Geomorphic process from topographic form: automating the interpretation of repeat survey data in river valleys

The ability to quantify the processes driving geomorphic change in river valley margins is vital to geomorphologists seeking to understand the relative role of transport mechanisms (e.g. fluvial, aeolian, and hillslope processes) in landscape dynamics. High‐resolution, repeat topographic data are becoming readily available to geomorphologists. By contrasting digital elevation models derived from repeat surveys, the transport processes driving topographic changes can be inferred, a method termed ‘mechanistic segregation.’ Unfortunately, mechanistic segregation largely relies on subjective and time consuming manual classification, which has implications both for its reproducibility and the practical scale of its application. Here we present a novel computational workflow for the mechanistic segregation of geomorphic transport processes in geospatial datasets. We apply the workflow to seven sites along the Colorado River in the Grand Canyon, where geomorphic transport is driven by a diverse suite of mechanisms. The workflow performs well when compared to field observations, with an overall predictive accuracy of 84% across 113 validation points. The approach most accurately predicts changes due to fluvial processes (100% accuracy) and aeolian processes (96%), with reduced accuracy in predictions of alluvial and colluvial processes (64% and 73%, respectively). Our workflow is designed to be applicable to a diversity of river systems and will likely provide a rapid and objective understanding of the processes driving geomorphic change at the reach and network scales. We anticipate that such an understanding will allow insight into the response of geomorphic transport processes to external forcings, such as shifts in climate, land use, or river regulation, with implications for process‐based river management and restoration. Copyright © 2017 John Wiley & Sons, Ltd.     

Watershed structural influences on the distributions of stream network water and solute travel times under baseflow conditions

Watershed structure influences the timing, magnitude, and spatial location of water and solute entry to stream networks. In turn, stream reach transport velocities and stream network geometry (travel distances) further influence the timing of export from watersheds. Here, we examine how watershed and stream network organization can affect travel times of water from delivery to the stream network to arrival at the watershed outlet. We analysed watershed structure and network geometry and quantified the relationship between stream discharge and solute velocity across six study watersheds (11.4 to 62.8 km²) located in the Sawtooth Mountains of central Idaho, USA. Based on these analyses, we developed stream network travel time functions for each watershed. We found that watershed structure, stream network geometry, and the variable magnitude of inputs across the network can have a pronounced affect on water travel distances and velocities within a stream network. Accordingly, a sample taken at the watershed outlet is composed of water and solutes sourced from across the watershed that experienced a range of travel times in the stream network. We suggest that understanding and quantifying stream network travel time distributions are valuable for deconvolving signals observed at watershed outlets into their spatial and temporal sources, and separating terrestrial and in‐channel hydrological, biogeochemical, and ecological influences on in‐stream observations. Copyright © 2016 John Wiley & Sons, Ltd.     

山东荣成湾月湖口门落潮干道的推移质输运

改进了Gao等 ( 1 994)方法 ,并用以计算潮汐汊道口门落潮干道的垂线平均流速。利用月湖潮汐汊道系统冬、夏季各一个月的潮位资料 ,计算落潮干道的潮流流速和推移质输运率。结果表明 ,流速的计算值和实测值呈良好的相关性 ,落潮干道内落潮流的输沙能力高于涨潮流输沙能力     

Stream nitrate uptake and transient storage over a gradient of geomorphic complexity,north‐central Colorado,USA

The understanding of nutrient uptake in streams is impeded by a limited understanding of how geomorphic setting and flow regime interact with biogeochemical processing. This study investigated these interactions as they relate to transient storage and nitrate uptake in small agricultural and urban streams. Sites were selected across a gradient of channel conditions and management modifications and included three 180‐m long geomorphically distinct reaches on each of two streams in north‐central Colorado. The agricultural stream has been subject to historically variable cattle‐grazing practices, and the urban stream exhibits various levels of stabilisation and planform alteration. Reach‐scale geomorphic complexity was characterised using highly detailed surveys of channel morphology, substrate, hydraulics and habitat units. Breakthrough‐curve modelling of conservative bromide (Br^?) and nonconservative nitrate (NO₃^?) tracer injections characterised transient storage and nitrate uptake along each reach. Longitudinal roughness and flow depth were positively associated with transient storage, which was related to nitrate uptake, thus underscoring the importance of geomorphic influences on stream biogeochemical processes. In addition, changes in geomorphic characteristics due to temporal discharge variation led to complex responses in nitrate uptake. Copyright © 2011 John Wiley & Sons, Ltd.     

