1980-2016年黄河中游河龙区间植被动态及其对径流的影晌

黄河中游河龙区间是我国退耕还林／还草工程（Grain for Green Project,GGP）实施的重点区和典型区．定量评估该流域植被动态及其对径流的影响,对流域水资源可持续利用以及GGP工程的生态水文效应评价具有重要意义。该研究基于遥感、GIS技术、数理统计和布迪克弹性系数法,利用7期植被类型数据,定量评估了37年来河龙区间植被覆盖的时空变化格局及其对径流变化的影响。 结果表明：（1)植被变化并未显著地改变河龙区间各植被类型的时空分布格局;（2)GGP的实施改变了各植被类型的平衡状态和转化速度; (3）植被变化是GGP实施后10年 (2000一2010年）径流下降的主要驱动因素,但随后降水的持续增加,使得植被的“减水效应”趋于缓和。     

1956-2016年黄河流域河川径流演变规律

黄河流域水资源短缺问题突出,深入分析河川径流的演变规律对于流域水资源管理具有重要的指导意义。基于黄河干流上、中、下游不同位置的代表性水文站实测径流,利用Mann-Kendall非参数趋势检验方法分析了1956-2016年期间黄河流域年、月径流的历史演变规律。结果表明:1956-2016年,除源头区年径流变化不显著以外,黄河流域径流呈现出显著的下降趋势,达到了1%的显著性水平。从上游到下游,河川径流下降幅度越来越大,趋势越来越显著。1980-2000和2001-2016年的多年平均入海径流比1956-1979年分别减少了50. 07%和59. 67%。径流演变呈现出3阶段特征,20世纪50、60年代属于丰水期;随后在70至90年代径流持续下降;在2000年以后径流有所回升。除源头区以外,黄河流域的月径流总体呈现减少趋势;上游和中游地区的月径流占年径流的比例枯增丰减;下游地区月径流占年径流的比例在冬季、夏季增大,春季、秋季减小。     

基于人工神经网络的日径流预测

给出了用人工神经网络(ANN)对 三峡宜昌站的日径流预测模型建模的过程，对ANN输入变量的选择和个数的确定以及隐藏层 、输出层单元数的确定等关键技术问题进行了探讨。所建立的基于ANN的预测模型可以进行 提前7 d的日径流预测，预测结果令人满意。     

水资源承载力理论基础探析:定义内涵与科学问题

水资源承载力是评判水资源与经济社会及生态环境之间是否协同发展的一项综合指标,研究水资源承载力对实现人水和谐具有重要的意义。在综述水资源承载力研究进展基础上,以现阶段人类活动对水资源要素利用和水资源系统扰动的主要方式为出发点,从水量、水质、水域空间和水流状态4个维度赋予了水资源承载力新的内涵,并基于新内涵构建了水资源承载力评价指标体系。认为在水量上应以保障生态用水为前提,确定地表水可利用量和地下水可开采量阈值;在水质上应满足水功能区划水质目标及生物多样性的需求,确定保障鱼类等正常生长的浓度阈值;在水域空间上应统筹考虑防洪、生态、景观等需求,确定不同降水条件下的适宜水域面积阈值;在水流状态上应侧重水系连通对水生态的影响,确定不同水系连通指标的阈值。最后,指出水资源承载力"量-质-域-流"四维演变机制、"水资源-经济社会-生态环境"系统的承载弹性阈值、经济社会发展与生态环境保护之间的"平衡点"以及水资源承载力调控机制是水资源承载力研究的四大关键科学问题。     

Reconstruction of a long streamflow record using tree rings in the upper Kurshab River (Pamir-Alai Mountains) and its application to water resources management

A 294-year streamflow record of the upper Kurshab River was inferred from tree-ring width chronology of Turkestan juniper from the Pamir-Alai Mountains of Kyrgyzstan. The reconstructed streamflow variations were consistent with other hydrometeorological reconstructions of northern Pakistan and western Tien Shan on a decadal timescale, which demonstrate both increased and decreased streamflow intervals and trends. The new reconstruction and other hydrometeorological series successfully captured the recent wetting trend of Central Asia. Wavelet analysis indicates that decadal and interannual cycles exist in the reconstructed streamflow, which may be linked to solar activity and the North Atlantic Oscillation.     

