Local modeling of instability onset for global finger evolution     

《Advances in water resources》2014

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Flow regime shifts in the Little Piney creek (US)     

《Advances in water resources》2014

Non-stationarity of climate drivers and soil-use strongly affects the hydrologic cycle, producing significant inter-annual and multi-decadal fluctuations of river flow regimes. Understanding the temporal trajectories of hydrologic regimes is a key issue for the management of freshwater ecosystems and the security of human water uses. Here, long-term changes in the seasonal flow regime of the Little Piney creek (US) are analyzed with the aid of a stochastic mechanistic approach that expresses analytically the streamflow distribution in terms of a few measurable hydroclimatic parameters, providing a basis for assessing the impact of climate and landscape modifications on water resources. Mean rainfall and streamflow rates exhibit a pronounced inter-annual variability across the last century, though in the absence of clear sustained drifts. Long-term modifications of streamflow regimes across different periods of 2 and 8 years are likewise significant. The stochastic model is able to reasonably reproduce the observed 2-years and 8-years regimes in the Little Piney creek, as well as the corresponding inter-annual variations of streamflow probability density. The study evidences that a flow regime shift occurred in the Little Piney creek during the last century, with erratic regimes typical of the 30s/40s that had been progressively replaced by persistent flow regimes featured by more dumped streamflow fluctuations. Causal drivers of regime shift are identified as the increase of the frequency of events (a byproduct of climate variability) and the decrease of recession rates (induced by a decrease of cultivated lands). The approach developed offers an objective basis for the analysis and prediction of the impact of climate/landscape change on water resources.  相似文献   

Evapotranspiration and canopy characteristics of two lodgepole pine stands following mountain pine beetle attack   总被引：1，自引：0，他引：1       下载免费PDF全文

Mathew G. Brown  T. Andrew Black  Zoran Nesic  Vanessa N. Foord  David L. Spittlehouse  Arthur L. Fredeen  Rebecca Bowler  Nicholas J. Grant  Philip J. Burton  J. A. Trofymow  Dominic Lessard  Gesa Meyer 《水文研究》2014,28(8):3326-3340

Over the past decade, British Columbia (BC), has experienced the largest mountain pine beetle (MPB) outbreak on record. This study used the eddy‐covariance (EC) technique to examine the impact of the MPB attack on evapotranspiration (E) and associated canopy characteristics of two lodgepole pine stands with secondary structure (trees, saplings and seedlings surviving the attack) located in central BC. MPB‐06, an 85‐year‐old almost pure stand of pine trees, was first attacked in 2006, and by 2010, ~80% of the trees had been killed. MPB‐03, a 110‐year‐old stand with an overstory consisting of over 90% pine and a developed sub‐canopy, was first attacked in 2003 and by 2007 had > 95% pine canopy mortality. EC measurements began in August 2006 at MPB‐06 and in March 2007 at MPB‐03, and continued for four years. Annual total E ranged from 226 mm to 237 mm at MPB‐06, and from 280 to 297 mm at MPB‐03, showing relatively little year‐to‐year change at both sites over the four years. Increased E from the accelerated growth of the surviving vegetation (secondary structure, shrubs and herbs) compensated for reduction in E due to the death of the overstory. Monthly average daytime canopy conductance, the Priestley–Taylor (α), and the canopy–atmosphere decoupling coefficient (Ω) steadily increased during the growing season reaching approximate maximum values of 5 mm s^?1, 0.75 and 0.12, respectively. Potential evapotranspiration was approximated using a vapour pressure deficit‐dependent α obtained at high soil water content. Calculated water deficits indicated some water‐supply limitation to the surviving trees and understory at both sites. Rates of root zone drainage during the growing season were low relative to precipitation. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The dynamic response of fluid-saturated porous materials with application to seismically induced soil liquefaction     

《Soil Dynamics and Earthquake Engineering》2014

The numerical simulation of liquefaction phenomena in fluid-saturated porous materials within a continuum-mechanical framework is the aim of this contribution. This is achieved by exploiting the Theory of Porous Media (TPM) together with thermodynamically consistent elasto-viscoplastic constitutive laws. Additionally, the Finite Element Method (FEM) besides monolithic time-stepping schemes is used for the numerical treatment of the arising coupled multi-field problem. Within an isothermal and geometrically linear framework, the focus is on fully saturated biphasic materials with incompressible and immiscible phases. Thus, one is concerned with the class of volumetrically coupled problems involving a potentially strong coupling of the solid and fluid momentum balance equations and the algebraic incompressibility constraint. Applying the suggested material model, two important liquefaction-related incidents in porous media dynamics, namely the flow liquefaction and the cyclic mobility, are addressed, and a seismic soil–structure interaction problem to reveal the aforementioned two behaviors in saturated soils is introduced.  相似文献   

周至井数字化资料映震效能分析与研究     

彭玉柱  张世民  李建章 《震灾防御技术》2014,9(S1):718-725

地震台站观测人员清理自己的观测资料对促进地震观测资料在地震预报实践中的应用具有十分重要的意义。我们对周至井十多年的地下流体数字化观测资料进行了系统的整理,从固体潮特征、降雨特征、气压效应、同震变化与震前异常等方面进行了分析,初步结果认为周至井是一口很好的地震地下流体观测井孔,只要能对其观测数据出现的各种不正常现象加以分析,就有可能对未来将要发生的中强地震做出有一定价值的预报意见。  相似文献   

