沙坡头地区气候变化特征及其功能谱分析

论文探讨了沙坡头地区气候要素的年际、年内变化特征,并采用功能谱分析方法,定量分析了气温、降水的周期性变化规律,得出气温年际变化具有８．４ａ、３．５ａ和２．８ａ的周期规律;降水年际变化具有８．４ａ、５￣６ａ、３．５ａ和３ａ的周期性规律。采用交叉功能谱分析方法研究了气温与降水协同变化机制、周期性及其对人工植被的影响,得出降水和气温组合因子具有１０．５ａ、８．４ａ、３．５￣３．８ａ的波动周期。为气候资源     

太湖流域全新世气候-海面短期振荡事件及其对新石器文化的影响

太湖流域埋藏古树、泥炭、贝壳堤和新石器文化遗址,＾１４Ｃ年代频率变化揭示了全新世气候－海面波动与文明兴衰的时间耦合关系。本区降水量的明显增加始于８ｋａＢ．Ｐ．、７．５￣４ｋａＢ．Ｐ．总的看为高海面和新石器文化发展时期,但其间有相对的海面波动,即：７￣６．５ｋａＢ．Ｐ．为高海面期、６．３￣５．６ｋａＢ．Ｐ．为低海面期、４．５￣４ｋａＢ．Ｐ．为低海面期、３．８￣３．５ｋａＢ．Ｐ．为高海面期。从文化断层     

黄土地区气候演变的有机地球化学标志

对渭南阳敦黄土剖面Ｓｏ￣Ｌ２层段作了总有机碳（ＴＯＣ）和Ｒｏｃｋ－Ｅｖａｌ热解烃分析，建立了ＴＯＣ气候变化曲线及其变化周期，与其它气候指标进行了对比，揭示了黄土剖面中与气候变化有关的两种烃类，推导并验证了古湿度公式，计算了各层段的湿度分布及其演变趋势。     

石笋有机碳作为气候指标的初步研究

利用总碳分析仪对云南寻甸仙人洞1号石笋(编号XR1)有机碳含量进行分析,初步建立了总碳分析仪分析石笋有机碳的方法,并利用寻甸仙人洞XR1有机碳分析结果重建了寻甸地区全新世中期有机碳气候变化模式,其与XR1石笋的氧同位素气候变化模式结果一致.通过石笋有机碳含量与石笋氧碳同位素和石笋沉积速率的对比,发现石笋有机碳含量与石笋...     

东南沿海地区旱涝气候准周期振荡特征及其变化趋势

本文提出干旱指数与洪涝指数二分序列，讨论了东南沿海地区１４７０￣１９９３年时间序列上旱，涝气候准周期振荡特征。结果表明，旱的周期振动与涝的周期振动存在着差异，在不同的时间尺度上都有所反映，作周期分析时有必要分别寻求旱与涝各自的周期振动分量，结果表明，太阳活动１１年周期，２２年磁周期和日月地相对运动１９年周期，都与该区旱涝长期变化存在着较强的统计对应关系，并且太阳活动强弱世纪周期对其长期变化也有一定     

长江源区地表水资源对气候变化的响应及趋势预测

利用1961-2011 年长江源区流域水文、气象观测数据和国家气候中心2009 年11 月发布的中国地区气候变化预估数据集(2.0 版本), 通过分析长江源区流量的演变规律和揭示气候归因, 预测了未来流量可能的演变趋势。研究表明:近51 年来长江源区地表水资源总体呈增加趋势, 特别是2004 年后增加趋势显著, 并具有9a、22a 的准周期;青藏高原加热场增强, 高原季风进入强盛期, 流域降水量显著增加, 加之气候变化导致冰川融水增多, 是引起长江源区地表水资源增加的主要气候归因;根据全球气候模式预测, 在SRESA1B气候变化情景下, 未来20年长江源区地表水资源仍有可能以增加为主。     

太湖流域公元960年以来的气候干湿变化研究

利用史料和文献建立了太湖流域公元960-1992年的逐年干湿等级序列，对此序列进行了周期分析和突变分析。分析表明，本区近千年来的历史干湿气候变化是一种复合振动，其主周期是准100年，另外还有多个周期，这些周期与天体活动密切相关。统计还发现1247-1263年附近由干变湿和1618-1635年附近由湿变干的两次非局地性气候突变事件。其中，14、15世纪是太湖流域近千年来最湿润的时期，它可能是东亚地区大范围气候变湿波动的体现。     

