 0.3℃, respectively, but that in PE pipe and iron pipe are slightly lower than the true soil temperature about 0.4℃ and 0.6℃ respectively; (2) After analysis and comparison, the measured temperatures in iron pipe, PVC pipe, PPR pipe and PE pipe are correlated with the true soil temperature with the order:iron pipe > PPR pipe > PVC pipe > PE pipe; (3) Using the least square method, transfer coefficient from the measured temperatures in iron pipe to the true soil temperature of each layer can be obtained. Thus, a fitted equation can be established between the measured temperatures in iron pipe and the true soil temperature, which is verified having significant correlation.
The tensile strength of rock depends on moisture contents and temperatures. In order to study the mechanical properties of sandstone sampled from Lanzhou, Brazilian splitting test was carried out to investigate sandstone's tensile strength under different temperatures (+20℃, -5℃, -10℃) and different moisture contents (dry, natural and saturated). The test results showed that the tensile strength of sandstone decreases sharply with moisture content, until it softens to disintegration and loses bearing capacity due to saturation. When temperature less than 0℃, the specimens at natural water state has tensile strength always higher than those at dry state. When temperatures change between -10℃ and +20℃, the tensile strength of dry rock increases with temperature, but the tensile strength of saturated rock reaches the maximum at -5℃. There are critical values for the moisture content and temperature effects, exceed the critical values, the relationship between the tensile strength of the rock and the moisture content or temperature will be inverted. These results will be useful for testing the tensile strength of rock and forecasting rock strength.
Migration processes and properties, quantitative evaluation, mitigation and remediation techniques of petroleum pollutants in permafrost regions need to research urgently. A series of laboratory experiments have been conducted for simulating and studying migration processes of petroleum pollutants in soils, which have subjected freeze-thaw cycles. The research mainly focused on the effects of freeze-thaw cycles on the migration processes by monitoring and analyzing the soil temperature distribution, the moisture distribution, total oil contents at different depths and oil components distribution in soil. The test results show that the freezing and thawing cycles influence the physical properties, the absorption effect of hydrocarbon contaminants by soil particles, distribution and phase state of water in soil specimens. In turn, it influences the migration processes of petroleum pollutants. These findings are useful for better understanding oil migration in permafrost regions, for quantitatively evaluating contamination range and for developing mitigation and remediation techniques.
Based on the observation of surface temperature (5-cm in depth) at K2968.2 of the Qinghai-Tibet Highway in Qumar River region on the Tibetan Plateau, the regression equations of the boundary temperature are fitted, and the differences in thermal state between south-facing and north-facing slopes of the railway and highway embankments are analyzed. It is revealed that the boundary temperature regression equation has high fitting degree, which can be used to numerically simulate the frozen soil embankments. The monitoring section of highway and railway embankments shows significant differences between south-facing and north-facing slopes. The temperature difference between the left and right slopes of the highway is 11.49℃ in winter, and its annual mean value is 4.77℃. The temperature difference between right and left embankment toes reaches 5.34℃ in winter, with an annual mean of 3.33℃. The difference between the mean annual original surface and air temperatures is 5.2℃. Looking from Freeze/thaw n-factors, with a lower freezing n-factor and a higher thawing n-factor, the south-facing slope exhibits an endothermic behavior; on the contrary, the north-facing slope shows exothermic effect. However, in the north-facing slope, there is a larger freezing n-factor, resulting in exothermic effect. There is basically the same changing tendency of solar radiation and temperature change on embankment slopes.
The calculation methods of dynamic elastic modulus and damping ratio of soil were discussed on basis of visco-elastic theory. According to the result of a series of tri-axial test on frozen clays sampled along the Qinghai-Tibet Railway, suggestions about how to calculate the dynamic parameters were put forward. The result shows that the backbone curve of frozen clay is not a hyperbolic one. The dynamic elastic modulus and dynamic strain amplitude can be calculated through hysteresis loop, and then revealed their relationship. The relations between damping ratio and dynamic strain amplitude calculated with different methods are the same. The damping ratio under the lag angle method is less than that under the energy loss method. The lag angle of strain and stress can be obtained from correlation function method. It is recommended that using correlation function method to calculate the lag angle between strain and stress, and using the lag angle to calculate the damping ratio. The damping ratio of frozen clay increases with dynamic strain amplitude.
