bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaporation of Intercepted Rainfall
Authors: David Jorge Soares , Valente Fernanda , Gash John HC 
Published: April 2006

AbstractWhen rain falls on to a vegetated surface (gross rainfall), a part is intercepted by the canopy and evaporated directly back into the atmosphere (interception loss). The remainder of the rainfall reaches the ground (net rainfall) either through gaps and by dripping from the canopy (throughfall), or by running down the main stem (stemflow). The canopy storage capacity is the minimum amount of water necessary to completely saturate the canopy surface. Interception loss is conventionally measured as the difference between the incident gross rainfall, and the sum of throughfall and stemflow. It is usually a significant component of the overall evaporation and may play an important role in watershed water balance. The total amount of interception loss depends on the rate of evaporation from the wet canopy, the canopy storage capacity, and the distribution and intensity of rainfall. Interception loss is particularly high in forests due to their high aerodynamic roughnesses. Available models range from empirical relationships to physically based conceptual models. Within the latter, the Rutter‐type models are those that have been taken up as the more generally applicable technique. Most of the models rely on the use of the Penman–Monteith equation to estimate the evaporation rate. Current research is largely directed at modeling in horizontally heterogeneous vegetation, where the Penman–Monteith equation may not be valid.
Characterizing Forest Canopy Structure and Ground Topography Using Lidar
Authors: Dubayah Ralph , Peterson Birgit , Rhoads Joshua , Dietrich William E 
Published: April 2006

AbstractRemote sensing observations increasingly are used to obtain the detailed information needed about land surface state required for hydrological analyses. However, many of the surface state parameters required for such analyses are related to the vertical structures of surface vegetation and topography, that are often difficult to measure using passive optical and radar remote sensing technologies. A new technology, lidar (light detection and ranging) remote sensing, has proven highly effective for characterizing land surface structure in great detail, including subcanopy topography, canopy height, foliar profile and biomass, among others. In this article, we review the theory and application of lidar remote sensing for characterizing land surface states for hydrological analysis. First we present a brief overview of lidar, and discuss similarities and distinctions between the small‐footprint systems commonly used in commercial applications and large‐footprint approaches used in research and space‐based systems. We next describe common land surface variables that are often used in hydrological analysis and how these are related to vertical structures observable from lidar. Lastly, we present how lidar may be used to recover or parameterize these surface variables; in particular we focus on the observation of forest and topographic structures.
Estimation of Snow Extent and Snow Properties
Authors: Hall Dorothy K , Kelly Richard EJ , Foster James L , Chang Alfred TC 
Published: April 2006

AbstractImportant advances have been made in the measurement of seasonal snow cover since the advent of satellite remote sensing in the mid 1960s. Data from the visible, near‐infrared, infrared, and microwave portions of the electromagnetic spectrum have proven useful for measuring different properties of snow. In terms of snow mapping, sensors employing visible and near‐infrared wavelengths are now capable of accurately and reliably measuring snow‐cover extent with a spatial resolution of up to 250 m on a daily basis, and even higher resolution for less‐frequent coverage. Passive‐microwave data, available since the 1970s, have been utilized for measuring snow extent, depth and snow‐water equivalent (SWE), though at a coarse spatial resolution compared to visible data, while active‐microwave sensors such as scatterometers, provide valuable information on snowpack ripening. Capabilities of synthetic‐aperture radar (SAR) data for snow‐cover studies are still being explored, however, bands on current satellite SAR sensors are not ideal for measuring snow cover. Remote sensing data of snow cover are now well suited for use in hydrologic and general‐circulation models. Inclusion of remotely‐sensed data significantly enhances our understanding of the Earth's weather and climate, and decadal‐scale climate change. Future improvements include refinement of snow‐cover extent measurements, minimizing SWE errors, and improving our ability to ingest remote sensing data of snow into models.
Soil Hydraulic Properties
Authors: Durner Wolfgang , Flühler Hannes 
Published: April 2006

