Search

The use of electrical resistivity tomography (ERT; non-intrusive geophysical technique) was assessed to identify the hydrogeological conditions at a surface water/groundwater test site in the southern Black Forest, Germany. A total of 111 ERT transects were measured, which adopted electrode spacings from 0·5 to 5 m as well as using either Wenner or dipole-dipole electrode arrays. The resulting two-dimensional (2D) electrical resistivity distributions are related to the structure and water content of the subsurface. The images were interpreted with respect to previous classical hillslope hydrological investigations within the same research basin using both tracer methods and groundwater level observations. A raster-grid survey provided a quasi 3D resistivity pattern of the floodplain. Strong structural heterogeneity of the subsurface could be demonstrated, and (non)connectivities between surface and subsurface bodies were mapped. Through the spatial identification of likely flow pathways and source areas of runoff, the deep groundwater within the steeper valley slope seems to be much more connected to runoff generation processes within the valley floodplain than commonly credited in such environmental circumstances. Further, there appears to be no direct link between subsurface water-bodies adjacent to the stream channel. Deep groundwater sources are also able to contribute towards streamflow from exfiltration at the edge of the floodplain as well as through the saturated areas overlying the floodplain itself. Such exfiltrated water then moves towards the stream as channelized surface flow. These findings support previous tracer investigations which showed that groundwater largely dominates the storm hydrograph of the stream, but the source areas of this component were unclear without geophysical measurements. The work highlighted the importance of using information from previous, complementary hydrochemical and hydrometric research campaigns to better interpret the ERT measurements. On the other hand, the ERT can provide a better spatial understanding of existing hydrochemical and hydrometric data. Copyright © 2009 John Wiley & Sons, Ltd.

We want to develop a dialogue between geophysicists and hydrologists interested in synergistically advancing process based watershed research. We identify recent advances in geophysical instrumentation, and provide a vision for the use of electrical and magnetic geophysical instrumentation in watershed scale hydrology. The focus of the paper is to identify instrumentation that could significantly advance this vision for geophysics and hydrology during the next 3–5 years. We acknowledge that this is one of a number of possible ways forward and seek only to offer a relatively narrow and achievable vision. The vision focuses on the measurement of geological structure and identification of flow paths using electrical and magnetic methods. The paper identifies instruments, provides examples of their use, and describes how synergy between measurement and modelling could be achieved. Of specific interest are the airborne systems that can cover large areas and are appropriate for watershed studies. Although airborne geophysics has been around for some time, only in the last few years have systems designed exclusively for hydrological applications begun to emerge. These systems, such as airborne electromagnetic (EM) and transient electromagnetic (TEM), could revolutionize hydrogeological interpretations. Our vision centers on developing nested and cross scale electrical and magnetic measurements that can be used to construct a three-dimensional (3D) electrical or magnetic model of the subsurface in watersheds. The methodological framework assumes a ‘top down’ approach using airborne methods to identify the large scale, dominant architecture of the subsurface. We recognize that the integration of geophysical measurement methods, and data, into watershed process characterization and modelling can only be achieved through dialogue. Especially, through the development of partnerships between geophysicists and hydrologists, partnerships that explore how the application of geophysics can answer critical hydrological science questions, and conversely provide an understanding of the limitations of geophysical measurements and interpretation. Copyright © 2008 John Wiley & Sons, Ltd.

is the combined outcome of both the 2001 EGS ses-sion on the ‘Water balance of mountain basins’ in Nice and the 2002 Annual Meeting of the Ger-man Hydrological Working Group in Berlin. A variety of hydrological and meteorological research top-ics presented at these meetings focused on water resources, modelling, parameterization, remote sens-ing, snow and ice melt, evaporation and transpiration. Case studies concentrated especially on moun-tain areas, which ranged in altitude from 1500 to 6000 m, and on a variety of regions, such asthe Himalayas, Karakorum, Hindukush, Yemen Mountain Massif, Norwegian Scandes and Alps. Theanalysis of water balance components was conducted at many different temporal and spatial scales,ranging from annual and seasonal to daily and hourly, and from entire basins to single lysimetricanalyses.The current discussion about climatic–hydrologic change and bio-adaptability reflects the necessityfor more comprehensive and more detailed knowledge about water balance in mountain basins. Sincemountain watersheds are source areas for large rivers, an understanding of the water balance is invalu-able. This should include a variety of components, such as water input, water storage, water loss, andwater transfer potentials on steep, heterogeneous surfaces. Many of the associated processes are insuf-ficiently investigated, although they are of major significance for both hydrologists and water resourcemanagers.AIMIt is the aim of this special issue to present a diverse range of topics and research areas in order to revealthe wide spectrum of research topics and methods on water balance studies in mountain basins. These stud-ies demonstrate both the success and the emerging difficulties and shortcomings in different research fields.Examples from the developed and from the developing world not only promote comparisons, but also newideas about the availability and transferability of methods.

