北京市河流信息识别与提取

针对传统的河流信息识别和提取方法不适用于平原地区城市这一情况,该文基于北京市河流的自然和人文特征,提取城市水系网络,划分流域边界,并对河流的特征信息进行提取;从城市河流的特征识别、信息提取、空间插值等几个方面进行了总结和归纳,并从实际应用的角度进行了案例分析。研究的思路和方法可以为其他城市的相关工作提供参考。     

Comparison of basin morphometry derived from topographic maps,ASTER and SRTM DEMs: an example from Kerala,India

The drainage network of a sixth-order tropical river basin, viz. Ithikkara river basin, was extracted from different sources such as Survey of India topographic maps (1: 50,000; TOPO) and digital elevation data of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) (30 m) and Shuttle Radar Topography Mapping Mission (SRTM) (90 m). Basin morphometric attributes were estimated to evaluate the accuracy of the digital elevation model (DEM)-derived drainage networks for hydrologic applications as well as terrain characterization. The stream networks derived from ASTER and SRTM DEMs show significant agreement (with slight overestimation of lower order streams) with that of TOPO. The study suggests that SRTM (despite the coarser spatial resolution) provides better results, in drainage delineation and basin morphometry, compared to ASTER. Further, the variability of basin morphometry among the data sources might be attributed to spatial variation of elevation, raster grid size and vertical accuracy of the DEMs as well as incapability of the surface hydrologic analysis functions in the GIS platform.     

基于RS和GIS的秦岭金钱河流域露天采掘场监测研究

流域是人类活动对生态环境影响的重要监测项目。应用RS与GIS技术,对陕西省内秦岭金钱河流域露天采掘场进行动态监测,得到2007、2009和2011年3期露天采掘场开发现状数据,在此基础上,对比分析近五年来露天采掘场的变化情况,统计出露天采掘场逐年的数量和面积变化。结果表明,近五年来该流域区露天采掘场数量和面积都在逐年增加,但2009~2011年与2007~2009年相比增幅减小,说明金钱河流域露天采掘场开发活动得到了整治,生态环境质量逐渐改善。     

Spatiotemporal patterns of tropical deforestation and forest degradation in response to the operation of the Tucuruí hydroelectric dam in the Amazon basin

The planned construction of hundreds of hydroelectric dams in the Amazon basin has the potential to provide invaluable ‘clean’ energy resources for aiding in securing future regional energy needs and continued economic growth. These mega-structures, however, directly and indirectly interfere with natural ecosystem dynamics, and can cause noticeable tree loss. To improve our understanding of how hydroelectric dams affect the surrounding spatiotemporal patterns of forest disturbances, this case study integrated remote sensing spectral mixture analysis, GIS proximity analysis and statistical hypothesis testing to extract and evaluate spatially-explicit patterns of deforestation (clearing of entire forest patch) and forest degradation (reduced tree density) in the 80,000 km² neighborhoods of the Brazil's Tucuruí Dam, the first large-scale hydroelectric project in the Amazon region, over a period of 25 years from 1988 to 2013. Results show that the average rates of deforestation were consistent during the first three time periods 1988–1995 (620 km² per year), 1995–2001 (591 km² per year), and 2001–2008 (660 km² per year). However, such rate dramatically fell to half of historical levels after 2008, possibly reflecting the 2008 global economic crisis and enforcement of the Brazilian Law of Environmental Crimes. The rate of forest degradation was relatively stable from 1988 to 2013 and, on average, was 17.8% of the rate of deforestation. Deforestation and forest degradation were found to follow similar spatial patterns across the dam neighborhoods, upstream reaches or downstream reaches at the distances of 5 km–80 km, suggesting that small and large-scale forest disturbances may have been influencing each other in the vicinity of the dam. We further found that the neighborhoods of the Tucuruí Dam and the upstream region experienced similar degrees of canopy loss. Such loss was mainly attributed to the fast expansion of the Tucuruí town, and the intensive logging activities alongside major roads in the upstream reservoir region. In contrast, a significantly lower level of forest disturbance was discovered in the downstream region.     