Hydrogeochemistry,Isotopic Composition and Water Age in the Hydrologic System of a Large Catchment within a Plain Humid Environment (Argentine Pampas): Quequén Grande River,Argentina

The Quequén Grande River (QGR) is a large catchment (10 000 km²) in the Pampa Plain in Argentina. From November 2004 to April 2013, a hydrochemical and stable isotopes monitoring program was conducted, which included three sampling stations of monthly composite precipitation, weekly samples in two sites along the river and several groundwater samples. A standard data interpretation was initially performed applying standard statistics, Piper diagrams and δ¹⁸O versus δ²H diagrams. The time evolution of the values of δ¹⁸O in precipitation and streamwater were also determined. The integration of hydrogeochemistry and stable isotopes data indicates the existence of three main components of streamflow: (i) baseflow characterized by electrical conductivity (EC) from 1200 to 1800 µs/cm and an isotope composition quite constant around δ¹⁸O ?5.3‰ and δ²H ?33.8‰. Water age for groundwater contribution is typically around 30 to 40 years using chlorofluorocarbons; (ii) direct runoff composed of channel interception and overland flow, which is of low EC in the order of 50 to 100 µs/cm, and a highly variable isotopic composition; and (iii) translatory flow (pre‐event water that is stored within the subsoil) with an intermediate EC and isotopic composition close to that of the weighted average composition of precipitation. The hydrochemical and stable isotopic data allow the differentiation between baseflow and direct runoff. In addition to this, chlorofluorocarbon dating is a useful tool in assessing the dominance of baseflow in a stream. The data lead to a conceptual model in which an intermediate flow system, with mean residence time (MRT) of around 35 years, discharges into the drainage network. A regional flow system (MRT > 50 years) discharges to the ocean. It is concluded that in this large plain catchment streamflow separation, only two components can be applied in: (i) short storm precipitation events having a high sampling frequency and (ii) during long dry periods when pre‐event soil water is not released. Copyright © 2016 John Wiley & Sons, Ltd.     

Hydrologic impacts of small‐scale instream diversions for frost and heat protection in the California wine country

Though many river studies have documented the impacts of large water projects on stream hydrology, few have described the effects of dispersed, small‐scale water projects on streamflow or aquatic ecosystems. We used streamflow and air temperature data collected in the northern California wine country to characterize the influence of small instream diversions on streamflow. On cold spring mornings when air temperatures approached 0°C, flow in streams draining catchments with upstream vineyards receded abruptly, by as much as 95% over hours, corresponding to times when water is used to protect grape buds from freezing; flow rose to near previous levels following periods of water need. Streams with no upstream vineyards showed no such changes in flow. Flow was also depressed in reaches below vineyards on hot summer days, when grape growers commonly use water for heat protection. Our results demonstrate that the changes in flow caused by dispersed small instream diversions may be brief in duration, requiring continuous short‐interval monitoring to adequately describe how such diversions affect the flow regime. Depending on the timing and abundance of such diversions in a drainage network, the changes in streamflow they cause may be an important limiting factor to valued biotic resources throughout the region. Copyright © 2008 John Wiley & Sons, Ltd.     

COMPARISON OF INTERANNUAL VARIABILITY MODES AND TRENDS OF SEASONAL PRECIPITATION AND STREAMFLOW IN SOUTHERN QUEBEC (CANADA)