The compressive strength and tensile strength of frozen soils are two important mechanical indexes for designing engineering structures in cold regions. In this paper, uniaxial compressive strength test and splitting test of silty clay, silt and sand at the temperatures below 0℃ were carried out to study the failure mode and mechanism of frozen soil, the forms of stress-strain curves and the curves of tensile stress and radial displacement, and to analyze the difference between compressive strength and tensile strength and to reveal the dependence of the two strengths on soils and temperatures. Experimental results showed that the specimen has a drum-shaped deformation under uniaxial load and all behaves as strain softening and plastic collapse characteristics. Cracks occurs along with diameter to sides under the action of splitting; the width and depth of cracks are dependent on soil behavior. There is a good linear relativity between compressive strength, as well as tensile strength, and temperature; the strengths increase with decrease in temperature. The compressive strength of frozen soil is greater than its tensile strength at the same temperature. For the same frozen soil, the temperature effect for compressive strength is stronger than that for tensile strength. The datum and results of the experiment are helpful for engineering in cold regions.
Based on runoff and precipitation data of nearly 30 years over the Juntanghu River basin on the northern slopes of the Tianshan Mountains, using Kendall correlation method, R/S analysis, methods of precipitation-runoff accumulated hyperbolic curve and so on, the annual and seasonal runoff variation characteristics and influence factors of the Juntanghu River are discussed. Results show that annual runoff distribution is uneven, mainly concentrating in spring. The decadal variation of runoff has been significantly rising, with an increasing rate of 0.0015 m3·s-1·a-1 and a Hurst index of 0.6326. Seasonal variation shows different changing trends, a decreasing trend in spring and autumn and an increasing trend in summer and winter. In recent years, due to the influences of human activities and natural features, runoff and precipitation accumulation curves have showed a certain deviation, with the contribution rate of human activities to runoff of 25.68% and the maximum contribution rate of precipitation to runoff of 74.32%. Thus, precipitation is the main factor influencing runoff variation of Juntanghu River, followed by human activities.
Because of the regulating effect of frozen ground in infiltration and runoff generation, the effect of frozen ground is essential to understand the hydrological process in alpine regions. To quantitatively assess the changing trends of runoff owing to climate change and to understand the underlying mechanisms in the hydrological process in alpine regions, it is necessary to explicitly integrate the processes of ground freezing and thawing into traditional distributed hydrological models. In this paper, the physically based simultaneous heat and water frozen ground model is coupled into the geomorphologic-based distributed hydrological model. After a simple validation in the Baba River basin, a sub-basin in the upper reaches of the Heihe River, the model was used to analyze the influences of frozen ground on the runoff and discharge. The results show that the model appears to be acceptable and frozen ground has significant influences on the runoff generation. In the base model with a frozen ground module, subsurface runoff is dominated and the river runoff responses quickly to rainfall and snowmelt, which results in violent variation. In addition, notable surface runoff due to excess infiltration occurs at high elevations. When the frozen-ground module do not be considered, the simulated groundwater and base flow will increase 3 times. At the same time, the simulated hydrograph was much smoothened and flattened, with delay in the occurring time and attenuation in the summer flood peaks. The simulated average depth, at which the subsurface runoff takes place, is about 2.4 m, deeper than that of 1.1 m simulated with the base model. In spite of some existing limitations, this study is still useful because it provides a theoretical and quantitative understanding in the influences of frozen ground on cold hydrological processes.