陕北奥陶纪盐盆马五6时期东、西部盐坳沉积环境对比研究

陕北奥陶纪盐盆位于鄂尔多斯盆地伊陕斜坡东部。研究表明:马五6亚期,盐盆存在"两坳一隆"的构造格局,即东、西部盐坳和中部隆起,东、西部盐坳在钾矿化情况、溴氯系数反映的水体咸化趋势方面初步显示了陕北盐盆东、西部沉积环境的差异。本文通过东、西部盐坳典型钻井马五6层位沉积学分析,揭示了马五6时期东、西部盐坳在水体深度变化、浓缩趋势、含钾量、淡化层段厚度、陆源物质输入方面均存在差异。其中,西部盐坳受海水影响大,水体变浅且持续淡化,泥质分布反映陆源物质贡献少,对钾盐的沉积与保存均十分不利。而东部盐坳受海水影响小,与西部盐坳水体联通性差,在马五6时期环境更为封闭,具体表现为淡化夹层分布数量少、厚度薄的特征;水体持续变深并浓缩咸化;泥质夹层较多,反映了相较于西部,陆源物质对其影响更大,上述特点为钾盐沉积提供了有利的地球化学条件及可容空间。东、西部盐坳沉积环境对比表明东部盐坳对成钾更为有利。     

Interplay between an axial channel belt,slope gullies and overbank deposition in the Puchkirchen Formation in the Molasse Basin,Austria

Deep‐water sediments in the Molasse Basin, Austria, were deposited in a narrow foreland basin dominated by a large channel belt located between the steep Alpine fold and thrust belt to the south and the gentler northern slope off the Bohemian Massif. Several gas fields occur outside the channel belt, along the outer bend of a large meander. Accumulation of these overbank sediments reflects a complicated interplay between slope accommodation and debris‐flow and turbidity‐flow interaction within the channel. The tectonically oversteepened northern slope of the basin (ca 2 to 3°) developed a regionally important erosional surface, the Northern Slope Unconformity, which can be traced seismically for >100 km in an east–west direction and >20 km from the channel to the north. The slope preserves numerous gullies sourced from the north that eroded into the channel belt. These gullies were ca 20 km long, <1 km wide and ca 200 m deep. As the channel aggraded, largely inactive and empty gullies served as entry points into the overbank area for turbidity currents within the axial channel. Subsequently, debris‐flow mounds, 7 km wide and >15 km long, plugged and forced the main channel to step abruptly ca 7 km to the south. This resulted in development of an abrupt turn in the channel pathway that propagated to the east and probably played a role in forming a sinuous channel later. As debris‐flow topography was healed, flows spread out onto narrow area between the main channel and northern slope forming a broad fine‐grained apron that serves as the main gas reservoir in this area. This model of the overbank splay formation and the resulting stratigraphic architecture within the confined basin could be applied in modern and ancient systems or for subsurface hydrocarbon reservoirs where three‐dimensional seismic‐reflection data is limited. This study elucidates the geomorphology of the oversteepened slope of the under‐riding plate and its effects on the sedimentation.     

川北早寒武世碳酸盐岩台缘斜坡沉积特征及变形构造形成机制探讨

基于对川北米仓山西部旺苍县鼓城乡唐家河下寒武统仙女洞组露头剖面的观察与镜下分析发现,仙女洞组下段由生物碎屑泥晶灰岩(L)、粉砂质泥岩(M)、似瘤状砾屑灰岩(L')、角砾灰岩(R)、藻凝块灰岩(A)和含生屑钙质砂岩(S)组合而成,其以角砾灰岩、似瘤状砾屑灰岩和藻凝块灰岩为特征,且发育异地岩块和滑塌变形构造。进一步分析认为:L-M岩石组合为正常的斜坡环境低能沉积;L'-R岩石组合中的角砾灰岩为上斜坡生物灰泥丘崩坍滑动至下部而形成的,似瘤状砾屑灰岩可能是由于L-M岩石组合快速沉积导致沉积物失稳滑动变形、上斜坡生物灰泥丘崩落角砾致使的差异压实和滑动、以及后期物质成分差异引起的压溶作用等共同作用的结果,从而使灰质层发生破碎并被泥质包围形成断续的砾屑状,甚至轻微的位移,进而形成条带特征不明显的杂乱变形构造;微生物岩(Mb)组合为上斜坡的灰泥丘沉积;S-M岩石组合为斜坡上部的浊流沉积。根据上述分析结果建立米仓山西部仙女洞组碳酸盐岩台缘斜坡沉积模式,表明仙女洞组沉积早期米仓山西部存在台缘斜坡相沉积。     

Resonance of baroclinic waves in the tropical oceans: The Indian Ocean and the far western Pacific

