The unfrozen water content and ice content of frozen soil change continuously with varying temperatures, resulting in the temperature dependence of mechanical properties of frozen soil. Thus the dynamic behavior of embankment in permafrost regions under train loading also alters with seasons. Based on a series of strong-motion tests that were carried out on the traditional embankment of Qinghai-Tibet Railway (QTR) in permafrost regions, the acceleration waveforms recorded at the embankment shoulder and slope toes were obtained. Testing results show an obvious attenuation effect on the vertical train loading from road shoulder to slope toes. Furthermore, numerical simulations of a traditional embankment under vertical train loading in different seasons were conducted, and the dynamic behavior of the embankment was described. The results show that the vibration attenuation in the cold season is greater than that in the warm season. The maximum acceleration of vibration drops to about 5% when the train vibration load is transferred through the embankment into the permafrost, and the high-frequency components are absorbed when the vibration transmits downward. Moreover, the dynamic stress under the dynamic train loading decreases exponentially with an increasing depth in different seasons. The results can be a reference for design and maintenance of embankments in permafrost regions.
Determining an optimal sample size is a key step in designing field surveys, and is particularly important for detecting the spatial pattern of highly variable properties such as soil organic carbon (SOC). Based on 550 soil sampling points in the near-surface layer (0 to 20 cm) in a representative region of northern China’s agro-pastoral ecotone, we studied effects of four interpolation methods such as ordinary kriging (OK), universal kriging (UK), inverse distance weighting (IDW) and radial basis function (RBF) and random subsampling (50, 100, 200, 300, 400, and 500) on the prediction accuracy of SOC estimation. When the Shannon's Diversity Index (SHDI) and Shannon's Evenness Index (SHEI) was 2.01 and 0.67, the OK method appeared to be a superior method, which had the smallest root mean square error (RMSE) and the mean error (ME) nearest to zero. On the contrary, the UK method performed poorly for the interpolation of SOC in the present study. The sample size of 200 had the most accurate prediction; 50 sampling points produced the worst prediction accuracy. Thus, we used 200 samples to estimate the study area's soil organic carbon density (SOCD) by the OK method. The total SOC storage to a depth of 20 cm in the study area was 117.94 Mt, and its mean SOCD was 2.40 kg/m2. The SOCD kg/(C?m2) of different land use types were in the following order: woodland (3.29) > grassland (2.35) > cropland (2.19) > sandy land (1.55).
Water consumption is a key role in improving the efficiency and sustainability of water management in arid environments. In this study, we explored an approach based on meta-analysis, MODIS NDVI products, land-use spatial distribution, and soil water physical parameters to gain insight into long-term and large scale distribution of land use and water consumption, maintain maximum Zhangye Oasis area according to Heihe River runoff, and suitable water resource management in Zhangye Oasis. This approach was initiated in order to improve the efficiency of irrigation and water resource management in arid regions Results showed that Heihe River runoff can maintain a maximum Zhangye Oasis area of 22.49×104 hm2. During the 2000-2016 growing seasons, actual oasis water consumption ranged from 11.35×108 m3 to 13.73×108 m3, with a mean of (12.89 ± 0.60)×108 m3; if maintaining agricultural production and oasis stability was chosen, oasis water consumption ranged from 10.24×108 m3 to 12.37×108 m3, with a mean of (11.62 ± 0.53)×108 m3. From the perspective of water resources management and ecosystem stability, it is necessary to reduce the area of Zhangye Oasis or choose the minimum water consumption method to manage the oasis, to ease the pressure of water shortage and maintain stable and sustainable development of the Zhangye Oasis. These results can provide future practical guidance for water resource management of coordinated development of the economy and the environment in an arid area.
Saltation bombardment is a dominate dust emission mechanism in wind erosion. For loose surfaces, splash entrainment has been well understood theoretically. However, the mass loss predictions of cohesive soils are generally empirical in most wind erosion models. In this study, the soil particle detachment of a bare, smooth, dry, and uncrusted soil surface caused by saltation bombardment is modeled by means of classical mechanics. It is shown that detachment rate can be analytically expressed in terms of the kinetic energy or mass flux of saltating grains and several common mechanical parameters of soils, including Poisson's ratio, Young's modulus, cohesion and friction angle. The novel expressions can describe dust emission rate from cohesive surfaces and are helpful to quantify the anti-erodibility of soil. It is proposed that the mechanical properties of soils should be appropriately included in physically-based wind erosion models.
