分类： 地球科学 >> 地理学 分类： 交通运输工程 >> 道路工程 提交时间： 2019-03-31
摘要： 基于超制图学的思想，建立模型将乘坐轻轨的时间距离换算成以米（m）为单位的空间距离。在此基础上,通过地理信息系统（GIS）的地图投影空间变换方法,用换算出的距离重新定义两地间距离,变形原地图形成时间距离地图。将时间距离空间化，利用技术手段，对时间距离进行可视化表达。结果发现，轻轨对于城市形态的影响受到站点离所选取的中心点距离的影响，呈现离中心点越远变形越大；离中心点越近变形越小。轻轨对商业中心布局的影响基本呈现圈层分布。时间距离压缩了传统城市形态。随着乌鲁木齐地铁建设进程的推进和基础设施的完善,城市内部进一步压缩时间距离仍有很大余地，已有商业中心应进行升级。本研究为乌鲁木齐城市建设提供一种新的参考与思路。
分类： 地球科学 >> 地理学 提交时间： 2019-03-28 合作期刊: 《干旱区科学》
摘要： Soil water is an important composition of water recycle in the soil-plant-atmosphere continuum. However, intense water exchange between soil-plant and soil-atmosphere interfaces only occurs in a certain layer of the soil profile. For deep insight into water active layer (WAL, defined as the soil layer with a coefficient of variation in soil water content >10% in a given time domain) in the Loess Plateau of China, we measured soil water content (SWC) in the 0.0–5.0 m soil profile from 86 sampling sites along an approximately 860-km long south-north transect during the period 2013–2016. Moreover, a dataset contained four climatic factors (mean annual precipitation, mean annual evaporation, annual mean temperature and mean annual dryness index) and five local factors (altitude, slope gradient, land use, clay content and soil organic carbon) of each sampling site was obtained. In this study, three WAL indices (WAL-T (the thickness of WAL), WAL-CV (the mean coefficient of variation in SWC within WAL) and WAL-SWC (the mean SWC within WAL)) were used to evaluate the characteristics of WAL. The results showed that with increasing latitude, WAL-T and WAL-CV increased firstly and then decreased. WAL-SWC showed an opposite distribution pattern along the south-north transect compared with WAL-T and WAL-CV. Average WAL-T of the transect was 2.0 m, suggesting intense soil water exchange in the 0.0–2.0 m soil layer in the study area. Soil water exchange was deeper and more intense in the middle region than in the southern and northern regions, with the values of WAL-CV and WAL-T being 27.3% and 4.3 m in the middle region, respectively. Both climatic (10.1%) and local (4.9%) factors influenced the indices of WAL, with climatic factors having a more dominant effect. Compared with multiple linear regressions, pedotransfer functions (PTFs) from artificial neural network can better estimate the WAL indices. PTFs developed by artificial neural network respectively explained 86%, 81% and 64% of the total variations in WAL-T, WAL-SWC and WAL-CV. Knowledge of WAL is crucial for understanding the regional water budget and evaluating the stable soil water reserve, regional water characteristics and eco-hydrological processes in the Loess Plateau of China.
分类： 地球科学 >> 地球化学 提交时间： 2019-03-28 合作期刊: 《干旱区科学》
摘要： The Alagxa Plateau, in the margin of the northeastern Tibetan Plateau, is one of the most important dust source areas in East Asia, and the widespread sandy desert in the area is important both as a reservoir and a source of eolian silty. The northeastern margin of the Tibetan Plateau is one of the most actively-growing mountain belt on earth, and has large amounts of debris, with masses of fine grained material, which were continuously mobilized and deposited in the Alagxa Plateau by rivers, forming broad alluvial fans. It is possible that the role of fluvial sediments as a source of silty dust in the Alagxa Plateau has been underestimated. In this study, we test this hypothesis by investigating the iron mineralogical and geochemical characteristics of the fluvial sediments and the surface material of the sandy desert in the Alagxa Plateau, and comparing them with paleo-eolian dust deposits (loess) in the adjacent Chinese Loess Plateau (CLP) to investigate the possible linkages among the fluvial sediments, sandy desert and the last glacial loess of the CLP. The results show that sandy desert typically have high contents of goethite, and high ratios of goethite to hematite, similar to the fluvial sediments in the Alagxa Plateau. Based on the major element characteristics, field investigations and the results of previous studies, we found a genetic link between the silt component of the fluvial sediments and the sandy desert in the Alagxa Plateau with high value of Gt (goethite) and similarity of the Gt/(Hm (hematite)+Gt) ratio. But the silt component of the sandy desert main come from the adjacent fluvial sediments. The iron mineralogical characteristics (magnetic susceptibility, ARM (anhysteretic susceptibility), SIRM (saturation isothermal remanent magnetization) and SIRMAF100mT (SIRM demagnetized at 100 mT)) of the CLP samples overlap with those of the fluvial sediments in the Alagxa Plateau, but there is a mismatch with the sandy desert samples. This suggests that the fluvial sediments are the source of a large amount of silty material which could be transported to the CLP. Therefore, we conclude that the fluvial sediment in the Alagxa Plateau is an important source of eolian silt, which is deposited in downwind region, and that this source has been previously underestimated.
