1961 - 2017年中国东北地区降雪时空演变特征分析

利用东北地区162个气象台站逐日降水量和天气现象数据, 采用统计分析方法, 对近57年（1961 - 2017年）降雪的气候特征和时空演变规律进行了分析。结果表明： 降雪量和降雪日数最多出现在12月, 小雪和中雪最多出现在11月或12月, 大雪和暴雪在冬末春初出现概率最高。降雪分布为山地大于平原, 平原地区自北向南、 自东向西减少, 降雪高值区主要位于大兴安岭北部、 小兴安岭和长白山区, 降雪强度中心位于长白山区和辽宁中部平原地区。年、 秋季、 冬季、 春季降雪量占同期降水量比例分别为4.7%、 7.0%、 84.4%和7.6%; 辽宁省西部山区和南部大连地区日最大降雪量占年总降雪量比例最高, 最长连续降雪日数在2 d以下, 降雪较高纬度地区更为集中。近57年降雪量和降雪强度分别以1.93 mm?（10a）^-1和0.11 mm?d^-1?（10a）^-1的速率显著增加, 降雪日数以2.08 d?（10a）^-1速率显著减少; 降雪量增加主要表现为各等级降雪量的增加, 降雪日数减少主要是微量和小雪日数的减少, 降雪强度增加主要为大雪和暴雪降雪强度的增加。年、 秋季和冬季降雪量占同期降水量比例平均每10年增加0.36%、 0.48%和0.45%, 春季以0.11%?（10a）^-1的速率减少。中雪、 大雪和暴雪对降雪贡献率均呈增加趋势, 小雪降雪量和微量降雪日数贡献率减少; 1987年降雪量和降雪日数突变后, 微量降雪日数和暴雪日数、 小雪降雪量贡献率改变显著。就区域平均而言, 2001 - 2017年的降雪量较1961 - 1980年增加了27.8%, 降雪日数减少了22.4%。     

刘家峡水库西南部水域表层沉积物重金属污染评价

为了研究刘家峡水库西南部水域表层沉积物中重金属的污染状况,对采集的55个表层沉积物样品中的6种重金属元素Cr、Cd、Ni、Cu、Zn和Pb的含量进行测试,其平均含量分别为77.03μg/g、0.16μg/g、33.53μg/g、32.09μg/g、291.77μg/g、22.44μg/g。在研究表层沉积物重金属含量空间分布的基础上,运用单因子污染指数法、内梅罗综合污染指数法、地累积指数法、潜在生态风险指数法,综合判断水库的受污染程度并对其潜在生态风险进行评估。6种元素的地累积指数排序依次为：Zn > Cu > Cd > Ni > Pb > Cr;潜在生态风险系数排序依次为：Cd > Cu > Pb > Zn > Ni > Cr;各区域重金属污染程度或潜在生态风险水平依次为黄河主河道 > 大夏河河口 > 黄河横剖面。综合4种方法的评价结果,认为对刘家峡水库西南部表层沉积物重金属污染及潜在生态风险评价贡献率较高的重金属污染因子是Zn、Cu和Cd;综合相关性分析与主成分分析,认为研究区沉积物重金属污染主要来源于两个方面：（1） Zn、Cu主要来源于生活污染或工业污染;（2） Cd主要来源于工农业活动产生的污染。     

A framework for the seismic assessment of existing masonry buildings accounting for different sources of uncertainty

The current formulation of Eurocode 8 Part 3 and the Italian building code for the seismic assessment of existing buildings accounts for epistemic (knowledge‐based) uncertainties by means of the identification of knowledge levels with associated values of the so‐called confidence factors, applied only as a reduction of material strengths. This formulation does not always produce consistent results and it does not explicitly account for other sources of uncertainty. The paper proposes a probabilistic methodology for the quantification of appropriately defined factors, allowing consideration of the different sources of uncertainty involved in the seismic assessment of masonry buildings by means of nonlinear static analyses. This simple approach, also including an alternative formulation of the confidence factors related with material properties, allows to obtain results which are consistent with the acquired level of knowledge and correctly account for the different sources of uncertainty without requiring to carry out any stochastic nonlinear analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Natural background levels and threshold values for groundwater in fluvial Pleistocene and Tertiary marine aquifers in Flanders,Belgium

Aquifers from the same typology can have strongly different groundwater chemistry. Deducing the groundwater quality of less well-characterized aquifers from well-documented aquifers belonging to the same typology should be done with great reserve, and can only be considered as a preliminary approach. In the EU’s 6th FP BRIDGE project “Background cRiteria for the IDentification of Groundwater thrEsholds”, a methodology for the derivation of threshold values (TV) for groundwater bodies is proposed. This methodology is tested on four aquifers in Flanders of the sand and gravel typology. The methodology works well for all but the Ledo-Paniselian aquifer, where the subdivision into a fresh and saline part is disproved, as a gradual natural transition from fresh to saline conditions in the aquifer is observed. The 90 percentile is proposed as natural background level (NBL) for the unconfined Pleistocene deposits, ascribing the outliers to possible influence of pollution. For the Tertiary aquifers, high values for different parameters have a natural origin and the 97.7 percentile is preferred as NBL. The methodology leads to high TVs for parameters presenting low NBL, when compared to the standard used as a reference. This would allow for substantial anthropogenic inputs of these parameters.     