AbstractThe accurate knowledge of hydraulic properties for unsaturated soils is critical in addressing problems in a variety of disciplines such as hydrology, ecology, environmental sciences, soil science, and agriculture. The purpose of this paper is to review the characterization of unsaturated soil hydraulic properties for their applicability in models simulating unsaturated water transport. In a theoretical section, we present the fundamentals for the definitions of the hydraulic properties in the framework of the continuum theory as well as provide the common parameterizations of the hydraulic functions. The characterization and parameterization of hysteresis and the phenomenon of dynamic effects in hydraulic properties are addressed in subsequent sections. Finally we discuss issues related to the handling of spatial and temporal variability, including geostatistical characterization, upscaling, and scale dependency of effective properties. The review closes with a summary on limits and opportunities for modeling water transport with Richards' equation.
Models of Water Flow and Solute Transport in the Unsaturated Zone
Authors: Šimůnek Jirka 
Published: April 2006

AbstractA large number of models for simulating water flow and solute transport in the unsaturated zone are now increasingly being used for a wide range of applications in both research and management. Modeling approaches range from relatively simple analytical and semianalytical solutions, to complex numerical codes. While analytical and semianalytical solutions are still popular for some applications, the ever‐increasing power of personal computers and the development of more accurate and numerically stable solution techniques have motivated much wider use of numerical codes in recent decades. The wide use of numerical models is also significantly enhanced by their availability in both the public and commercial domains, and by the development of sophisticated graphics‐based interfaces that can tremendously simplify their use.In this paper I focus mainly on numerical models, give a brief history of their development, and discuss some of the more often used numerical techniques including relatively efficient matrix solvers that now are available for multidimensional models. Names and web addresses of some of the more popularly used numerical codes simulating vadose zone processes are also provided. Finally, some typical problems in which the numerical codes have been applied are identified.
Sediment Yield Prediction and Modeling
Authors: White Sue 
Published: April 2006

Abstract
The estimation of sediment yield – the amount of sediment reaching or passing a point of interest in a given period of time – is an inherently complex and uncertain science as it is the integrated outcome of erosion, sediment transport, and deposition processes through an often complex landscape. Thus, sediment yield can vary greatly from year to year with variation in climate, land use, and land management. A range of estimation techniques have been developed ranging from simple empirical relationships between sediment yield and river flow or basin characteristics, through methods to scale soil erosion estimates or measurements using delivery ratios, to physically based distributed models. Descriptions of the various approaches, together with advantages and shortcomings of these methods, are given. For prediction of future sediment yields, the uncertainties are even greater as climate and land‐use pressures are not easily defined for hypothetical situations. Here, recommendations are made to incorporate uncertainty into the prediction and decision‐making process.
Suspended Sediment Transport – Flocculation and Particle Characteristics
Authors: Droppo Ian G 
Published: April 2006

Abstract
In the history of sediment transport research within hydrological sciences, there has possibly been no greater paradigm shift than that which has been provided by the identification of flocculation as a dominant mechanism operating within, and mediating, cohesive suspended sediment transport. Flocculation (the process of aggregating smaller particles together to form larger particles) significantly modifies the hydrodynamic properties of the sediment by altering their effective size, shape, density, porosity, and composition. Such changes have a dramatic impact on the downward flux of sediments and as such influence the transportation and fate of suspended sediments. The traditional assumption of suspended sediment being inorganic individual grains for the quantification and modeling of sediment transport is likely to result in erroneous results and management decisions. Flocs settle faster than their individual constituent particles (but orders of magnitude slower than that predicted by Stokes' equation for a similar size), and, for large flocs, can have porosity close to 100% and a corresponding density close to that of water. Flocs are composed of significant living organic components (primarily bacteria) which produce an extracellular polymeric substance (fibrils) which glues particles together giving them greater strength than an electrochemically bound floc, and a pseudo plastic nature. Because of this active living component, flocs should be thought of as micro ecosystems (composed of a matrix of water, inorganic, and organic particles) with autonomous and interactive physical, chemical, and biological functions or behaviors operating within the floc matrix. A better understanding of how floc structure influences floc behavior will help to refine our knowledge and management of suspended sediment transport in a variety of aquatic ecosystems.
Lake Sediments as Records of Past Catchment Response
Authors: Dearing John 
Published: April 2006