Based on the hydrological data from five hydrological stations located in the middle reaches of the Yangtze River from 1983 through 2014, the changing characteristics and long-term trend after the operation of the Three Gorges Reservoirs (TGR) were systematically analyzed with the method of Morlet wavelet and ARIMA model. The result shows that:(1) Since the TGR operation, a tiny annual change of river discharge in the typical sections in the middle reaches of Yangtze river have been detected, and an obviously homogeneous trend of discharge within an year have been seen owing to climate variation and human activities. (2) River runoffs of the five typical sections in the middle reaches of the Yangtze River change with obvious periods of 18-26 a and 8-13 a, with cycle centers of 22 a and 12 a, respectively, and also with shorter cycles. The operation of the TGR has impacted more on the short changing period than long period. (3) Generally, since 2014, runoff of the five typical sections has been continuously abundant. Runoff in Zhicheng Station has increased after 2014 till 2017; after a shift from drought to wet in 2011, runoff in Shashi, Jianli, Chenglingji and Luoshan Stations have increased. It is expected that a maximum runoff will reach in 2016, after that then, a decreasing tendency will show up; wet runoff in period, however, will remain until 2018.
Using the water samples collected in Yushugou River basin during July-August, 2013, the main chemical ions, pH value, electrical conductivity and total dissolved solid were analyzed systematically, and the sources and causes of the ions were discussed. The analysis results show that the river water was weak alkaline. The main anion and cation were HCO3- and Ca2+. The concentration of Ca2+ accounted for 69.45% in cations, and that of HCO3- accounted for 84.18% in anions. Thus, hydrochemical type of the river water was H2CO3-Ca2+. During the flood period, water chemicals contained in river water were partly effected by water dilution. Based on the comprehensive analysis by Gibbs Figure, triangular diagrams of anions and cations and main ion ratio method, it was revealed that the main source of major ion in water was rock weathering. Carbonate rock weathering was mainly controlled by weathering H2CO3 rock accompanied by a small amount of H2SO4at the same time. Rock weathering were mainly composed of calcite mineral dissolution.
In 2014, the surface water in Ebinur Lake region was sampled and its chemical characteristics and controlling factors in dry and wet seasons were determined with multivariate statistics and piper plot of anions and cations, as well as Gibbs graphs. The results indicate that both in May (wet season) or in October (dry season), Na+ and Cl- are the dominant ions, respectively, followed by Mg2+ and SO42-. In May, Na+ and Cl- account for 70.34% and 52.97% of the total cations and anions and in October, Na+ and Cl- account for 70.57% and 66.48% of the total cations and anions. The hydrochemical type of the surface water in Ebinur Lake region is dominated by weathering reaction and evaporative crystallization, thus as a result, in wet season it is HCO3--Ca2+-Na+ type and in dry season it is HCO3--Ca2+ type. In addition, the controlling factors for the ion components in the surface water were investigated. It is found that the weathering reaction and evaporative crystallization are the major natural factors that impact the hydrochemical composition of the surface water in Ebinur Lake region during both dry and wet seasons. The influence of atmospheric precipitation input is weak. According to the relative research, the population and regional gross domestic product (GDP) are the major human activity factors that affect the hydrochemical composition of the surface water. This investigation is useful for the study of river water chemistry and water quality and for the water protection in arid regions of China.