This paper reports some of the achievements in hydrological research associated with the Mackenzie GEWEX Study (MAGS). MAGS is a multifaceted study of the energy and water cycle in the Mackenzie River Basin, north-western Canada, and emphasizes cold-region processes and modelling. It pursues methodologies of scaling-up process studies to a large river basin that has few measurement sites. This methodology involves new developments, adapting mid-latitude algorithms to the high latitude setting and promoting the use of remote sensing tools for scaling-up. Intensive hydrological process studies have been concentrated at a number of sites. These have been chosen to represent different biophysical facets of the Mackenzie River Basin. They include northern basins in open tundra and at tree-line, a western basin representing the hilly and mountainous western side of the basin, central basin sites of wetlands, Precambrian Shield terrain and the Mackenzie Basin counterpart of the large Laurentian Great Lakes. The most southerly site represents a mixed-wood boreal forest site that is undergoing land-use change as a result of forest harvesting. Regional community model analysis indicates that processes of lee cyclogenesis result in differential input of precipitation across the basin. Significant results centre on models of snow accumulation featuring the role of blowing snow, intercepted snow and snowmelt. These models emphasize the importance of snow patchiness to speed of melt. Snowmelt infiltration into frozen soils is important in controlling runoff, and tundra microlandforms play a unique role in determining the surface runoff characteristics. On the western margins of the basin, there is a very significant difference in the hydrological behaviour of slopes of different aspects as a result of differences in permafrost and vegetation. In the central basin, a deeper understanding of components of the water budget is being gained through stable isotope analysis of wetland waters.

Copyright © 2013 John Wiley & Sons, Ltd. Introduction Tropical dry forests have lived in the shadow of their humid counterparts with respect to scientific research. Despite accounting for more than 42% of all tropical forest (Murphy and Lugo, 1995) and roughly 6% of the Earth’s land surface, less than 15% of the literature on all tropical forest research has focused on tropical dry forests with the remainder highlighting work in tropical wet forests (Sanchez-Azofeifa et al., 2005; Santos et al., 2011). Many of these tropical dry forest regions are currently water stressed, and additional pressures from population growth, land use and future climate change will have significant implications for the future functioning of their natural and socioeconomic systems. In spite of the recognized importance ofwater resources in the tropics, there have been remarkably few publications on the hydrological processes in this region as compared to the humid temperate zone (e.g. Bonell, 1993, 1998; Buttle et al., 2009;Ohte andTokuchi, 2011; Price, 2011). This is especially true for tropical dry forests, which is surprising given that surface runoff is often limited to a 3 – 5month period annually, with an intervening dry period with little to no precipitation (Ortiz-Jimenez et al., 2005; Love et al., 2010). Hence, there is a critical need to understand the hydrology of tropical dry forests, particularly in light of current land use and future climate change issues facing these regions. In this, commentary we will highlight the

Machine learning (ML) models, and Long Short-Term Memory (LSTM) networks in particular, have demonstrated remarkable performance in streamflow prediction and are increasingly being used by the hydrological research community. However, most of these applications do not include uncertainty quantification (UQ). ML models are data driven and may suffer from large extrapolation errors when applied to changing climate/environmental conditions. UQ is required to ensure model trustworthiness, improve understanding of data limits and model deficiencies, and avoid overconfident predictions in extrapolation. Here, we propose a novel UQ method, called PI3NN, to quantify prediction uncertainty of ML models and integrate the method with LSTM networks for streamflow prediction. PI3NN calculates Prediction Intervals by training 3 Neural Networks and uses root-finding methods to determine the interval precisely. Additionally, PI3NN can identify out-of-distribution (OOD) data in a nonstationary condition to avoid overconfident prediction. We apply the proposed PI3NN-LSTM method in both the snow-dominant East River Watershed in the western US and the rain-driven Walker Branch Watershed in the southeastern US. Results indicate that for the prediction data (which have similar features as the training data), PI3NN precisely quantifies the prediction uncertainty with the desired confidence level; and for the OOD data where the LSTM network fails to make accurate predictions, PI3NN produces a reasonably large uncertainty bound indicating the untrustworthy result to avoid overconfidence. PI3NN is computationally efficient, reliable in training, and generalizable to various network structures and data with no distributional assumptions. It can be broadly applied in ML-based hydrological simulations for credible prediction.

Until recently, the development of a global geography of floods was challenged by the fragmentation and heterogeneity of in situ data and the high costs of processing large amounts of remote sensing data. Such geography would facilitate the exploration of large-scale drivers of flood extent and timing including wide latitudinal, climate, and topographic effects. Here we used a monthly dataset spanning 30 years (Global Surface Water Extent) to develop a worldwide geographical characterization of slow floods (1-degree grid), weighting the relative contribution of seasonal, interannual, and long-term fluctuations on overall variability, and quantifying precipitation-flooding delays where seasonality dominated. We explored the dominance of different flooding timings across five Köppen-Geiger main climates and seven topography classes derived from modeled water table depths (i.e., hydro-topography) to contribute top-down insight about the outstanding, cross-regional flooding patterns and their likely large-scale drivers. Our results showed that, globally, the mean extent of floods averaged 0.48% of the global land area, predominantly associated with hydro-topography (>2x more extensive in flatter landscapes). Climate drove flood timings, with predictable, seasonally-dominated fluctuations in cold regions, interannual and mixed patterns in temperate climates, and more irregular (higher variability) and unpredictable (less seasonal) patterns in arid regions. Net gains of flooded area dominated temporal variability in 9% of the cells including boreal clusters likely affected by warming trends. We propose that this new geographical perspective of floods can aid different avenues of hydrological research in the upscaling and extrapolation of field studies and the parsimonious representation of floods in hydroclimatic models.