The Taklimakan Desert, the world's second largest desert, plays an important role in regional climate change. Previous studies on its spatial temperature features suffered from sparse conventional detection data, but the Atmospheric Infrared Sounder (AIRS) provides excellent temperature retrievals with high spatiotemporal resolution. Validation of AIRS temperature retrievals over desert regions with high land-surface emissivity, the key contributor to inversion error, is essential before using these data in regional weather/climate modeling. This paper examines the correlation coefficients, root mean square error (RMSE) and mean BIAS between AIRS-retrieved atmospheric temperature data and radiosonde observations (RAOBs) in the Taklimakan Desert hinterland and oases in the morning and at dusk. Firstly, the AIRS retrievals are consistent with RAOBs and are more consistent in the morning than at dusk. The consistency is better over a small-scale desert oasis than over a large-scale oasis in the morning and exhibits the opposite trend at dusk. The correlation coefficient over the hinterland is high in the morning but negative at dusk due to high desert-surface emissivity. Second, the RMSEs, which are all smaller than 3 K, are generally higher over desert sites than over oasis sites and slightly lower over a small-scale oasis than over a large-scale oasis in the morning. At dusk, the RMSEs are higher over desert sites than over oases and slightly higher over a small-scale oasis than over a large-scale oasis. Furthermore, the RMSEs are generally higher in the morning than at dusk over a large-scale oasis and lower in the morning than at dusk over a small-scale oasis. Third, the absolute mean BIAS values are mostly lower than 1 K. In the morning, relative to RAOB temperatures, the retrieval temperatures are higher over desert sites but lower over oasis sites. At dusk, the retrieval temperatures are lower than RAOB temperatures over both desert and oasis sites. The retrieval temperatures are higher than RAOB temperatures over desert sites in the morning but slightly lower at dusk. Most absolute mean BIAS values are higher in the morning than at dusk over both oasis and desert sites. Finally, the consistency between the AIRS and RAOB temperature data is high from 700 hPa to 100 hPa in the morning and from 700 hPa to 300 hPa at dusk. The difference between the AIRS and RAOB temperature data is generally higher in the morning than that at dusk. The RMSE differences between the AIRS and RAOB data are slightly lower in the morning than at dusk and are lower in the middle layers between 700 hPa and 150 hPa than in the layers above 150 hPa during both the morning and night. The BIAS is lower in the morning than at dusk below 300 hPa but higher in the upper layers. Moreover, the BIAS value is positive in the middle layers between 500 hPa and 150 hPa and negative at other levels at both times. Generally, the AIRS retrieval temperatures are reliable and can be used in further studies in the Taklimakan Desert.
Based on monthly evaporation of two meteorological stations in the Gulang River Basin of China, the inter-annual variation of evaporation during 1959-2013 were analyzed using Mann-Kendall and wavelet analysis. The results demonstrated that the annual evaporation show a fluctuating increase over the past 50 years approximately, with an average increase rate of 4.26 mm per decade. The overall trend was decrease-increase-decrease. According to the cumulative anomaly curve, the turning point of the annual evaporation occurred in 1979, in which the evaporation increased in the early stage and decreased in the later stage. Meanwhile, the seasonal variation of the evaporation shows that it decreased in Spring and Autumn, and increased in Summer and Winter, especially obvious for the later. The evaporation abruptly changed in Spring and Summer in 2008 and in Winter in 1994. In addition, all evaporation increased after the changes. However, the evaporation in Autumn abruptly changed in 1986 and 1999, which show a trend of increase-decrease-increase. Wavelet analysis shows that evaporation in Summer and wet season would decrease in the next few years, and in the other seasons would increase. Based on the aforementioned analysis, it can be concluded that increased evaporation is mainly induced by increase of evaporation in dry season, especially in Winter, and this trend to be continued in the future for the Gulang River Basin.