南亚高压次季节尺度东西振荡对我国长江流域降水及水汽输送的影响

使用常规资料及HYSPLIT(Hybrid Single Particle Lagrangian Integrated Trajectory Model)模式,分析了早夏和晚夏期间南亚高压次季节尺度异常偏东事件和异常偏西事件发生时,我国长江流域降水及水汽输送异常特征。结果表明:早夏期间当南亚高压异常东伸时,西太平洋副热带高压可西伸至我国东南沿岸,此时,降水正异常场主要位于我国东部地区,表现为江淮区域降水异常偏多;而晚夏期间当南亚高压异常东伸时,西太平洋副热带高压的西脊点更偏东,降水正异常区位置比早夏偏西,表现为四川盆地的降水异常偏多。早夏期间,与南亚高压异常偏西事件相比,南亚高压异常偏东事件有利于更多的水汽从南方的水汽源地输送到我国江淮区域,加上此时江淮流域存在异常上升运动,动力和水汽条件共同使得江淮流域降水偏多。晚夏四川盆地地区有类似的结论。     

基于区域航空运输可达性的机场空间布局

构建表现机场腹地与其航空运输网络间相互关系的结构方程模型,明确“二三产业总产值/总人口数/社会消费品零售总额”与“通航机场数/航班密度/通航里程”2个变量组之间的数量关系。基于腹地陆路交通网络和机场航空运输网络,列出机场陆域可达性和航线可达性的数学表达式,并基于乘客的主观感受组合2类可达性指标得到区域航空运输可达性指标,将该指标作为比选机场空间布局方案的标准。以烟台/威海地区为例对不同机场布局方案的场景进行分析,结果表明：在目前的需求形态下烟台/威海地区应设置1个机场,以使旅客享有较好的航空运输服务,使整个区域的航空运输可达性最优。     

Discharge and suspended sediment flux estimated along the mainstream of the Amazon and the Madeira Rivers (from in situ and MODIS Satellite Data)

Water and suspended sediment fluxes are considered during the period 2000–2008 in a region including the full Amazon River from the confluence of the Negro River to Santarém, the end part of the Solimões River, and the lower part of the Madeira River. Three types of data are used: water discharge estimated from field measurements, and suspended sediment obtained from field measurements and derived from MODIS satellite data. A generalized least square method including a propagating term is developed in order to propagate the signal upward and downward the river. The approach is introduced and tested. Several experiments are considered in order, first, to estimate the ability to propagate the signal from stations located before the confluences of Negro and Madeira Rivers to stations located on the Amazon River; second to investigate the possibility to propagate the signal along the Amazon River which dynamics is coupled with floodplains dynamics; and third to produce optimal solutions of water and sediment fluxes. For each experiment, the influence of field and satellite data is compared. The approach is efficient in the upper part of the region of study where the Solimões, the Negro and the Madeira Rivers meet and fails in the lower part of the region where interactions between Amazon River and floodplains play an important role on the fluxes’ dynamics. The optimal experiment includes in situ and satellite data from all the stations available and is used to analyse the recent evolution of suspended sediment flux along the Amazon River and its interaction with the large coupled floodplains. A high accumulation rate is observed during the 2000–2002 period, followed by decreasing rates until 2005 and by increasing values in 2006 and 2007. Our results suggest that floodplains extending along a river reach of 390 km-long between Itacoatiara and Óbidos trap about 15% of the suspended sediment flux passing at Óbidos. The simulated deposition rate is of about 0.3 Mt km⁻¹ yr⁻¹ corresponding to an accretion rate of about 27 mm yr⁻¹.     

利用被动示踪物模拟对黑潮入侵南海的数值研究

由于缺少观测数据和对黑潮水准确定义,很难识别出从太平洋入侵到南海的黑潮水团。本文基于一个经过观测验证的三维模式MITgcm,利用被动示踪物标记黑潮水,研究了入侵南海的黑潮水的时空变化。研究表明,在冬季,黑潮水入侵的范围最广,几乎占据了18°N-23°N和114°E-121°E的区域;并有一个分支进入台湾海峡;黑潮入侵的范围随深度增加逐渐减小。在夏季,黑潮水被限制在118°E以东,且没有分支进入台湾海峡;入侵的范围从海面到约205米是增大的,之后随深度增加逐渐减小。通过分析从2003年到2012年黑潮入侵的年际变化,与厄尔尼诺年和正常年相比,冬季黑潮入侵后向台湾海峡的分支在拉尼娜年是最弱的,这可能与中国大陆东南方向的风应力旋度有关。通过吕宋海峡的黑潮入侵通量（KIT）是西向的,其年平均值约为-3.86×10⁶ m³/s,大于吕宋海峡通量（LST,约-3.15×10⁶ m³/s）。250米以上的KIT约占了全深度通量的60-80%。此外,从2003年到2012年KIT与Niño 3.4指数的相关系数到达0.41,小于LST与Niño 3.4指数的相关系数0.78。     

论气候变暖背景下干旱和干旱灾害风险特征与管理策略简

The drought is a most severe natural disaster worldwide, which leads to great risk in human being. The drought disaster and risk have more prominent because of obvious climatic warming in the last hundred years. At present, the understanding of the internal laws of the occurrence of drought and drought risk is not comprehensive, and the recognition of the characteristics of the drought and drought risk under climatic warming is obscure. In this paper, we summarized systematically the domestic and overseas research progress of the drought and drought disaster risk, introduced the principle of the drought disaster transfer process and the essential features of drought disaster, analyzed synthetically the main characteristics and interactions among the key factors of the drought disaster risk, discussed the effect of climatic warming on drought and drought disaster risk, and probed into the basic requirement of drought disaster risk management. Above all, we provide the main protective measurements of the drought disaster and the main strategy of drought disaster risk management.