Hydrology plays a central role in applied and fundamental environmental sciences, but it is well known to suffer from an overwhelming diversity of models, particularly to simulate streamflow. We discuss here in detail how such diversity did arise based on the example of Switzerland. The case study's relevance stems from the fact that Switzerland, despite of being a small country, shows a variety of hydro-climatological regimes, of water resources management challenges, and of hydrological research institutes that led to a model diversification that stands exemplary for the diversification that arose also at larger scales. Our analysis, based on literature review, personal enquiry and an author survey, summarises the main driving forces behind model diversification. We anticipate that this review not only helps researchers from other fields but in particular also the international hydrology community to understand why we have so many different streamflow models.

Dissolved gases, including noble gases, are versatile environmental tracers. Historically, the application of dissolved (noble) gases as tracers in hydrology used to be limited because their measurement required expensive, laboratory-based instrumentation operated by highly trained personnel. Here, we highlight recent advances in mobile mass spectrometry (MS) methods for noble and other dissolved gases, which enable low cost, high-throughput, real-time measurements. We also present applications using mobile MS to quantify hydrological and biogeochemical processes in groundwater and surface waters and to assess hazards and risks to aquatic environments. Finally, we indicate potential future applications of these instruments to enhance hydrological research.

The Jalovecký Creek catchment, Slovakia (area 22.2 km², mean elevation 1500 m a.s.l.), is likely the last big valley complex in the Carpathian Mountains, in which the hydrological cycle is still governed by natural processes. Hydrological research is conducted there since the end of the 1980s. The overall mission of the research is to increase the knowledge about the hydrological cycle in the highest part of the Carpathians. The research agenda, briefly introduced in the first part of this article, is focused on water balance, snow accumulation and melt and runoff formation. Recent analysis of precipitation, discharge, snow cover and isotopic data from period 1989–2018 indicates that hydrological cycle has become more dynamic since 2014. Although several indicators suggest that it could be related to the cold part of the year, direct links with snow storage and the contribution of snowmelt water to catchment runoff were not confirmed. The second part of the article is therefore focused on an analysis of daily cycles in streamflow in March to June 1988–2018 to obtain a deeper insight into the snowmelt process. We describe characteristics of the cycles and examine their variability over the study period. The results indicate that less snow at the lowest elevations (800–1150 m a.s.l.) since 2009 could have influenced the cessation of the cycles in June since 2010. The possible role of the decreased amount of snow at the lowest elevations in changes in runoff characteristics is also suggested by an increase in time lags between maximum discharges during the events and maximum air temperatures preceding discharge maxima measured near the catchment outlet (at 750 m a.s.l.) in spring 2018 compared to springs with a similar number of streamflow cycles in the years 1988, 2000 and 2009. Wavelet analysis did not indicate changes in global power spectra in hourly discharge and air temperature data.

The Marcell Experimental Forest (MEF) in northern Minnesota, USA, with hydrological research and monitoring of peatland catchments in a low-topographic relief landscape, contrasts with the mountainous terrain that typifies most research catchments. Six research catchments were instrumented and hydrological and meteorological monitoring was initiated during 1960. Paired-catchment studies, which started during 1969, have been used to assess land management and environmental change effects on forests, water availability, and biogeochemistry. Over the decades, the research and collaborations have proliferated to include new monitoring and ecosystem experiments. We provide an overview of available datasets and access information for hydrological and meteorological data. Data on streamflow, water table elevation, precipitation, snow, ground frost, air temperature, soil moisture, upland runoff, and water chemistry are discoverable with associated metadata and are archived through several Web-based, community repositories. The research programme is ongoing and we anticipate updates on an annual or more frequent basis. Additionally, we aim to release other physical, chemical, and isotopic measurements associated with long-term catchment monitoring and studies at the MEF.

Drought has a complex climatic and spatio-temporal feature. Therefore, its accurate monitoring is a great challenge for hydrological research. Recently, the use of standardized drought indices (SDIs) for drought monitoring is common in practice. However, because of the subjective choices of probability distribution, the uncertainty related to extreme events always exists in SDIs-based drought-monitoring tools. The present research extends the generalized non-parametric framework for drought monitoring. The application of the proposed framework is based on seven meteorological stations in Pakistan. The preliminary analysis considered the standardized precipitation temperature index (SPTI) at different time scales. The significance of the proposed framework is to address extreme values with more accuracy under a non-parametric framework. It is concluded that the suitable choice of probability-plotting-position formulas allows greater accuracy when capturing the probability of extreme drought events.