分类： 地球科学 >> 地理学 提交时间： 2019-03-28 合作期刊: 《干旱区科学》
摘要： Complex erosion by wind and water causes serious harm in arid and semi-arid regions. The interaction mechanisms between water erosion and wind erosion is the key to further our understanding of the complex erosion. Therefore, in-depth understandings of the influences of water erosion on wind erosion is needed. This research used a wind tunnel and two rainfall simulators to investigate the influences of water erosion on succeeding wind erosion. The wind erosion measurements before and after water erosion were run on semi-fixed aeolian sandy soil configured with three slopes (5°, 10° and 15°), six wind speeds (0, 9, 11, 13, 15 and 20 m/s), and five rainfall intensities (0, 30, 45, 60 and 75 mm/h). Results showed that water erosion generally restrained the succeeding wind erosion. At a same slope, the restraining effects decreased as rainfall intensity increased, which decreased from 70.63% to 50.20% with rainfall intensity increased from 30 to 75 mm/h. Rills shaped by water erosion could weaken the restraining effects at wind speed exceeding 15 m/s mainly by cutting through the fine grain layer, exposing the sand layer prone to wind erosion to airflow. In addition, the restraining effects varied greatly among different soil types. The restraining effects of rainfall on the succeeding wind erosion depend on the formation of a coarsening layer with a crust and a compact fine grain layer after rainfall. The findings can deepen the understanding of the complex erosion and provide scientific basis for regional soil and water conservation in arid and semi-arid regions.
分类： 地球科学 >> 地理学 提交时间： 2019-03-28 合作期刊: 《干旱区科学》
摘要： An abrupt temperature change and a warming hiatus have strongly influenced the global climate. This study focused on these changes in Inner Mongolia, China. This study used the central clustering method, Mann-Kendall mutation test and other methods to explore the abrupt temperature change and warming hiatus in three different temperature zones of the study region based on average annual data series. Among the temperature metrics investigated, average minimum temperature (Tnav) shifted the earliest, followed by average temperature (Tnv) and average maximum temperature (Txav). The latest change was observed in summer (1990s), whereas the earliest was observed in winter (1970s). Before and after the abrupt temperature change, Tnav fluctuated considerably, whereas there was only a slight change in Txav. Before and after the abrupt temperature change, the winter temperature changed more dramatically than the summer temperature. Before the abrupt temperature change, Tnav in the central region (0.322°C/10a) and west region (0.48°C/10a) contributed the most to the increasing temperatures. After the abrupt temperature change, Tnav in winter in the central region (0.519°C/10a) and in autumn in the west region (0.729°C/10a) contributed the most to the temperature increases. Overall, in the years in which temperature shifts occurred early, a warming hiatus also appeared early. The three temperature metrics in spring (1991) in the east region were the first to exhibit a warming hiatus. In the east region, Txav displayed the lowest rate of increase (0.412°C/a) in the period after the abrupt temperature change and before the warming hiatus, and the highest rate of increase after the warming hiatus.
分类： 地球科学 >> 地理学 提交时间： 2019-03-28 合作期刊: 《干旱区科学》
摘要： Drought acutely affects economic sectors, natural habitats and communities. Understanding the past spatial and temporal patterns of drought is crucial because it facilitates the forecasting of future drought occurrences and informs decision-making processes for possible adaptive measures. This is especially important in view of a changing climate. This study employed the World Meteorological Organization (WMO)-recommended standardized precipitation index (SPI) to investigate the spatial and temporal patterns of drought in Zambia from 1960 to 2016. The relationship between the occurrence of consecutive dry days (CDD; consecutive days with less than 1 mm of precipitation) and SPI was also investigated. Horizontal wind vectors at 850 hPa during the core of the rainy season (December–February) were examined to ascertain the patterns of flow during years of extreme and severe drought; and these were contrasted with the patterns of flow in 2007, which was a generally wet year. Pressure vertical velocity was also investigated. Based on the gamma distribution, SPI successfully categorized extremely dry (with a SPI value less than or equal to –2.0) years over Zambia as 1992 and 2015, a severely dry (–1.9 to –1.5) year as 1995, moderately dry (–1.4 to –1.0) years as 1972, 1980, 1987, 1999 and 2005, and 26 near normal years (–0.9 to 0.9). The occurrence of CDD was found to be strongly negatively correlated with SPI with a coefficient of –0.6. Further results suggest that, during wet years, Zambia is influenced by a clockwise circulating low-pressure zone over the south-eastern Angola, a second such zone over the northern and eastern parts, and a third over the Indian Ocean. In stark contrast, years of drought were characterized by an anti-clockwise circulating high-pressure zone over the south-western parts of Zambia, constraining precipitation activities over the country. Further, wet years were characterized by negative pressure vertical velocity anomalies, signifying ascending motion; while drought years were dominated by positive anomalies, signifying descending motion, which suppresses precipitation. These patterns can be used to forecast drought over Zambia and aid in strategic planning to limit the potential damage of drought.
分类： 地球科学 >> 水文学 提交时间： 2019-03-28 合作期刊: 《干旱区科学》
摘要： The increasing shortage in water resources is a key factor affecting sustainable socio-economic development in the arid region of Northwest China (ARNC). Water shortages also affect the stability of the region's oasis ecosystem. This paper summarizes the hydrological processes and water cycle of inland river basins in the ARNC, focusing on the following aspects: the spatial-temporal features of water resources (including air water vapor resources, runoff, and glacial meltwater) and their driving forces; the characteristics of streamflow composition in the inland river basins; the characteristics and main controlling factors of baseflow in the inland rivers; and anticipated future changes in hydrological processes and water resources. The results indicate that: (1) although the runoff in most inland rivers in the ARNC showed a significant increasing trend, both the glaciated area and glacial ice reserves have been reduced in the mountains; (2) snow melt and glacier melt are extremely important hydrological processes in the ARNC, especially in the Kunlun and Tianshan mountains; (3) baseflow in the inland rivers of the ARNC is the result of climate change and human activities, with the main driving factors being the reduction in forest area and the over-exploitation and utilization of groundwater in the river basins; and (4) the contradictions among water resources, ecology and economy will further increase in the future. The findings of this study might also help strengthen the ecological, economic and social sustainable development in the study region.
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