The Indian Ocean has a particularity, its width is close to half the wavelength of a Rossby wave of biannual frequency, this coincidence having been capitalized on by several authors to give the observations a physical basis. The purpose of this article is to show that this is not the case since the resonance of tropical baroclinic waves occurs in all three oceans. This is because the westward-propagating Rossby wave is retroflexed at the western boundary to form off-equatorial Rossby waves dragged by countercurrents before receding and turning back as a Kelvin wave. Thus a quasi-stationary baroclinic wave is formed, whose mean period is tuned to the forcing period. Two independent basin modes resonantly forced are highlighted – 1) a nearly symmetric zonal 1/2-yr period Quasi-Stationary Wave (QSW) that is resonantly forced by the biannual monsoon. It is formed from first baroclinic mode equatorial-trapped Rossby and Kelvin waves and off-equatorial Rossby waves at the western antinode. This QSW controls the Equatorial Counter Current at the node. The Indian Ocean Dipole (IOD) results from a subharmonic mode locking resulting from the coupling of this QSW and the 2nd, 3rd and 4th baroclinic modes - 2) a 1-yr period QSW formed from an off-equatorial baroclinic Rossby wave, which is induced from the southernmost current of the Indonesian Throughflow through the Timor passage, propagating in the southern and northern hemispheres: the drivers are south-easterlies in the southern hemisphere and monsoon wind in the northern hemisphere.     

局地蒸发和外部水汽输送对松花江流域夏季降水的贡献

本文基于Brubaker二元模型,采用JRA-55再分析资料定量研究了局地蒸发和外部水汽输送对松花江流域夏季气候态降水及其年际变率的相对贡献,并探讨了相应的物理机制。气候平均而言,外部水汽输送是松花江流域初夏（5～6月）和盛夏（7～8月）降水的最主要水汽源。受西风带影响,初夏自西边界进入松花江流域的水汽贡献占主导,外部水汽输送对当地降水的贡献为78.9%,源自蒸发的水汽贡献为21.1%。较之初夏,由于盛夏来自南边界的水汽输送加倍,外部水汽输送贡献增加,外部水汽输送和蒸发对降水贡献分别为86%和14%。JRA-55再分析资料可以合理再现观测降水演变,1961～2016年JRA-55再分析资料降水与观测在初夏与盛夏的相关系数分别可以达到0.73和0.83。研究发现,初夏,由于西南季风异常导致的南边界进入的水汽输送异常是松花江流域降水年际变率的主要原因,自西边界、北边界进入的水汽输送与降水呈现显著负相关,初夏局地蒸发的贡献不显著,该水汽输送异常对应的环流型易发生在El Ni?o衰减年初夏。盛夏来自南边界的水汽输送起主导作用,局地蒸发贡献与降水变化显著负相关,海温强迫作用对该环流异常的强迫并不显著,中高纬度大气内部变率影响占主导。由于盛夏降水与地表温度在盛夏期间显著负相关,盛夏时期降水偏少时,温度偏高,蒸发偏强,进而蒸发水汽对降水贡献增加。     

1979—2016年四川盆地低涡的气候特征分析

利用6 h一次、水平分辨率为0.25°×0.25°的ERA-Interim再分析资料,对1979—2016年生成于四川盆地的西南涡的发生和发展进行统计分析。结果表明：四川盆地低涡集中生成于盆地内;在6月生成最多,7月发展最强;按移动情况不同可将其分为5类：东移型、东北移型、东南移型、西移型和少动型;东移型、东南移型、少动型低涡生成个数的峰值在6月,东北移型和西移型低涡生成个数的峰值在7月。夏季5类长生命史四川盆地低涡的结构和降水合成场表明：从发展强度看,东北移型最强,少动型最弱。从成熟期垂直结构看,除西移型外,低涡均随高度向西北或向西倾斜,在对流层低层为冷性结构,中层为暖性结构;东移型、东北移型、西移型低涡的正涡度区在垂直方向伸展更高;除东南移型、西移型低涡的强上升区与其中心重合外,其余类型位于其中心东侧。从降水特征看,除西移型外,其余类型低涡的降水中心均位于其移动路径东侧或东北侧,其中东北移型低涡成熟期6 h累计降水量最大。四川盆地低涡的强上升区、相对湿度大值区、位于对流层低层和中层的辐合辐散中心与降水所在位置有很好的对应关系,各物理量场相互作用共同促进低涡发展。