Understanding cryospheric hydrology and the effects of cryospheric changes on river runoff is critical for sustainable water management especially in arid inland river basins such as those in northwest China where water resources mainly come from alpine areas. A cryospheric hydrometeorology observation system (CHOICE) has been established since 2008 in the Hulu catchment, which is a well-instrumented experimental and representative catchment in the upper reaches of the inland Hei River, Qilian Mountains, northwest China. The CHOICE includes dense meteorological measurements from 2980 to 4800 m asl (e.g. glacier, snow, and permafrost hydrology) and water and heat balance in the vertical landscape zones including alpine grassland, meadow, shrub, coniferous forest, marshy meadow, and moraine-talus zones. The comprehensive long-term observations available for the CHOICE provide the basis for model development and application in cryospheric hydrological research. We focus on cryospheric hydrometeorological process of precipitation, freeze–thaw cycle, energy balance, soil–vegetation–atmosphere transfer (SVAT), runoff, groundwater reservoir, and hydrological resiliency within vertical elevation in CHIOCE. Data from CHOICE, an open cryospheric hydrology observation and research system, is accessed through a website (/) and the WestDC database (/).

Recent growth in the capabilities of unmanned aerial vehicles and systems (UASs) as airborne platforms for collecting environmental data has been very rapid. There are now ample examples in the literature of UASs being deployed to map fine-scale vegetation, glacial, soil and atmospheric conditions. The purported advantages of UASs are their ability to collect spatial data at lower cost, lower risk, higher resolution and higher frequency than ground surveys or satellite platforms. In this specific study, whether or not obtaining high-resolution UAS imagery was advantageous for identifying an intermittent stream network was determined by comparing it with coarse-scale satellite imagery collected for the same purpose. It was also determined if the UAS imagery could be an improvement to Global Positioning System acquired ground-truth points for classifying an intermittent stream network across the same large-scale satellite image. The UAS-acquired and satellite-acquired imageries were derived from a visible spectrum camera capable of 2-cm resolution and multispectral SPOT-5 with 10-m resolution, respectively. The SPOT-5 imagery with its relatively coarse resolution could not always detect the narrow intermittent stream, which was well resolved in the UAS imagery. When a classified UAS image was applied as a training area for the SPOT-5 image, the identification of the stream network and accuracy of the satellite imagery classification did not necessarily improve. UASs have the potential to revolutionize hydrological research the same way that geographic information systems did three decades ago. A final goal of the paper is to provide insight into the advantages and disadvantages of deploying a UAS for this kind of research. © 2015 Her Majesty the Queen in Right of Canada. Hydrological Processes. © 2015 John Wiley & Sons, Ltd.

During the last decades of the 19th century, a great worry arose about forest landscape paludification in Northern Sweden. This was the original impetus for forest hydrological research in Sweden, and the Swedish Institute of Experimental Forestry established the first field research site in 1905 at Rokliden, close to Pitea in North Sweden. It comprised 8.64 ha located 2 km down a 3-km-long gently sloping (~4%), north facing Norway spruce covered till slope, interspersed with small mires. By 1931, it was concluded that paludification was not spreading across Northern Sweden at an appreciable rate. Within the Rokliden research site, 22 groundwater wells were installed and levels measured weekly until 1926. A map with 0.5 m equidistance, ten vegetation classes, and soil profiles was established. Groundwater flow velocity was estimated by tracing added sodium chloride. Hydraulic conductivity was measured on undisturbed soil cores, while mechanical and chemical analyses were carried out on other samples. Groundwater was collected and analysed for dissolved compounds including oxygen. Hydrology was found important for soil types and vegetation development. The necessary profile drainage for podzol soil development was identified as vein drainage at the bedrock surface. Modern measurements in the re-established groundwater observation network and re-analysis of old data confirmed the plausibility of these original conclusions. Partial catchment area could explain rates of both groundwater level rise and recession. Revisiting this field study reveals that many issues in contemporary hillslope hydrology were already established a century ago, even though the provenance of that knowledge is not generally recognized. Copyright © 2014 John Wiley & Sons, Ltd.

Few systematic studies of valley-scale geomorphic drivers of streamflow regimes in complex alpine headwaters have compared response between catchments. As a result, little guidance is available for regional-scale hydrological research and monitoring efforts that include assessments of ecosystem function. Physical parameters such as slope, elevation range, drainage area and bedrock geology are often used to stratify differences in streamflow response between sampling sites within an ecoregion. However, these metrics do not take into account geomorphic controls on streamflow specific to glaciated mountain headwaters. The coarse-grained nature of depositional features in alpine catchments suggests that these landforms have little water storage capacity because hillslope runoff moves rapidly just beneath the rock mantle before emerging in fluvial networks. However, recent studies show that a range of depositional features, including talus slopes, protalus ramparts and ‘rock-ice’ features may have more storage capacity than previously thought. To better evaluate potential differences in streamflow response among basins with extensive coarse depositional features and those without, we examined the relationships between streamflow discharge, stable isotopes, water temperature and the amplitude of the diurnal signal at five basin outlets. We also quantified the percentages of colluvial channel length measured along the stepped longitudinal profile. Colluvial channels, characterized by the presence of surficial, coarse-grained depositional features, presented sediment-rich, transport-limited morphologies that appeared to have a cumulative effect on the timing and volume of flow downstream. Measurements taken from colluvial channels flowing through depositional landforms showed median recession constants (Kr) of 0.9–0.95, δ 18 O values of ≥� 14.5 and summer diurnal amplitudes ≤0.8 as compared with more typical surface water recession constant values of 0.7, δ 18 O ≤ � 13.5 and diurnal amplitudes >2.0. Our results demonstrated strong associations between the percentage of colluvial channel length within a catchment and moderated streamflow regimes, water temperatures, diurnal signals and depleted δ 18 O related to groundwater influx. Copyright © 2014 John Wiley & Sons, Ltd.