The interactions between precipitation, streamflow and groundwater are very complex. In cold temperate regions characterized by harsh winters, winter streamflow is mainly derived from aquifers that are recharged in the spring, during snowmelt, and in the fall, when evapotranspiration is subdued. Despite this complexity, the modes and trends in the interannual variability of spring (April, May, June and July) streamflow and fall (August, September, October and November) precipitation and streamflow were compared to the modes and trends in the interannual variability of winter (December, January, February and March) streamflow in southern Quebec from 1950 to 2000. Results indicate that the variability modes are identical for all four of these hydro‐climatic variables: two modes (south‐east and east modes) on the south shore of the St. Lawrence River on either side of the 47°N and a single mode (south‐west mode) on the north shore. As for the trend, a significant increase in winter streamflow was observed on the north shore. This increase is comparable to that observed in spring streamflow, which suggests that winter streamflow on the north shore is mainly derived from groundwater recharge during the spring. Moreover, both spring and winter streamflows are positively correlated to the North Atlantic Oscillation climate index. On the south shore, south of the 47°N, a significant decrease was observed in the trend of the interannual variability of winter streamflow, this in spite of a significant increase in fall precipitation and streamflow. An increase in evaporation (decreased infiltration) due to a shift from forest cover to agricultural land cover in this region could account for this. However, fall precipitation and streamflow and winter streamflow are significantly correlated to the Atlantic Multidecadal Oscillation winter index. This correlation is negative with the first two variables but positive with the third. This study suggests that, in southern Quebec, the interannual variability of winter streamflow is mainly affected by spring recharge in non‐agricultural catchments (east and south‐west modes) and by farming in agricultural catchments (south‐east mode). Copyright © 2011 John Wiley & Sons, Ltd.     

Temporal Variability and Potential Predictability of the Streamflow Regimes in the North‐Eastern Iberian Peninsula

This paper investigates the temporal variability and potential predictability of streamflow regimes in the north‐eastern Spain for the 1970–2010 period. Two different regimes are found, those characterized for having peak flows in the winter and those where this maximum appears in the spring. The main characteristic time scales of streamflows in each area are studied by singular spectral analysis (SSA). While winter streamflow regime only shows interannual variability (quasi‐oscillatory modes around 5.5 and 2.3 years), spring streamflow (2.6 and 6.6 years) also presents a decadal variability component. Based on this result, a modelling process is conducted using autoregressive moving average (ARMA) models, for interannual variability modelling, and stable teleconnections between global oceanic sea surface temperature (SST) anomalies and river flow, for decadal variability modelling. Finally, a one‐step‐ahead prediction experiment is computed to obtain forecasted streamflows. The results for winter streamflow regime modelling show a phase concordance between the raw and the forecasted streamflow time series of around 70% and a correlation around 0.7, for the validation period (2001–2010). For spring streamflow, additionally to the ARMA modelling for the interannual component, a model based on the SST has been established that involves some oceanic regions from previous seasons located, fundamentally, not only in the North Atlantic but also in the Indian Ocean. The combined model (SST + ARMA) significantly improves the prediction based on the ARMA model alone, showing a phase concordance and a correlation around 90% and 0.7 respectively. This modelling scheme provides predictability skills of the rivers from the Inland Catalan Basins at different time scales, representing an added value for water planning. Copyright © 2014 John Wiley & Sons, Ltd.     

Automated streamflow measurements in high-elevation Alpine catchments

Salt dilution is a well-established streamflow measurement method in creeks, which works particularly well downstream of turbulent flow sections as the mixing of the salt tracer is enhanced. Usually, salt dilution measurements are performed manually, which considerably limits the observations of rare peak flow events. These events are particularly important for constructing robust rating curves and avoiding large uncertainties in the extrapolation of streamflow values. An additional challenge is the variability of the river cross section, especially after larger discharge events, leading to nonstationary rating curves. Therefore, discharge measurements well distributed over time are needed to construct a reliable streamflow–water level relationship and to detect changes caused by erosion and deposition processes. To overcome these two issues, we used an automated streamflow measuring systems at three different sites with contrasting hydrological and hydraulic characteristics in the Alps. This system allowed us to measure discharge at nearly maximum flow of the observation period (2020–2021) at all three sites and to detect abrupt changes in the rating curve by performing event-based salt injections. The uncertainty in the measurements was quantified, and the streamflow was compared with official gauging stations in the same catchment. Based on a very large dataset of almost 300 measurements, we were able to evaluate the reliability of the system and identify the primary sources of uncertainty in the experimental setup. One key aspect was the site selection for the downstream electrical conductivity sensors, as measurement location strongly controls the signal-to-noise ratio in the recorded breakthrough curves.