Hydrogen and oxygen isotope can be used to trace hydrological cycle effectively. Water is the key element to maintain the stability of Hani Terrace landscape. In this paper, the spring water from the Malizhai River basin was taken as the research object. The basin is located at the core area of Hani Terrace, a World Cultural Heritage. From the basin, spring water samples were collected at different altitudes to analyze altitude effect of the hydrogen and oxygen isotopes. The results indicate:(1) Overall, spring water oxygen and hydrogen isotope decrease with altitude, with a lapse rate increasing with altitude, and characterized by three section elevation differentiation. (2) The low elevation section (less than 1 060 m a.s.l.), and high elevation section (more than 1 510 m a.s.l.) have a significant altitude effect, but the middle-altitude section (1 060~1 510 m a.s.l.) has no significant altitude effect. (3) The relation equation of spring water's hydrogen and oxygen isotope has somewhat lower slope as compared with the national average, which indicates some impacts from rainfall, evaporation and replenishment to the spring water. (4) As regard to the deuterium excess, the deuterium excess value in low-altitude section is almost the same as the meteoric water line of China, while in the middle-altitude section, it is lower than the meteoric water line and in the high-altitude section, it is higher than the meteoric water line. To sum up, there is a strong mixing process within the spring water of the study area; the altitude effect of spring water's hydrogen and oxygen isotopes is due to the multiple water cycle as well as water use.
The spatial distribution of the response to temperature change of Altay Betula rotundifolia were studied by used GIS technology and fractal interpolation method based on long series of remote sensing data. The results showed that:(1) In the last 24 years, temperature in the Altay Mountains has risen with the rate of 0.18℃ every ten years, Betula rotundifolia cover area has grown 7.28%, Betula rotundifolia has significantly grown with temperature, and the faster the temperature rising, the faster the Betula rotundifolia cover area growing; (2) Along with temperature rising, the average elevation of Betula rotundifolia distribution has risen, temperature rising not only expands Betula rotundifolia cover area, but also rises average altitude of Betula rotundifolia distribution and temperature varying at higher elevation has more effect on vegetation growing; (3) With temperature increasing, Betula rotundifolia cover area has increased at all exposures, especially, on the sunny sides.
In order to explore the response of desert plant growth to soil water in desertification control, the Experimental Station of Desertification Control in Hongshawo had been set up in the desert district of Hexi Corridor in order to obtain long-term monitoring data about precipitation, soil moisture, groundwater depth, vegetation biomass and coverage. The algorithm of characteristic parameters, correlation and multiple regression analyses had been applied to study the response characteristics of plant growth and annual and monthly water variations. The study has found that:(1) the change in soil moisture content was very severe, the changes in precipitation, biomass and coverage were severe with same extent, but change in groundwater depth was minimal. The change in coverage showed an increasing tendency in the undulation, but changes in biomass slightly increased. The changes in precipitation, soil moisture content and groundwater depth decreased slightly; (2) in the growing season from March to November, the soil moisture content variation was basically in the same step and so did the changes in average vegetation coverage and biomass; (3) the regression equations about coverage and biomass have passed the R fitting test, F test, t test for partial regression coefficient. Through the model, it is possible to predict coverage of 58.0% and biomass of 98.7%, with accuracies of 52.0% and 86.2%, respectively. This study results will be useful for water resource management and for evaluating the effect of desertification control (such as engineering of returning farmland to forest, natural forest protection and comprehensive reclamation) in the middle reaches of the Heihe River on water resources.
Based on in-situ expedition, by using historical document and statistical analysis, the natural vertical zones of Tianshan Tomur Nature Reserve were analyzed in this paper. The following conclusions can be drawn:(1) Hydrothermal conditions controlled by topographic factors are basic for the formation of natural vertical zones in the study area, followed by latitude; Hydrothermal conditions restricted by terrain factors are the most important material and energy sources for the formation of vertical belt landscape; with the vertical changes of hydrothermal conditions, various vertical belts regularly appear from low mountain to alpine zone; they are warm desert zone, temperate desert steppe zone, mountain steppe zone, subalpine meadow zone, alpine meadow zone, alpine cushion vegetation zone and alpine snow-ice zone. (2) The eastwest trending Tianshan Mountains, characterized by north-south deep excavation glacial and fluvial landforms, act as a barrier to the moist air flow from the North Atlantic and Arctic Ocean, resulting in the southern and northern slopes of the Tomur Peak having different climate characteristics:warm temperate semi-arid and arid climate forming on the southern slopes. The natural landscape is dominated by temperate desert, desert steppe and grassland, the plant species are poor and had drought tolerance characteristics; along with the increasing altitude, the desert elements of the plant has gradually decreased, the composition of grassland and meadow gradually has increased, the organic matter content of soil has increased, thus the leaching of carbonate has increased.