Hydrological processes of lakes in the Tibetan Plateau are an important indicator of climate change. Due to the high elevation, inaccessibility and limited availability of historical observations, water budget evaluation of typical lake basins has been inadequate. In this study, stable isotopes are used to trace the multiple water sources contributing to two adjacent lakes on the north slope of the Himalayas, Gongmo-tso and Drem-tso. The two lakes have nearly the same elevation, lake area and climatic condition. However, the isotopic composition of the two lakes presents significant differences. Qualitative observations attribute the differences to hydrological discrepancies: Gongmo-tso is a through-flow lake, whereas Drem-tso is a terminal lake. Quantitative analyses, including water and isotope mass balance modelling, clarify the fluxes and isotopic compositions among the various hydrological elements. The isotopic composition of input water, calculated as the summation of rainfall and upstream runoff, is estimated using the local meteoric water line (LMWL) combined with the time series of lake water isotope values. The isotopic composition of evaporation is calculated with a linear resistance model using local meteorological data. The results show that Drem-tso is a closed lake in a hydrological steady state with relatively more enriched lake water isotope values resulting mainly from evaporation. In contrast, through-flow accounts for more than 88% of the water input into Gongmo-tso. The large amount of upstream runoff with lower isotopic composition and enrichment due to evaporation are the major contributions to the observed lake water isotope values. Isotopic modelling of the two neighbouring lakes is effective for isotopic and hydrological research in this region with limited in situ observations. Copyright © 2013 John Wiley & Sons, Ltd.

Kundzewicz, Zbigniew W., 2011. Nonstationarity in Water Resources – Central European Perspective. Journal of the American Water Resources Association (JAWRA) 47(3): 550-562. DOI: 10.1111/j.1752-1688.2011.00549.x Abstract: Nonstationarity in variables describing water quantity and water quality characteristics is reviewed, and an attempt to interpret nonstationary behavior is made with particular reference to the Central European region. Nonstationarity in water-related variables results from several nonclimatic and climatic factors. Albeit evidence of climate change in Central Europe is clear, anthropogenic nonclimatic change, such as land-use or land-cover changes, water engineering measures, and in-catchment water management play important roles. Systemic socioeconomic and political changes are the main factors responsible for the observed change in water quality in the region. The observed climate change in the Central European region has not been dramatic enough to persuade the water management community that changes of standards, criteria, and evaluation procedures should be made. Projections for the future largely differ between models and scenarios, hence information obtained from climate models is found too vague to be used. However, the water management community shows interest in climate change observations, projections, and impact assessments. Numerous hydrological research projects to tackle nonstationarity have been undertaken in the region. Also important acts of legislation, such as the European Union’s Water Framework Directive and Floods Directive can be regarded in the context of nonstationarity of water-related variables.

An essential part of hydrological research focuses on hydrological extremes, such as river peak flows and associated floods, because of their large impact on economy, environment, and human life. These extremes can be affected by potential future environmental change, including global climate change and land cover change. In this paper, the relative impact of both climate change and urban expansion on the peak flows and flood extent is investigated for a small-scale suburban catchment in Belgium. A rainfall-runoff model was coupled to a hydrodynamic model in order to simulate the present-day and future river streamflow. The coupled model was calibrated based on a series of measured water depths and, after model validation, fed with different climate change and urban expansion scenarios in order to evaluate the relative impact of both driving factors on the peak flows and flood extent. The three climate change scenarios that were used (dry, wet winter, wet summer) were based on a statistical downscaling of 58 different RCM and GCM scenario runs. The urban expansion scenarios were based on three different urban growth rates (low, medium, high urban expansion) that were set up by means of an extrapolation of the observed trend of urban expansion. The results suggest that possible future climate change is the main source of uncertainty affecting changes in peak flow and flood extent. The urban expansion scenarios show a more consistent trend. The potential damage related to a flood is, however, mainly influenced by land cover changes that occur in the floodplain. Copyright © 2011 John Wiley & Sons, Ltd.

Regional classification techniques can help in identifying spatial structure in river flow variation. As such, a framework can be provided around which to test hypotheses, making regional classification an important tool for hydrological research, particularly over large and complex geographical domains. Here, the results of a regional classification of monthly river flow for the northern North Atlantic region over the period 1968–1997 are presented. Importantly, regional classes are identified on the basis of inter-annual variation in river flow time series, rather than the more commonly used intra-annual flow regime. This is beneficial because it provides an improved basis for the investigation of regional-scale inter-annual trends in river flow: an important aim given the potential for future changes in river discharge linked to climate change and land-use change. Seven regions (four in northern Europe and three in eastern North America) are identified using hierarchical cluster analysis (Wards algorithm). Analysis of the hydrological homogeneity of the emergent river flow regions reveals them to be useful groupings to frame further analyses. Investigation of the statistical characteristics of each mean regional time series follows, including the annual flow regime, time series variability, and the presence of trends (as indicated by the Mann-Kendall test). Key findings identified by the latter analysis include an increasing trend in late winter discharge for some northern European regions for 1968–1997, but overall few statistically significant trends. Copyright © 2010 John Wiley & Sons, Ltd.

