In this study, the MODIS daily snow products without cloud contamination and AMSR-E snow water equivalent products were integrated to get snow water equivalent products of 500 m resolution in the Tibetan Plateau. Then these products were used to analyze the spatial-temporal changes of snow cover over the plateau during 2003-2010. The results showed that snow had accumulated mainly in the high mountains, with a little in the hinterland of the plateau. The snowfall had showed a very unevenly distribution spatially. The average snow-covered days (SCD) had showed a significant decreasing trend, the stable snow cover area had increased and the perennial snow cover area had shrunk during 2003-2010. The increasing regions of snow water equivalent (SWE) was similar to those of SCD, but in the Himalayas. In the Himalayas, the SCD had decreased but the SWE had increased, which mainly caused by more snowfall in winter. The overall snow-covered area (SCA) had showed a fluctuating deceasing trend, but not so significant and the decreasing proportion was very small. In contrast, the maximum of SCA had showed an increasing trend during 2003-2008 and then decreasing. The snow mass had showed a significant decreasing trend over the plateau during 2003-2010, with an annual decreasing rate of 1.0×103 m3·a-1.
Using the snow depth data from satellite (SMMR, SSM/I and AMSR-E passive microwave remote sensing), the temporal-spatial variation characteristics of the Tibetan Plateau (TP) snow depth inter-annual anomalies were analyzed with EOF. There are remarkable seasonal and multi-scales characteristics of the inter-annual anomaly regions of the TP snow depth. In the period of late fall to mid-winter (from October to January), the inter-annual anomaly regions locate in the hinterland and valley. The area of anomaly regions become small, meanwhile, the snow depth on the TP is almost unchanged during late winter to early spring (from January to April). However, the anomaly regions of the TP snow locate on the eastern TP with the rising of temperature in spring (from March to May). There is a seasonal variation of the snow depth inter-annual anomaly center in the TP on the local scale, which shows the opposite change between the inter-annual anomaly and the trend of inter-annual anomaly in the TP snow depth. The change of the anomaly maximum region of the TP snow depth indicated the feature that the snow depth on the TP is influenced by winter monsoon and warm wet stream from the south. Further, the TP snow depth has an obvious inter-decadal variation. The snow depth is maximum during the 1980s, then decreased later, but the maximum snow depth from late autumn to winter (from October to February) occurs in 1990s. The TP snow amount was large in the late of 1990s, and decreased after 2000.
Glacier change was investigated by using Landsat TM5 and glacier inventory from 1970 to 2009 in the Kaidu River Basin (KRB) in the southern slope and in the Manas River Basin (MRB) in the northern slope of the Tianshan Mountains. Then, combining with records from weather stations, the differences of glaciers and glacier change between the two basins are analyzed. It is found that there were 2 522 glaciers with glacierized area of 1 356.1 km2 in the study regions in 2009. And in the period of 1970-2009, glaciers had shrunk 494.33 km2 in area, accounting for 26.8% (0.8%·a-1); ice storage had decreased 32.73 km3, accounting for 27.9% (0.8%·a-1). Shrinking ratio of ice storage was slightly greater than that of glacierized area decreasing. In addition, both the area shrinkage and the storage decrease from 2000 to 2009 (1.3%·a-1) were larger than those from 1970 to 2000 (0.6%·a-1). The area shrinking ratios from 1970 to 2000 and from 2000 to 2009 were 0.5% and 1.4% in MRB, and 0.9% and 1.1% in KRB, respectively. Thus, the glacier shrinking acceleration was greater in MRB than that in KRB from 2000 to 2009. Based on climatic records, glacier retreat was mainly controlled by air temperature rising, and the differences in precipitation and temperature variations were the key factors to glaciers retreating in MRB slower than that in KRB.
Tibetan Plateau (TP), the study region of this paper, is defined as 74.75°~104.25° E, 26.75°~40.25° N. Based on the daily gridded surface air temperature data (0.5°×0.5°) and the data of the global monthly mean sea level pressure field, height field and wind field (2.5°×2.5°) from NCEP/NCAR reanalysis data from 1960 to 2010, the mean surface temperature in winter in the TP is calculated. The index of winter temperature in the TP is recognized as the standardized time series for the whole TP. The relationship between Arctic Oscillation (AO) in winter and the surface air temperature in the TP over the same period has been investigated. The results show that when the phase of AO is negative (positive), the westerly flow in the mid-high latitudes is weak (strong), which is conducive (not conducive) to drive the polar cold air southwards. It is shown that when the AO index is in low value period, the mean surface air temperature in winter in the TP is low also. M-K analysis on the AO mutation shows that the abrupt year was 1975. Significance tests at 500 hPa and 200 hPa height fields and wind field before and after the mutation year find that when the height field associates with high AO index in winter, at 500 hPa, the trough in the Eastern Europe shallows and the ridge in the northern TP weakens with zonal developing circulation, the north wind of middle troposphere is weak with higher air temperature, consistent with warm winter in the TP; at 200 hPa, the eastern trough over the east TP significantly deepens, resulting in meridional developing circulation between the tropopause and the end of the stratosphere.