AbstractThe sediments that accumulate at the beds of lakes are natural archives of information about catchment processes that extend back far further than instrument records. This article reviews the kinds of questions that long records can address, and summarises the technical and analytical approaches taken. Records of river discharge, sediment delivery, and soil erosion obtained in this way over decades and centuries are increasingly used to understand the behaviour of fluvial systems, especially the combined effects of human activity and climate. Case‐studies now available for different parts of the world can be used to provide the temporal perspective to the current levels of fluvial and erosional processes in human‐dominated landscapes, and together show the strong dependence of sediment delivery on catchment size.
Water Quality Monitoring
Authors: Chapman Deborah V , Meybeck Michel , Peters Norman E 
Published: April 2006

Abstract
Water quality monitoring is the process of gathering data that describes the physical, chemical, and biological condition of a water body. This chapter presents an overview of the processes involved in water quality monitoring and illustrates some of the approaches used with examples of existing monitoring programs. Over the last century, improved understanding of water quality, combined with advances in measurement and monitoring technology have increased the possibility of measuring hundreds of different variables in surface and groundwaters. However, efficient use of resources for monitoring depends on careful selection of objectives for the water quality monitoring program and on targeting variables and monitoring methods that address those objectives. Recent appreciation of the close link between the physical and chemical condition of a water body and its biological component has led to the incorporation of biological approaches in many large‐scale programs to assess surface water quality. Today, monitoring programs take many forms, from measurement of a few specific variables to establish trends or effectiveness of remediation measures, to sophisticated evaluation of toxic impacts of wastewaters, to relatively simple determination of the state of the aquatic environment using citizen participation. Confidence in all data gathered and its resultant usefulness for management and policy development is essential; this can only be achieved by a careful program of quality assurance that extends from sample collection in the field, to analysis in the laboratory, to data handling and manipulation.
Effects of Human Activities on Water Quality
Authors: Peters Norman E , Meybeck Michel , Chapman Deborah V 
Published: April 2006

AbstractWater quality comprises the physical, chemical, and biological characteristics of a water body. The water body acquires these characteristics from a suite of complex interactions among the water, atmosphere, soils, and lithology. Human activities affect both water quality and quantity. Human activities change land use and land cover, which changes the water balance and usually changes the relative importance of processes that control water quality. Furthermore, most human activities generate waste ranging from gases to concentrated radioactive wastes. Although each issue can be subdivided into a myriad of individual processes or activities, the primary water‐quality issues affected by human activities include organic material, trace elements (heavy metals), acidic atmospheric deposition and runoff, salinization, nutrients (primarily nitrogen and phosphorus), pathogenic agents including bacterial pathogens, enteric viruses, and protozoans, suspended sediment, oil and grease, synthetic organic compounds, thermal pollution, exotic and invasive species, pesticides and herbicides, and radioactivity. In addition to the various issues, each human activity has a potential cyclical and cascading effect on water quality and quantity along hydrologic pathways. The degradation of water quality in one part of a watershed can have negative effects on users downstream; the timescale of effects is determined by the residence time of that substance along various hydrological pathways. An extremely important factor is that substances added to the atmosphere, land, and water generally have relatively long timescales for removal or cleanup. The nature of the substance, including its affinity for adhering to soil and its ability to be transformed, affect the mobility and the timescale for the removal of the substance and its effects on water quality, for example, biota.
Water Quality Modeling
Authors: McCutcheon Steven C 
Published: April 2006

Abstract
Water quality forecasts are vital to determining limitations for point source waste loads and diffuse or nonpoint source loads required to meet water quality standards in streams, lakes, and estuaries. Only mechanistic water quality modeling is widely applicable for forecasting. Although surface water quality modeling has a sound interdisciplinary scientific basis, the use of these analysis tools are limited in regulatory and resource decision making by a lack of a professional consensus defining model application protocols. To analyze water quality problems, (i) the uses for a water body must be evaluated, (ii) models must be calibrated and tested to relate impaired water quality to the waste sources, (iii) a formal uncertainty analysis must define a margin of safety to protect human and ecological health, and (iv) when necessary, an economic analysis must be performed to determine if the designated uses are reasonably achievable.
Terrestrial Ecosystems
Authors: Tague Christina L , Band Lawrence E , Franklin Janet 
Published: April 2006