To minimize potential loss of life and property caused by rainfall during typhoon seasons, precise rainfall forecasts have been one of the key subjects in hydrological research. However, rainfall forecast is made difficult by some very complicated and unforeseen physical factors associated with rainfall. Recently, support vector regression (SVR) models and recurrent SVR (RSVR) models have been successfully employed to solve time-series problems in some fields. Nevertheless, the use of RSVR models in rainfall forecasting has not been investigated widely. This study attempts to improve the forecasting accuracy of rainfall by taking advantage of the unique strength of the SVR model, genetic algorithms, and the recurrent network architecture. The performance of genetic algorithms with different mutation rates and crossover rates in SVR parameter selection is examined. Simulation results identify the RSVR with genetic algorithms model as being an effective means of forecasting rainfall amount. Copyright © 2006 John Wiley & Sons, Ltd.

The distribution of stable water isotopes provides valuable insight into runoff generation processes in subarctic wetland regions of the Mackenzie River basin, a major freshwater contributor to the Arctic Ocean and the focus of intensive hydrological research as part of Canada's contribution to the Global Energy and Water Cycle Experiment (GEWEX). This article describes a streamfiow hydrograph separation analysis carried out over three complete annual cycles (1997-1999) for five subarctic catchments ranging in size from 202 to 2050 km 2 situated near the confluence of the Liard and Mackenzie rivers. This heterogeneous landscape, characterized by extensive wetlands (fen and bog), shallow lakes and widespread discontinuous permafrost, is representative of vast flow-contributing areas of the upper Mackenzie Valley, and is suspected to be highly sensitive to climate variability and change. We document seasonal patterns and interannual variability in the isotopic composition of local streamflow, attributable to mixing of three distinctly labelled flow sources, namely groundwater, surface water plus rain, and direct snowmelt, and apply these isotopic signals to partition sources and their temporal variability. Although groundwater input is the dominant and most persistent streamflow source in all five catchments throughout the year, direct snowmelt runoff via surface and shallow subsurface pathways (during spring freshet) and surface waters from lakes and wetlands situated in low-lying areas of the basins (during summer and fall) are also significant seasonal contributors. Catchment-specific differences are also apparent, particularly in the generation of snowmelt runoff, which is more attenuated in fen-dominated than in bog-dominated catchments. The data set additionally reveals notable interannual variability in snow isotope signatures and snow water equivalent, apparently enhanced by the 1998 El Nino event.

Increasing demand for timber products results in the expansion of commercial afforestation in South Africa. The conversion of indigenous seasonally dormant grassland to evergreen forests results in increased transpiration and ultimately a reduction in catchment runoff, creating a negative impact on the country's scarce water supplies. In order to assist managers in the decision-making processes it is important to be able to accurately assess and predict hydrological processes, and the impact that land use change will have on water resources. The Soil and Water Assessment Tool (SWAT) provides a means of performing these assessments. One of the key strengths of the SWAT model lies in its ability to model the relative impacts of changes in management practices, climate and vegetation on water quantity and quality. The aim of this study was to determine if the SWAT model could reasonably simulate hydrological processes in daily time steps from two small South African catchments. To verify the SWAT model a grassland (C VIgrass) and Pinus patula afforested catchment (C IIpine) were selected from the Cathedral Peak hydrological research station in the KwaZulu Natal Drakensberg mountains. These catchments were chosen because of the availability of detailed hydrological records and suitable land use. Observed and simulated streamflow for C VIgrass and C IIpine were compared. When model fits of observed and simulated streamflow for C VIgrass were acceptable, this parameter set was then used in the configuration of C IIpine. Results show that the model performs well for C VIgrass with reasonable agreement between modelled and observed data (R2 = 0·68). Comparisons for C IIpine show a total oversimulation of streamflow for the period 1950 to 1965, with deviations between observed and modelled data increasing from 1959 to 1965, due to the model not accounting for the increase in ET brought about by the maturing pine plantation. Copyright © 2005 John Wiley & Sons, Ltd.

Wetlands comprise 14% of the land area of Canada. They have considerable impact on water storage and runoff, water quality, atmospheric exchanges of carbon, and important elements such as nitrogen. In less remote parts of Canada, wetlands have suffered from reclamation, exploitation, contamination and degradation, which have seriously impaired their ecological function. Public recognition of their environmental significance has highlighted the need for a better understanding of the hydrological processes, to better plan and manage wetland areas, restore degraded systems, and predict responses to global change. This paper reviews current hydrological research in all types of Canadian wetlands. The scope of hydrological processes discussed herein includes runoff, surface and groundwater flows, evaporation, microclimate, water balance, geochemical and solute transport phenomenon, carbon dynamics, isotope studies, exploitation and restoration. Field, laboratory and modelling studies are included. Copyright © 2000 John Wiley & Sons, Ltd.