基于熵权物元可拓模型的冻土路基热稳定性评价   总被引：1，自引：0，他引：1  

阮国锋  张建明  穆彦虎  张虎  柴明堂 《冰川冻土》2014,36(1):123-129

冻土路基热稳定性评价是一个复杂的工程评价问题.应用可拓理论,选取年平均地温、体积含冰量、天然上限、路基高度及路基走向5个影响路基热稳定性的主要因素作为冻土路基热稳定性的评价指标,将熵权法引入可拓学理论中,避免确定指标权重的主观随意性,从而建立熵权物元可拓模型,并将该模型应用于青藏铁路普通路基的热稳定性评价.将评价结果与青藏铁路现场监测系统中4个普通路基断面热稳定性监测结果进行对比,结果表明应用物元可拓模型可以得到比较可靠的路基热稳定性评价结果.因此,该评价方法可应用于冻土路基热稳定性评价.  相似文献   

隧道仰坡地震动力响应特性振动台模型试验研究   总被引：2，自引：0，他引：2  

吴冬  高波  申玉生  周佳媚 《岩土力学》2014,35(7):1921-1928

为研究地震作用下山岭隧道仰坡的动力响应特性及仰坡坡体和衬砌结构的相互作用,设计并完成了隧道洞口段大型振动台模型试验。试验结果表明,地震作用下仰坡的加速度反应存在显著的非线性放大效应和趋表效应;当输入地震波幅值超过0.6g时,土体的非线性反应明显增强,加速度放大系数显著降低,表现出放大效应饱和的特性,且沿坡体竖直向上,加速度分布逐渐表现出平均化的趋势;隧道洞口段仰坡水平向动力反应受隧道结构存在的影响较小,可简化为自然边坡进行分析;仰坡的动力失稳是影响衬砌结构安全性的重要因素,当输入地震波幅值较小时,竖直向地震作用下衬砌主要受力部位受力要大于水平向地震作用,当幅值较大时,水平向地震动对衬砌结构的影响则明显大于竖向地震动;均质仰坡的破坏部位主要位于仰坡坡肩至坡面上部,破坏过程表现为地震力诱发-坡肩土体拉裂张开-坡肩土体倾倒崩塌-崩塌的土体沿坡面滑落碰撞-形成碎屑流堆积于坡脚。模型试验的结果能为山岭隧道洞口段的理论分析、计算和设计提供指导和依据。  相似文献   

山岳型旅游地水资源系统安全评价——以黄山风景区为例   总被引：2，自引：1，他引：1  

王群  陆林  杨兴柱 《地理研究》2014,33(6):1059-1072

以黄山风景区为案例地,基于1998-2012 年15 年间的水资源与旅游发展相关数据,运用集对分析法,从扰动性和应对能力两个层面建立评价指标体系,对其年际及月际水资源系统安全态势进行评价。结果表明：① 15 年间,黄山风景区年际水资源系统安全性综合指数总体处于中等水平,并呈现逐年上升趋势;② 月际水资源系统安全性平均指数虽总体也处于中等水平,但存在月际差异,大体呈“双峰双谷”型;③ 年际系统安全性与扰动性指数、应对能力指数呈现出显著的正相关关系。月际系统安全性则与扰动性指数、应对能力指数呈现出负相关关系。应对能力强弱对年际水资源安全性具有重要作用,对月际系统安全性调节具有局限性。④ 水资源潜力、旅游发展、用水效率和纳污能力共同构成了系统安全的扰动要素,资金收入与投入、技术与道德措施形成了系统的应对能力,但各因子作用强度、性质不同。  相似文献   

2011年春末夏初长江中下游地区旱涝急转成因初探   总被引：23，自引：9，他引：14  

封国林  杨涵洧  张世轩  王阔  沈柏竹 《大气科学》2012,36(5):1009-1026

选用NCEP/NCAR、NOAA、国家气候中心(NCC)提供的各要素资料及NOAA-Hysplit模型,对2011年春末夏初发生在中国长江中下游地区旱涝急转的降水异常事件及其影响机制进行初步分析,并建立天气学概念模型.结果表明:(1)长江中下游地区,尤其是(27°N～～32°N,l10°E～120°E)区域在6月第1候...  相似文献   

1999—2008年夏季华北冷涡的异常特征     

郁珍艳  何立富  李泽椿 《气象科技》2012,40(2):256-261

利用1999—2008年5—8月中国160站月平均气温资料、每日2次的MICAPS资料及每日4次的NCEP 1°×1°资料,通过定义一个夏季华北冷涡强度指数(NCCVI),研究了夏季华北冷涡异常年西太平洋副高、东亚季风、高空急流及低层垂直运动的异常特征。结果表明：夏季NCCVI异常强年500 hPa上贝加尔湖地区有气旋性环流发展,从贝加尔湖至我国华北地区为一显著的高空槽所控制,冷空气较活跃并随槽后引导气流扩散南下影响华北地区。对流层各层偏暖湿,200 hPa上高空急流偏强,700 hPa上高纬冷涡后部偏北气流加强,低纬偏南气流加强,冷暖空气在华北交汇,华北和东北地区低层上升运动发展。同期副热带高压偏强,位置略偏南;东亚夏季风偏强, 加强了水汽输送。夏季NCCVI异常弱年相反。  相似文献