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Annual natural runoff is an important index of a river, which may be affected by solar activities. In this study, 304 years of annual natural runoff at the Sanmenxia station located in the Yellow River and the sunspot relative number are decomposed with the application of a Complex Morlet. According to the results of real part, modulus and second power of modulus, the annual runoff series at the Sanmenxia station has an obvious periodic oscillation on 90–100, 50–80, 35–50, 15–35, about 10, and less than 10-year scales. Also, there are obvious periodic variability with 60–90 years, 30–50 years and about 10 years. There are two centers of energy: one is about 1840–1850 on 7–11-year scale and the other is about 1825–1925 on 60–70-year scale. From the wavelet variance, 3, 26, 46, 68 year periods are detected within a 100-year scale, and the 68-year period is the most significant. Similar analyses are conducted for the sunspot relative number within the same period 1700–2003. The sunspot series shows 11- and 60-year period variation, as well as eight energy centers. Then, the correlation analyses for 11- and 60-year serial scales are computed. From a long-term period (1700–2003) view, there is no notable correlation between the natural runoff and the sunspot relative number; however, it is evident that the correlations exist within a short-term period. The results also indicate that the relationships between solar activities and the natural runoff in the Yellow River are complicated. 相似文献
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采用1992年7月—2008年2月黄河干流潼关、三门峡、小浪底等水质监测断面氨氮逐月浓度监测数据,分析了小浪底水库运行前后潼关、三门峡、小浪底的氨氮年通量、年平均浓度变化情况,并结合潼关自动站与花园口自动站氨氮监测数据以及断面过水流量历史记录,研究了小浪底水库对氨氮的水环境效应。结果表明:小浪底水库运行后,就氨氮指标而言,小浪底坝下断面水质达标率大幅提高;从氨氮浓度波峰出现时间来看,小浪底断面氨氮浓度变化比潼关、三门峡断面滞后,滞后时间为30~60 d;小浪底水库下泄流量越大,有效库容越小,水库对氨氮的稀释作用越小,氨氮波峰滞后时间越短。 相似文献
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水沙变异对黄河三角洲湿地面积演变的影响 总被引:2,自引:0,他引:2
水沙过程是塑造湿地生态系统结构与功能的重要驱动力,控制着湿地的形成与演化。利用1976年-2014年近40年黄河三角洲湿地面积变化的遥感影像数据,系统分析湿地面积、湿地重心和南北区域湿地类型的动态变化进特征。研究结果显示:近40年来黄河三角洲人工湿地面积增加约1 000倍,自然湿地面积呈波动下降趋势,减少约41.9%;芦苇、滩涂、养殖及盐田湿地等典型湿地面积重心整体由西北向东南方向位移;南北部区域的湿地类型的演变出现呈现较为明显的差异特征,其中北部芦苇湿地、滩涂湿地面积呈减少趋势,南部芦苇湿地面积整体呈增加趋势,滩涂湿地面积先增加后减少。研究结果可为水沙变异条件下黄河三角洲湿地生态系统的保护与修复提供科学依据。 相似文献
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《Computer Methods in Applied Mechanics and Engineering》2005,194(36-38):3771-3796
The objective of the paper is to set forth, in a consistent manner, reasons for the appearance of excessive energy in the four-noded membrane quadrilateral element and to propose a formulation leading to simple and reliable elements that are less sensitive to distortions of the geometrical shape. By presenting the differential geometry, emphasis is placed upon those geometrical attributes which are inherently related to the quadrilateral. A modified version of the functional of Hu-Washizu is employed for the discretization. Appropriate approximations for the displacements/rotations are chosen and the physical meaning of the various parameters is identified. A systematic procedure is followed for the approximation of stress and strain. The convergence of the formulation is investigated by examining the inf–sup condition and applying the patch test. Also, results of numerical examples and comparisons with other elemental formulations are presented. 相似文献
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植被的变化特征是流域生态监测的重要内容和流域综合管理决策的基础信息。基于谷歌地球引擎(Google Earth Engine,GEE),利用空间分辨率为250 m的MODIS-EVI(Enhanced Vegetation Index)产品,研究2001~2017年黑河流域植被的时空变化趋势及延续性特征。结合气温、降水与河流径流量观测数据,分析黑河流域上游、中下游绿洲与非绿洲区植被变化的影响因素。结果表明:近17年来黑河流域植被年最大EVI值年均增幅为0.0039,年均新增植被面积为480.3 km^2。受气温、降水、耕地开垦、水资源管理措施及与其密切相关的地下水等因素的不同影响,上中下游表现出不同的变化特征。无论是年最大EVI值还是植被面积,中游的增加趋势最为显著,绿洲区较非绿洲区增加趋势更为明显。这种变化趋势短期内可能延续,但长时间内存在较大风险。研究为快速监测植被变化提供了示范,揭示了干旱区植被监测中长势变化与类型变化的同等重要性,流域植被变化的区域协同性对合理分水、加强地表-地下水协同管理等流域综合管理提出了更高要求。 相似文献
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为保护黄河三角洲湿地生态系统,掌握湿地变化趋势,以 1986—2018 年间 15 a 卫星遥感影像为数据源,通过 ERDAS 9.0 和 ArcGIS 10.3 平台开展黄河三角洲湿地遥感解译,建立土地利用转移矩阵,分析黄河三角洲湿地面积和分布格局及变化特征。结果显示:湿地是黄河三角洲主要生态系统类型,主要分布在沿海区域, 与 20 世纪 80 年代相比,黄河三角洲湿地面积整体下降,其中自然湿地萎缩严重,人工湿地增长迅速,湿地面积和结构均发生较显著变化,而区域土地资源开发是湿地结构变化的主要因素。研究成果表明:基于遥感解译,采用 ERDAS 9.0 和 ArcGIS 10.3 平台能快速获取较多湿地类型信息,提高提取精度,可为大范围土地利用分类研究提供方法参考。 相似文献
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Caihong Hu Xueli Zhang Changqing Li Chengshuai Liu Jinxing Wang Shengqi Jian 《Water Resources Management》2022,36(1):103-117
Water Resources Management - Floods are among the most dangerous disasters that affect human beings. Timely and accurate flood forecasting can effectively reduce losses to human life and property... 相似文献