Topographic characteristics computed from 100- and 1000-m resolution digital elevation model (DEM) data are compared for 50 locations representing varied terrain in the conterminous USA. The topographic characteristics are three parameters used extensively in hydrological research and modelling—slope (S), specific catchment area (As) and a wetness index computed as the logarithm of the specific catchment area divided by slope [ln(As/S)]. Slope values computed from 1000-m DEMs are smaller than those computed from 100-m DEMs; specific catchment area and the wetness index are larger for the 1000-m DEMs compared with the 100-m DEMs. Most of the differences between the 100- and 1000-m resolution DEMs can be attributed to terrain-discretization effects in the computation of the topographic characteristics and are not the result of smoothing or loss of terrain detail in the coarse data. In general, the terrain-discretization effects are greatest on flat terrain with long length-scale features, and the smoothing effects are greatest on steep terrain with short length-scale features. For the most part, the differences in the average values of the topographic characteristics computed from 100- and 1000-m resolution DEMs are predictable; that is, biases in the mean values for the characteristics computed from a 1000-m DEM can be corrected with simple linear equations. Copyright © 2000 John Wiley & Sons, Ltd.

Digital elevation models (DEMs) are becoming increasingly important tools in hydrological research and in water resources management. The quality of DEMs, however, normally is reported simply as the root mean square error of elevation, a statistic that fails to capture the numerous sources of error in DEMs or to predict their effect on the result of using the DEM. This paper presents a review of other approaches to assessing DEM quality, and argues that a full assessment of DEM quality must focus on the accuracy and reliability of the final product of the DEM analysis. A number of DEMs for the Slapton Ley catchments in Devon derived from digitized contour data are compared in an initial assessment of their sustainability for use in hydrological work. Two are available for purchase from data suppliers, and five more were created using a variety of interpolation techniques in widely available geographical information system software. The different interpretation methods produce DEMs with different artefacts, although analyses of the distribution of elevation values, and visual techniques, suggested that none of these were of a particularly pronounced nature. The results of using the DEMs to derive drainage networks and catchment areas showed that at the broad scale there was a high level of agreement between the DEMs. There were, however, important differences of detail. For example, some DEMs predicted drainage lines that occasionally crossed the original contours. The results of calculating the TOPMODEL topographic index showed far more variation, because the index is calculated for each pixel in the area, rather than being an aggregate result derived from numerous pixels. The main conclusion was that care should always be taken to assess the quality of a DEM before attempting to use it, and that results should always be checked to ensure that they appear to be reasonable. Copyright © 2000 John Wiley & Sons, Ltd.

Chinese people have long recognized the importance of forests and water in environment, societal development, and civilization. The philosophical thoughts are well reflected in many ancient paintings and stories that picture the harmony of forests, water, and mountains, and in fact, well-respected Chinese rulers are known for their contributions to harnessing large rivers such as the mighty Yellow and the Yangtze Rivers in China’s 5,000 years’ history. Unfortunately, China’s natural forests and water resources have been severely damaged in the past century due to overpopulation, years of wars, mismanagement and exploitative use, and global environmental change. As a result, China has suffered chronic environmental problems at the national scale, notably soil erosion, flooding, and water pollution and shortage in its recent history. While China’s unprecedented socioeconomic growth increasingly stresses forest and water resources, it also provides opportunities to reverse earlier damage. In the past three decades, China has implemented several nationwide forest restoration and protection programs such as the ‘‘Three North Shelterbelts Project,’’ the ‘‘Natural Forest Protection Programme,’’ and the ‘‘Green for Grains Program’’ that aim at reducing soil erosion and flooding, improving water quality, and curbing further ecosystem degradation. Although a full assessment of the projects’ success is not available, it is widely believed that they have resulted in positive effects on water resources and overall ecosystem health of headwaters of major river basins. Thanks to massive forestation campaigns, China has the largest plantation forests (53 million ha, an area larger than California) in the world, and its annual growth in man-made forests accounts for over half of the global total. Last year alone, more than two billion trees were planted in China (http://english.people.com. cn/90001/90776/90882/6371092.html). Forest hydrological research to guide these large ecosystem restoration efforts is urgently needed. Assessments of the effects of forestry policy changes on water resources are well sought by the Chinese government to effectively manage both water and forest resources. Forest hydrology research in China has been limited and western literature was not readily available before the early 1980s when China began economic reform and adopted an ‘‘open-door’’ policy. Since then, large progress has been made in the understanding of forests’ role in regulating the hydrological cycle across the vast landscape of this populous nation. Focus was

Digital flow networks derived from digital elevation models (DEMs) sensitively react to errors due to measurement, data processing and data representation. Since high-resolution DEMs are increasingly used in geomorphological and hydrological research, automated and semi-automated procedures to reduce the impact of such errors on flow networks are required. One such technique is stream-carving, a hydrological conditioning technique to ensure drainage connectivity in DEMs towards the DEM edges. Here we test and modify a state-of-the-art carving algorithm for flow network derivation in a low-relief, agricultural landscape characterized by a large number of spurious, topographic depressions. Our results show that the investigated algorithm reconstructs a benchmark network insufficiently in terms of carving energy, distance and a topological network measure. The modification to the algorithm that performed best, combines the least-cost auxiliary topography (LCAT) carving with a constrained breaching algorithm that explicitly takes automatically identified channel locations into account. We applied our methods to a low relief landscape, but the results can be transferred to flow network derivation of DEMs in moderate to mountainous relief in situations where the valley bottom is broad and flat and precise derivations of the flow networks are needed. Copyright © 2013 John Wiley & Sons, Ltd.