基于EEMD的明代北京地区干旱灾害特征分析

集合经验模态分解（EEMD）是一种适用于非线性、非平稳序列的信号分析方法,将EEMD应用于气候要素时间序列,可提取真实可靠的气候变化信号。根据北京地区历史时期干旱灾害资料,采用EEMD分解方法对明代（1368—1644年）北京地区干旱灾害等级序列进行多时间尺度的分析,获得简洁且平稳性较好的固有模态函数分量,并与所统计的明代北京地区干旱灾害频次多项式拟合曲线进行对比。结果表明：将EEMD应用于干旱灾害等级序列,可以提取干旱灾害中各个尺度的变化,对明代北京地区干旱灾害进行多尺度分析。明代北京地区干旱灾害存在着2.8年、6.3年的年际周期,11.5年、26.6年、53.6年的年代际周期和118.7年、299.5年的世纪周期。北京地区干旱灾害在明代整个时间跨度上呈现着先增加后微减的变化趋势,总体而言明代中期以后旱灾明显增多。     

末次冰期盛期中国热带的变迁

参照约６０个实例,探讨末次冰期盛期中国热带位置的纬度地带性和经度地带性变迁。当时,热带中部、热带北部、亚热带南部３个地带的北界分别南移５个、２个、６个纬距。经度地带性差异可分为５个区。其年均温下降幅度,台湾岛最大（５￣９℃）,两广及海南岛其次（３￣４℃）,闽南粤东较小（２￣３℃）,滇南最小（１￣２℃）。南海冬季水温降幅较大（２．４￣５．７℃）。除闽南、粤东、南海趋于冷干外,大部分地区环境趋于冷湿。     

祁连山东段北麓近10ka来的气候变化初步研究

磁化率、碳酸钙含量和有机碳含量可用作良好的气候指标,主要是反映了降水量的变化。祁连山东段北麓哈溪剖面研究表明,９５６０ａＢ．Ｐ．时本区已进入全新世。大暖期是对温度而言,与气候适宜期是不同的概念,二者在时间上也不一定是同时的。本区的气候适宜期为６．８～３．６ｋａＢ．Ｐ．,气候最宜期为５．０～３．６ｋａＢ．Ｐ．,与其它记录有不同之处。在７．８～７．２ｋａＢ．Ｐ．和１．５～０．８ｋａＢ．Ｐ．间出现了“冷湿”的气候组合,这与传统的气候组合不同,但后一阶段的“冷湿”是有大量证据的。９．０～８．７ｋａＢ．Ｐ．间是全新世最干旱的时段,堆积了砂黄土。     

The characteristics of turbulence in a shear zone downstream of a channel constriction in a coarse-grained forced pool

A field-based project was initiated to characterize the influence of varying discharge and bed topography along a pool exit-slope on the strength of turbulence generated by vortex shedding. Velocities were measured with an ADV downstream of a boulder constriction within a shear zone of a large pool. Measurements were repeated for four flows that varied from 20% to 50% of bankfull discharge. An additional longitudinal profile was conducted along the pool thalweg. Plots of velocity demonstrate high near-bed velocities and turbulence levels in the pools. Turbulence levels were highest closer to the constriction in the shear zone. Turbulent kinetic energy decayed in the downstream direction in response to the bed topography and at lower discharges. Instantaneous velocities are large enough to temporarily lift pebbles at this depth. It appears that instantaneous forces created by vortex shedding may play an important role in scouring pools downstream of constrictions. The turbulence may also respond to changes in bed topography in a manner that encourages feedbacks among bed topography, characteristics of turbulence, and sediment transport.     

2008年6月广西锋前暖区暴雨过程分析

利用常规观测资料、卫星TBB和NCEP再分析资料,对2008年6月8-13日持续性暖区暴雨的环流特征、影响系统及物理量变化进行了诊断分析,结果表明:本次暴雨过程是在高层200hPa出现环流型调整、500hPa贝加尔湖至新疆地区为弱阻高形势和地面锋面低槽的环境下产生的,主要影响系统有低层切变线和低涡;低空急流迅速建立、北抬,使低层风速辐合加强是产生锋前暖区暴雨的有利因素;广西的中尺度环境存在南北明显差异,可能是形成双雨带的主要原因;在切变线和低涡切变锋区上垂直运动结构有明显差异,低涡切变上低层辐合高层强辐散,上升运动更强烈;暴雨前相对湿度明显增大,湿层深厚,中高层相对湿度在降水减弱时率先出现下降趋势;水汽通量中心的出现与暴雨发生时段和暴雨落区较为对应;夏季风向北推进,华南地区发生经向风扰动,出现了季风涌,使南海的水汽和能量源源不断地传送到华南地区,为这次持续性暴雨提供有利条件。     