By using wavelet transformation, multi-time scale characteristics and changing trend of the temperatures within the original ground and embankment in permafrost region at the Fenghuoshan monitoring site along the Qinghai-Tibet Highway are analyzed and predicted. The results show that permafrost temperatures within the original ground and embankment have multi-time scale characteristics, with different time-frequency distributions of multi-time scale; within the natural ground there is a simple regularity; within the embankment there is relatively complex situation, especially, near the permafrost table. Now permafrost temperatures within the original ground are in warm period, and deep permafrost temperatures enters cold-warm period lag behind that in shallow layers. The cold-warm period of shallow and deep permafrost temperatures is the opposite below the embankment, the length of cold-warm period is also not uniform. This could bring more hidden troubles to the stability of roadbed, but provide a new basis for treatment roadbed disease.
Investigation and study of periglacial landforms were done in the Mt. Laotudingzi in the center of the Laotudingzi National Nature Reserve in eastern Liaoning Province. It is found that the extensively developing periglacial landforms in this region involve block streams, rock glaciers, rock block fields, and occasionally, rock forts, nivation swales, gelifraction collapses and taluses. The gravel is not uniformed in distribution size and shape, and its deposition mode is chaotic, which has potential mobility under surface runoff. The effect of weathering and eluviation is most remarkable within rock glacier. The block stream is good at pedogenesis and rich in nutritive element content. Moreover, there is a specific landscape, under which subsurface stream forms, above which the vegetation cover is various, which can be classified as deciduous broad leaved forest, coniferous and broadleaved mixed forest, dark coniferous forest, krummholz, shrub and shrub-meadow, changing with elevation successively in accordance to the complexity of periglacial landform. In view of the severe environment, extremely tough vegetation succession in this region, human intervention is of utmost importance. It is suggested to consummate vegetation coverage and to promote succession process quickly, in order to improve the stability of this periglacial landform. It should be made it possible to maintain a balanced unity to protect environment, to promote the condition of vegetation and to stabilize the deposition of periglacial landform, so landform can be protected in a comprehensive way.
Precipitation is an important section in water cycle. Isotope ratios in precipitation are associated with the meteorological process, which display an obvious spatial and temporal distribution. Isotope ratios in precipitation can be used in deriving the atmospheric processes, tracing the vapor sources and reflecting the local weather and climate conditions. In order to study the spatial distribution of δ18O in precipitation over China, BW model are used to establish a model of the quantitative relationship between δ18O in precipitation and latitude or altitude. The model can be described as: δ18O= -0.024LAT2+1.541LAT-0.002ALT-29.678. Simultaneously, the residual of BW models with different methods are interpolated, and the interpolation accuracies are compared. Comparing to previous research, the RMSE of this method is reduced by 0.14‰ with ME close to 0. Finally the spatial distribution of residual of BW model with the most optimized method is made and a spatial distribution map of δ18O in precipitation over China is drawn, which provides important information for studying ancient climate and stable isotopic hydrology.
Based on the data of monthly mean precipitation and water vapor pressure from 43 weather stations in Qinghai Province from 1971 to 2010, the precipitable water (PW) and precipitation conversion efficiency are calculated by using an empirical formula of atmospheric total PW for the four ecological function regions, i.e., the eastern agricultural area, area of Three Rivers Sources, the area around Qinghai Lake and Qaidam Basin. The results show that the precipitable water of all ecological function regions presented a unimodal distribution form, with the maximum in the summer. The precipitation conversion efficiency over the area of Three Rivers Sources and the eastern agricultural area presented a bimodal distribution, but a unimodal distribution over Qaidam Basin and the area around Qinghai Lake. The precipitable water of all ecological function regions had increased during the 40 years, especially in Qaidam Basin and the area around Qinghai Lake. There were abrupt changes of PW in all ecological function regions; in the eastern agricultural area and Qaidam Basin abrupt change happened in 1983 and 1996, respectively; in the area of Three Rivers Sources and the area around Qinghai Lake abrupt change occurred in 1993. The PW had increased gradually from west to east, and the precipitation conversion efficiency had decreased towards Qinghai Lake.
