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51.
Monthly sediment load and streamflow series spanning 1963–2004 from four hydrological stations situation in the main stem of the Yangtze River, China, are analysed using scanning t‐test and the simple two‐phase linear regression scheme. Results indicate significant changes in the sediment load and streamflow from the upper reach to the lower reach of the Yangtze River. Relatively consistent positive coherency relations can be detected between streamflow and sediment load in the upper reach and negative coherency in the middle and lower reaches. Interestingly, negative coherency is found mainly for larger time scales. Changes in sediment load are the result mainly of human influence; specifically, the construction of water reservoirs may be the major cause of negative coherency. Accentuating the human influence from the upper to the lower reach results in inconsistent correlations between sediment load and streamflow. Decreasing sediment load being observed in recent years has the potential to alter the topographical properties of the river channel and the consequent development and recession of the Yangtze Delta. Results of this study are of practical significance for river channel management and evaluation of the influence of human activities on the hydrological regimes of large rivers. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Using a double resonant KTiOPO4 (KTP) intracavity optical parametric oscillator operating at degenerated point of 2 μm, we demonstrate a unique mid-infrared source based on difference frequency generation in GaSe crystal. The output tuning range is 8.42-19.52 μm, and a peak power of 834 W for type-I phase matching scheme and 730 W for type-II phase matching scheme are achieved. Experimental results show that this oscillator is a good alternative to the generator of a compact and tabletop mid-infrared radiation with a widely tunable range. 相似文献
54.
On 1 December 2007, eight ‘Small Island Developing States’ in the Western and Central Pacific Ocean implemented a management regime restricting the total number of days fished by tuna purse seine vessels within their waters, commonly referred to as the Vessel Day Scheme (VDS). The VDS is seen as one component of management arrangements to reduce fishing mortality on bigeye and yellowfin tuna, constrain fishing effort, and increase the rate of return from access fees by Distant Water Fishing Nations. 相似文献
55.
黄河"八七"分水方案是流域水资源管理的重要依据。颁布30余年来,黄河流域自然环境、经济社会等发生了显著变化,亟需科学认识分水方案对环境变化扰动的适应性。运用动力系统原理构建分水方案适应性的动力微分方程和综合评价模型,从敏感性、稳定性、抗力和恢复力4个方面建立包含20个指标的适应性评价指标体系,定量评价1999年以来分水方案的适应性,并采用HP(Hodrick-Prescott)滤波识别适应性变化趋势。结果表明:分水方案对环境变化的适应性良好,19年中63.2%的年份适应性值大于1;适应性先升后降,2005年达到峰值,之后逐渐降低,2014年起适应性值小于1,表现为不适应。分析影响分水方案适应性的主要因素,提出分水方案调整策略,为支撑流域水资源管理提供方向参考。 相似文献
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本次需要治理的5处矿山遗留的地质环境问题严阻碍了社会发展,使当地人居环境恶化。综合地质灾害、生态环境、气象水文条件以及居民生产活动等因素,提出合理的治理工程方案,解决治理区内突出的矿山地质环境问题,消除或减少露采边坡存在的威胁,改善生态环境,营造一个宜居、宜人的生存环境,确保地方经济的可持续发展。通过治理消除或最大限度的减少露采边坡存在的威胁,确保人民生命财产安全和社会稳定。 相似文献
57.
Chenglong Ma Xiaodong Chen Liming Jiang Heping Sun Jianqiao Xu Jinglong Dong Dewei Li 《地球科学进展》2019,34(2):164-174
Based on the principle of InSAR (Interferometirc Synthetic Aperture Radar) characterized by large-scale, continuity, permanency and dynamic, we took vertical displacement of solid Earth tide as an example to simulate the large-scale deformation observed by lunar based InSAR for the first time in the study and the observation ability was analyzed. Solid Earth tide has a feature of a large-space distribution range and the lunar based InSAR exhibits a feature of an ultra-wide swath imaging. According to these features, a simplified observation geometry model was established and a mid-low latitudes area with 50 degrees span in both longitude and latitude was selected as the simulation area. Then the revisit time intervals of the lunar based SAR for the selected area and the tidal vertical displacements at the points scanned by the radar were calculated. The time differentials were further computed to get the relative vertical deformation of the solid Earth tide. The simulation results show that the revisit period of the lunar based radar is about 24.8 hours and the maximum vertical displacement in 30 days is up to 30 cm. Since the designed accuracy of the lunar based InSAR reaches several centimeters, the observing of the vertical displacement of the solid Earth tide by using the lunar based InSAR is feasible in theory as the maximum magnitude of the vertical displacement is 1 order of magnitude larger than the designed accuracy. Theoretically ,solid Earth tide is observable by using lunar based InSAR in a sizable area.We can also use the observation data to study the temporal and spatial variation characteristics when observation time lasts two revisit periods or more. On the other hand,the result of the study also provides references for the parameter designing of other observations using the lunar based InSAR, especially for observing large-scale geodynamic phenomena. 相似文献
58.
对滇西实验场1992年以来地下流体前兆观测资料进行分析研究,选取应震效果通过R信度检验(对应MS≥5.0级地震)的8条单项前兆指标。综合考虑单项前兆指标虚报率和漏报率对指标信度的影响,对单项前兆指标利用数学模型进行综合处理,减少了虚报和漏报的次数,预测效果明显提高。利用分级预警模式分别建立了中期(T≤6个月)和短临(T≤3个月)预测模型。综合预测方案还提供了地点判定原则和震级估算原则。最终提供地震短临预测三要素。运用本综合预测方案对2011年腾冲5级双震、2013年洱源5级双震和德钦两次5级地震作用了较为成功的短临预测。 相似文献
59.
An improved diagnostic stratocumulus scheme based on estimated inversion strength and its performance in GAMIL2 总被引:1,自引:0,他引:1
Based on satellite data and the estimated inversion strength (EIS) derived by Wood et al. (2006), a feasible and uncomplicated stratocumulus scheme is proposed, referred to as EIS scheme. It improves simulation of cloud radiative forcing (CRF) in the Grid-point Atmospheric Model of IAP/LASG version 2 (GAMIL2.0) model. When compared with the original lower troposphere stability (LTS) scheme, the EIS scheme reproduces more reasonable climatology distributions of clouds and CRF. The parameterization partly corrects CRF underestimation at mid and high latitudes and overestimation in the convective region. Such improvements are achieved by neglecting the effect of free-tropospheric stratification changes that follow a cooler moist adiabat at middle and high latitude, thereby improving simulated cloudiness. The EIS scheme also improves simulation of the CRF interannual variability. The positive net CRF and negative stratiform anomaly in the East Asian and western North Pacific monsoon regions (EAWNPMR) are well simulated. The EIS scheme is more sensitive to sea surface temperature anomalies (SSTA) than the LTS. Therefore, under the effect of a warmer SSTA in the EAWNPMR, the EIS generates a stronger negative stratiform response, which reduces radiative heating in the low and mid troposphere, in turn producing strong subsidence and negative anomalies of both moisture and cloudiness. Consequent decreases in cloud reflection and shading effects ultimately improve simulation of incoming surface shortwave radiative fluxes and CRF. Because of the stronger subsidence, a stronger anomalous anticyclone over the Philippines Sea is simulated by the EIS run, which leads to a better positive precipitation anomaly in eastern China during ENSO winter. 相似文献
60.