Medium-term evolution of a gully developed in a loess-derived soil

Field surveys in the Belgian loess belt revealed the presence in many forested areas of large, permanent gully systems, most of which are currently inactive. In cultivated areas, such gullies can only be observed in cross-sectional soil profiles through hollows, as virtually all such large gullies are currently infilled with colluvium. Little is known about the spatial distribution, initiation and temporal evolution of these large, permanent gully systems on loess-derived soils. Therefore, the medium-term evolution of a gully initiated in a cultivated area on loess-derived soils southwest of Leuven (Belgium) in May–June 1986, was studied over 13 years. Two intense rainfall events created this (ephemeral) gully, which was not erased by subsequent tillage. Between June 1986 and the December 1999, eight field surveys were conducted to measure gully dimensions. During two surveys, topographic indices (e.g., slope and drainage area) were also measured. Daily rainfall for the measuring period were obtained from a rainfall station located some 10 km southwest of the gully. Analysis of rainfall data showed that no extreme rainfall event was required to initiate such large (permanent) gullies, as observed in forested areas and through cross-sectional profiles in cultivated fields in the Belgian loess belt. Return periods of the event that caused the gully varied between <1 year and 25 years, depending on the assumptions used for defining event rain intensity. Once established, length, surface area and volume of the studied gully evolved with time, cumulative rainfall or cumulative runoff, following a negative exponential relation. This accords with observations reported for gullies in Australia and the USA. This study shows that a degressive increase of gully extension, can be largely explained by the evolution of a “slope–drainage area” factor (S×A, which is proportional to stream power) with time. While gully length and gully surface area asymptotically evolve towards a final value, gully volume decreased at a given point in time. From this, it is inferred that sediment deposition will potentially infill the gully to such an extent that the farmer can drive across it. From this moment on, the combined effect of water and tillage erosion in the gully drainage area, will lead towards rapid infilling. This expected evolution of a gully in cultivated fields accords with observations of large infilled gully systems in cultivated areas in eastern Belgium. The permanent gullies observed under forest are attributed to the fact that after severe gully erosion, this area was reforested or abandoned. Therefore, the sediment source was cut off and the gully was not filled in by sediment deposition.     

Creating and coupling a high-resolution DTM with a 1-D hydraulic model in a GIS for scenario-based assessment of avulsion hazard in a gravel-bed river

In this paper we explore the development and assimilation of a high resolution topographic surface with a one-dimensional hydraulic model for investigation of avulsion hazard potential on a gravel-bed river. A detailed channel and floodplain digital terrain model (DTM) is created to define the geometry parameter required by the 1D hydraulic model HEC-RAS. The ability to extract dense and optimally located cross-sections is presented as a means to optimize HEC-RAS performance. A number of flood scenarios are then run in HEC-RAS to determine the inundation potential of modeled events, the post-processed output of which facilitates calculation of spatially explicit shear stress (τ) and level of geomorphic work (specific stream power per unit bed area, ω) for each of these. Further enhancing this scenario-based approach, the DTM is modified to simulate a large woody debris (LWD) jam and active-channel sediment aggradation to assess impact on innundation, τ, and ω, under previously modeled flow conditions. The high resolution DTM facilitates overlay and evaluation of modeled scenario results in a spatially explicit context containing considerable detail of hydrogeomorphic and other features influencing hydraulics (bars, secondary and scour channels, levees). This offers advantages for: (i) assessing the avulsion hazard potential and spatial distribution of other hydrologic and fluvial geomorphic processes; and (ii) exploration of the potential impacts of specific management strategies on the channel, including river restoration activities.     

Sustainability in a materials world

Many adverse impacts on the environment can be directly related to the materials dispersed to the environment during processing or use, or after use as refuse and waste. Some materials, such as toxic wastes, are a major concern because they create immediate problems with longerterm effects. Gases released by major manufacturing industries can contribute to long-term regional and global problems such as acid rain or increased carbon dioxide in the atmosphere. The use of other materials, however, appears to be more benign or strictly localized in their impacts. If the current per capita level of material consumption in the United States was achieved worldwide, it would create major stresses on both resource adequacy and the environment. In fact, stresses have been created and will continue from this consumption style (developed countries) even if others don't achieve them.Correspondence should be directed to Earle B. Amey, U.S. Geological Survey, National Center 983, Reston, Virginia 20192.     

黄土丘陵沟壑区典型小流域土地持续利用案例研究

本文选择我国水土流失最为严重的黄土丘陵沟壑区作为研究地区,通过野外调查、土地利用填图,结合区域国民经济发展规划提出了4种基本土地利用规划方案附加2种保护性耕作措施;开展了生态适宜性、经济可行性和社会可接受性评价。提出:在得到大量外部经济支持的前提下,应积极实行15°以上的坡耕地全部退耕还林还草的方案,其中在中等坡度的地区(15°-25°)应发展果园和经济林;若缺少外部强有力的经济支持,该区土地利用调整应逐步开展,短期内(约0-5年),建议坡度大于25°的坡耕地逐步退耕还林还草,其中,坡度大于25°,地形条件较好的地区应种植果园和经济林;中期(约5-10年),坡度大于20°的黄土地区应逐步退耕还林还草,其中坡度介于20°-25°之间的地区应转变为果园和经济林;10年之后,建议大于15°的坡耕地全部转变为其他用途,其中坡度介于15°-25°的黄土地区应转变为果园和经济林,坡度大于25°的地区转变为林地/灌丛和草地