According to the meteorological data recorded by an automatic meteorological station in Altun Mountain National Nature Reserve, the characteristics of summer and winter meteorological conditions are analyzed. It is found that the Altun Mountain National Nature Reserve is one low-temperature center in the central Xinjiang. The air temperature averaged in winter is -14.0 ℃, about 10.0 ℃ lower than that in Hotan and 6-8 ℃ lower than that in the similar latitude areas such as Yining and Hami. The mean air temperature in summer is 9.0 ℃, 15 ℃ lower than that in surrounding areas generally. Instantaneous wind speed averaged in summer is 3.6 m·s-1, higher than that in the winter, 2.4 m·s-1. Precipitation is high to 300 mm·a-1, mainly concentrated in summer, showing a characteristic of warm-rain over the same period.
In this paper, the experiment parameters of the geogrid reinforced clay embankment after freezing and thawing cycles were used to make a finite element analysis on various size models to determine the influence of the initial factors on the working performance of the reinforced clay structure. The finite element software ABAQUS was used to calculate the displacement and stress under the conditions of all kinds of calculation and the maximum of displacement and stress were gained. It is found that increase in reinforced geogrids within clay embankment can reduce vertical and horizontal displacements and the maximum shearing stress after freezing and thawing cycles, with the influence on soil's deformation stronger than on soil's shear stress; increase in soil's compaction degree can reduce the vertical and horizontal displacement of reinforced embankment and increase soil's shear stress; decrease in soil's initial moisture content can reduce the vertical and horizontal displacement of reinforced embankment and decrease soil's shear stress.
In this paper, the change of land use and landscape pattern, along with the changing reasons, in the Kaxgar River basin from 1990 to 2010 are analyzed, based on Landsat-TM and CBERS images in 1990, 2000 and 2010, combined with GIS technology. It is revealed that (1) the land use in the basin had changed significantly from 1990 to 2010, for example, cultivated land, construction land, saline, naked land, wetland and other unused land had increased, with the changing rates of 73.92%, 51.44%, 24.27%, 6.47%, 10.24% and 2.98%, respectively; the woodland, grassland, and sandy land had decreased, with the changing rates of -4.13%, -17.16% and -0.73%; the area of bare gravel had basically unchanged; (2) in the 20 years, 16.46% of the grassland and 3.36% of the woodland transferred into cultivated land; 0.18% of the grassland shifted into water wetland; 0.28% of the grassland shifted into saline land; (3) during this period, the cultivated land and water wetland had concentrated and gradually become dominant landscape types; the woodland and grassland had reduced and the fragmentation had also reduced, landscape dominance had decreased, landscape shape had become simple; (4) there were multiple effects on land use and landscape index in the Kaxgar River basin, such as growing population, economic interests, policy and technology factors, resulting in cultivated land expanding with some hidden dangers to the region ecological environment security, so rational use of water resources is very important for watershed ecological environment security.
Researches on soil CO2 fluxes in alpine meadow of permafrost regions could facilitate accurate estimation of annual total fluxes of the soil CO2 in the Tibetan Plateau. It is also of great significance to reveal soil carbon cycles and its response to global climate change in the plateau. An alpine meadow site in the permafrost region of the upper reaches of the Shule River in the northeast margin of the Tibetan Plateau was selected as a study area, and soil CO2 fluxes were regularly measured using static chamber/gas chromatogram method and LI-8100 automatic soil CO2 flux system. Combined with environmental factors (included soil temperature, soil moisture, soil salinity, air temperature, relative humidity and solar radiation), the emission characteristics of soil CO2 and the main influence factors were investigated. The results show that the alpine meadow soils were atmospheric CO2 sources during the whole observation periods, with the soil CO2 diurnal flux rate ranging from 2.52 to 532.81 mg·m-2·h-1. The annual total emission of soil CO2 was 1 429.88 g·m-2, with annual mean fluxes of 163.23 mg·m-2·h-1. The soil CO2 flux had significant correlation with air temperature and relative humidity, soil temperature, water content and salt content at the depth of 2 cm, 10 cm, 20 cm and 30 cm. The soil temperature at the depth of 2 cm, air temperature, solar radiation and soil salt content at the depth of 2 cm were the most important influence factors for soil CO2 flux during the completely thawed period, freezing process, completely frozen period and thawing processes, respectively. The 72.0%, 82.0% and 38.0% changes of soil CO2 flux variation can be explained with the best fitting temperature factor variation in the completely thawed period, freezing process and whole observation period, corresponding to 1.93, 6.62 and 2.09 of Q10 value, respectively. The results also show that the cumulative soil CO2 flux during freezing-thawing periods (including thawing and freezing periods) and completely frozen period accounts for 15.35% and 11.04% of the annual total emission, which should not be neglected in estimation of the soil CO2 flux in the alpine meadow of permafrost regions in the Tibetan Plateau.