An horizontal und vertikal entnommenen Stechzylinderproben wurden gesattigte Wasserleitfahigkeit Kf. Lagerungsdichte und Porengrosenverteilung einer unterschiedlich beweideten Salzmarsch im Deichvorland auf die isotrope Verteilung der Werte im Raum hin untersucht. Die Ergebnisse zeigen, das die gesattigte Wasserleitfahigkeit signifikant anisotrope Variation aufweist. Das Kv/Kh Verhaltnis betragt 0.38 bei Betrachtung der gesamten Profile und 0.44 fur Oberboden. Diese Anisotropie ist wesentlich auf die geogene Wechselschichtstruktur der Sedimente zuruckzufuhren und wird immer geringer mit Fortschreiten der Bodenstrukturierung durch pedologische Prozesse. Die Beweidung hat signifikante Auswirkung auf die Kf−Werte ab einer Intensitat von 1.0 SE/ha. Diese Auswirkung ist im deichnahen Bereich starker ausgepragt als im deichfernen. Die Kv- und Kh-Werte werden jedoch gleichermasen von der Beweidung beeinflust, so das die anisotrope Variation der Kf von der Beweidung unabhangig ist. Lagerungsdichte und Makroporositat (> 10 μm) der oberen Tiefen werden ebenfalls von der Beweidung signifikant beeinflust, aber nicht von der Richtung der Probenahme. Kf korreliert signifikant mit dem Anteil an > 50 μm bzw. > 10 μm Poren. Die Korrelation zwischen Kf und der gesamten Porositat ist nicht signifikant. Die Anisotropie der Kf bedeutet eine Begunstigung des lateralen Wasserflusses in der Salzmarschhydrologie und sollte daher in der Okosystemforschung und Modellierung des Wasser- und Stoffhaushaltes der Salzmarschen berucksichtigt werden. Anisotropic variation of saturated hydraulic conductivity of a variously grazed salt marsh soil Undisturbed core samples were taken in horizontal and vertical direction from a variously grazed salt marsh soil for investigation of the anisotropic variation of saturated hydraulic conductity Ksat, bulk density, and pore size distribution. The results show that saturated hydraulic conductivity varies significantly anisotropically. The average Kv/Kh ratio is 0.38 for the soil profile and 0.44 for the surface soil. This anisotropy of Ksat is mainly attributed to the stratified structure of soil due to the sedimentation conditions in the salt marsh environment and decreases if soil structure development through pedological processes progresses. Furthermore. Ksat decreases significantly if the stocking rate of grazing is larger than 1.0 sheep unit/ha and the effect is more pronounced near the dike. However, both the Kv and Kh are affected by grazing in the same manner, so that the anisotropy of Ksat is independent from grazing. Bulk densitiy and macroporosity are affected by grazing but not by the direction of sampling. There are significant correlations between Ksat and > 50 μm as well as > 10 μm pore volume. The correlation between Ksat and total porosity is however not significant. The anisotropy of Ksat implicates the favouring of the lateral water flux and in the hydrological research and modelling of the salt marsh ecosystem the anisotropy of Ksat should be taken into account.

A hierarchical sampling programme (including continuous monitoring, twice-daily sampling and sampling at hourly intervals over selected 24 hour periods) was devised to support hydrochemical and hydrological research programmes on an alpine proglacial stream. The rationale for the research and for the sampling programme are explained and the hydrochemical time series generated over an ablation season are analysed to assess the degree to which they support the study aims. It appears that there is no satisfactory substitute for the chemical analysis of at least two water samples taken at approximately maximum and minimum discharge every day, if seasonal variations in meltwater chemistry are to be effectively characterized. Such time series data can be used to estimate Box-Jenkins transfer function-noise models between particular solutes (SO2−4, Ca2+, Mg2+, Na+ and possibly K+) and either discharge or electrical conductivity, which can then be used to fill any short gaps in the data. This approach is not satisfactory even for filling short gaps in the twice-daily determinations of pH, HCO−3 and NO−3. At the diurnal time-scale (based on hourly determinations over 24 hour periods) electrical conductivity seems to provide a good surrogate for most of the solutes studied. HCO−3, SO2−4, Ca2+ and Mg2+ were found to be particularly strongly related to electrical conductivity and there was little if any significant serial autocorrelation in the residuals from all of the simple linear regression relationships that were estimated between individual species and conductivity. It is concluded that the hierarchical sampling design was suitable for the purposes of the study, and that the continuous monitoring of electrical conductivity provides excellent supporting information to the chemical analysis of water samples if it is used carefully as a means of short term calibration and interpolation of the solute record.