上海短历时强降水的雷达和闪电活动特征

用雷达反射率及其导出产品(分层垂直液态水含量(VIL)、分层平均反射率等)与闪电和大气温度层结资料,通过对降水系统时间演变、反射率垂直结构和闪电活动的分析,将上海2010年6—11月的短时强降水(1 h雨量≥20 mm)分为层状暖云型、对流暖云主导型和对流冷云主导型。(1) 与雨强密切相关的关键因子是:低层(0 ℃层以下、高度在0～1 km、0～2 km、0～3 km和0～4 km)的VIL、低层(高度在1～2 km、2～3 km和3～4 km)的平均反射率和整层最大反射率;(2) 不同类型强降水中,高层(高度在0 ℃、-10 ℃和-20 ℃层以上)的VIL、整层VIL、高层(高度在5～6 km、6～7 km和7～8 km)的平均反射率、总地闪和负地闪频次这5个因子对雨强的作用各有不同;(3) 对应不同降水类型的平均反射率垂直廓线具有不同的垂直结构和发展演变特征;(4) 在三类强降水中,对流冷云主导型的雨强与总地闪和正地闪的相关性最好。      

民采空区危险性两级模糊综合评判——以招远市北截村为例

在充分搜集资料的基础上,对招远市北截村民采空区进行实地勘查,从地质条件、灾害发育程度及采空区特征3个影响因素入手,选取了9个评判因子进行两级模糊综合评判,采取最大隶属度原则确定采空区危险性等级,并进行了评估分区。评判结果能较准确地反应实际情况,为该区地质灾害防治工作及开发建设规划提供了依据。     

洞庭湖区与城陵矶水位关联性的临界特征分析

采用典型测站观测资料与水力学原理相结合,分析不同情况下城陵矶水位与洞庭湖区水位关联性强弱转化的机理和临界条件以及三峡水库对其影响等问题。理论解析表明,固定流量下,湖区水位与城陵矶水位相关关系应为单调指数函数,受到区间距离、湖槽形态等多因素影响,据此提出和率定了各湖区水位的经验计算模式。利用经验计算模式对实测数据进行延展,构建了各种可能出现的湖区来流和干流水位组合下的湖区水位特征曲线族,发现湖区水位与城陵矶水位之间的关联强度存在无影响区、影响区和决定区等状态区间,通过对临界条件的定义和计算,实现了各状态区间的定量划分,并提出了各状态区间内洞庭湖区水位的估算方法。通过对三峡水库蓄水后湖床冲淤和水文条件变化的影响分析,论证了以上方法和认识在水库蓄水后的适用性。     

不同经济水平牧户草场植被特征比较

以内蒙古荒漠草原家庭牧场为研究尺度,比较分析了不同经济水平牧户草场的植物群落特征,结果表明:主要植物种群的高度、盖度、密度、地上生物量、重要值及群落多样性指数均呈现出不同程度的趋同性.从社会学角度分析表明,牧区牧户的经济收入与饲养牲畜头数呈高度正相关.不同经济水平牧户草畜平衡的调整和适应能力不同,低经济水平牧户一般牲畜头数少,草场相对可使用面积大,经营意识薄弱,草场经常被有意或无意占用;中等经济水平牧户扩大饲养规模的愿望最为强烈,并积极通过围封、租借草场等方式来保护自家草场和扩大牲畜数量;高经济水平牧户则普遍采取常年租借草场、走场、购买饲草料等措施,减缓对自己草场放牧压力,同时保持畜饲养规模的维持和扩大.牧户存在调整适应行为,并会基于自己的“草畜平衡标准”,根据经济条件、草场面积、牲畜数量和对草场状况、放牧超载及效益的认知,适时通过草场流转和输入外部资源等方式,转移放牧压力,致使不同牧户草场生态状况趋于一致.     

Residual vorticity induced by the action of tidal currents in combination with bottom topography in the Southern Bight of the North Sea

Abstract

Results are presented of calculations on the generation of residual vorticity by tidal currents over the bottom topography of the Southern Bight of the North Sea. A typical order of magnitude is 10^?6 to 10^?7 s ^?1. This is compared with current measurements on calm days, when similar magnitudes are found. At windspeeds less than about 5 m/s tidal generation of residual vorticity is important; at higher windspeeds wind effects begin to dominate. Our results are relevant in understanding the spatial variability of residual currents, because a non-zero vorticity implies the existence of horizontal gradients in the residual current field.     

Monitoring wetland ditch water levels in the North Kent Marshes,UK, using Landsat TM imagery and ground-based measurements

Abstract

An understanding of hydrology is a prerequisite for ensuring the successful management, conservation and restoration of wetland environments. Frequently, however, little is known about historical hydrological conditions, such as water levels, within wetlands. Moreover, many channel and ditch systems in wetlands are not routinely monitored, except perhaps for research purposes. A methodology is presented herein which makes use of satellite imagery to indirectly provide remotely sensed observations of water levels within channels and ditches. Using multi-temporal Landsat Thematic Mapper (TM) imagery and simultaneous ground-based measurements of water levels, statistical relationships are established between satellite-derived effective wet ditch widths and measured water levels in the drainage system of the Elmley Marshes, southeast England. These relationships can be used subsequently to estimate historical ditch water levels and to monitor contemporary ditch water levels in the wetland. The study shows that satellite imagery has much to offer in monitoring changes in the hydrological regime of wetlands and in providing complimentary approaches to field monitoring.