The purpose of this study is to assess the distribution and variation trend of ecosystem services values with terrains in Shaanxi Province. Land use status was evaluated on the basis of land use information and DEM data of 2000 and 2010. The sequential variation as well as spatial distribution pattern of ecosystem services was quantitatively analyzed by reference to"ecosystem service value equivalent per unit area of Chinese terrestrial ecosystem" with ArcGIS. Simultaneously, eco-economic harmony index (EEH) of the province was also evaluated. It is found that from 2000 to 2010, the ecosystem service value had increased 1.09 billion yuan, among which ecosystem service value in forest land and grassland had increased 2.14 billion and 2.32 billion yuan, respectively, while that in cultivated land had decreased 3.42 billion yuan. As regards the terrain and gradient, ecosystem service value shows a decreasing tendency northwards and southwards from the center, and concentrates on the regions with gradient of 0°-14.6° and on the elevation ranges of 1 607-1 380 m. As for the single ecosystem service value, waste disposal and food production has severely decreased 0.61 billion yuan owing to sharp decline of cultivated land. The results of EEH show that the ecological economy in Shaanxi Province is tending to be no harmonious as a whole. Thus, it is of great necessity to put emphasis up on ecological environmental protection and economy development.
Logic regression model and spatial analysis technology were used to evaluate the suitability of land use in the Heihe mountain areas. An index system of evaluation was established, which included temperature, precipitation, digital elevation model, slope, population, water system, communication network and distribution of towns based on the land use data in 2011. The multi-scale training method was used to determine the best evaluation scale. Then, the contributions of all the evaluation factors were calculated based on the logic regression analysis. Spatial Analyst Module was used to evaluate the suitability of land use. The results show that:(1) the best scale of evaluation is 210 m (ROC=0.79); (2) slope and temperature (βTemp=1.11) play a very important role in the change of forest and grassland. In addition, the distance to roads and the density of population have a significant impact, with a β of -0.555; (3) the suitability ranks as forest land=cultivated land > settlements > nudation > grassland > water areas, with the value of suitability is 0.99 for forestland and cultivated land.
Agricultural ecosystem is a kind of artificial and natural complex ecosystem. Human behavior and management control will interfere the supply and demand of ecosystem services, which makes the relationship among ecosystem services also change. Taking Xi'an City as the research object, in this paper, the values of the supply of agricultural products, carbon sequestration, water conservation, environment cleansing and cultural services are measured and then the spatial differences within the total value of ecosystem services are analyzed. According to the landscape characteristics and the value of agricultural ecosystem services, in this paper, the study area is divided into three zones to explore the relationship among different functions of ecosystem services. At last, ecosystem management strategies in Xi'an City are put forward. The following conclusions can be drawn:(1) The total value of agricultural ecosystem services in the city is 59.0 billion yuan. From the view of ecosystem service classification, regulating services are larger than supply services, and supply services are larger than cultural services, with a great difference among various counties (districts). (2) On the whole, supply services had increased, while regulating services and support services had decreased of the city from 1999 to 2013. (3) The value of agricultural ecosystem services had increased generally form urban center to the edge zones. (4) Spatially, the correlations among various agricultural ecosystem services are quite different. Among farming area, garden and forest area, the correlations among supply services, regulating services and cultural services are different, while between regulating services and cultural services there is a significant positive correlation. (5) In order to maintain the stability of urban ecosystem, urban green space landscape pattern should be adjusted to "green patches, green corridors, wetlands, farmland" mosaic coexistence space ecosystem; It's necessary to adjust agricultural structure to develop ecological industry in the farming and garden areas, such as choosing varieties of crops and vegetation types of both the economic and ecological benefits.