AbstractThe science of ecohydrology centers on understanding the linkages and feedbacks between terrestrial ecosystems and the hydrologic cycle. Within the disciplines of hydrology, ecosystem ecology, and community ecology, a wide range of conceptual, mathematical, and field‐based approaches have evolved to address specific ecohydrologic research questions. In this article, we discuss key elements of these ecohydrologic approaches. We begin by focusing on conceptual frameworks that are organized at the patch level, which define spatially homogeneous units. We compare a set of models in terms of the specific hydrologic and ecologic processes considered and the degree of coupling between them. We then address issues of landscape heterogeneity and compare approaches to the resolution of spatial patterns of soil, topography, vegetation, and atmospheric conditions and the representation of the interactions and feedbacks between neighboring patches. The hierarchical structure and function of terrestrial ecohydrologic systems involve processes varying over very different time and space scales. Finally, we discuss challenges and next steps in developing an integrated framework that can address the range of spatial and temporal scales implied by hydrologic feedbacks on both shorter‐term ecosystem material and energy cycling and longer‐term ecosystem structure and evolution.
Subsurface Stormflow
Authors: Weiler Markus , McDonnell Jeffrey J , Tromp‐van Meerveld Ilja , Uchida Taro 
Published: April 2006

Abstract
Subsurface stormflow is a runoff producing mechanism operating in most upland terrains. In a humid environment and steep terrain with conductive soils, subsurface stormflow may be the main mechanism of storm runoff generation. In drier climates and in lowlands with gentler topography, subsurface stormflow may occur only under certain extreme conditions (high antecedent soil moisture), when transient water tables form and induce lateral flow to the channel. While an important contributor to the volume of flow in the stream, subsurface stormflow is also responsible for the transport of labile nutrients into surface water bodies. Since the flow path of water in the subsurface often determines the chemistry of waters discharging into the stream and hence the water quality, characterizing this subsurface flow path and the water's age and origin is important. Subsurface stormflow may also enhance positive pore pressure development in steep terrain and may be responsible for landslide initiation. Thus, subsurface stormflow is of great interest and importance beyond the conventional hydrological literature. This article examines the history of the study of subsurface stormflow processes, reviews theories on the generation of subsurface stormflow, and gives a detailed overview of current research in subsurface flow processes and the implication for future research.
Flood Routing and Inundation Prediction
Authors: Bates Paul D 
Published: April 2006

Abstract
This contribution considers the methods available to hydrologists to simulate flow routing and inundation in natural channels. Whilst the fluid dynamics of free surface flow in rivers and over floodplains may be complex, the methods available to treat such problems range widely in complexity from simple empirical models to full solutions of three‐dimensional Navier–Stokes equations with sophisticated representations of flow turbulence. These methods are reviewed in detail, followed by a consideration of their requirements for topography, friction, initial condition, boundary condition, and validation data. In particular, the contribution discusses how these needs are being met increasingly using remote sensing techniques. Lastly, the contribution considers techniques to evaluate uncertainties in flow modeling.
Aquifer Characterization by Geophysical Methods
Authors: Vereecken Harry , Kemna Andreas , Münch Hans‐Martin , Tillmann Axel , Verweerd Arre 
Published: April 2006

AbstractGeophysical methods are increasingly being used to characterize the subsurface. They offer the potential to derive basic characteristics, state variables, and properties of geological formations. In this article, we focus on the application of geophysical methods to derive properties and state variables of aquifer systems. Special attention is given to the assessment of hydraulic conductivity, porosity, and water saturation. Three different groups of methods (seismics, electrical techniques, and electromagnetics) and their combined use are discussed. For each method, relationships between geophysical and hydrogeological quantities are outlined and applications are presented. A separate section is devoted to the development and application of combined approaches in hydrogeophysics.
Hydrology of Snowcovered Basins
Authors: Davison Bruce , Pietroniro Alain 
Published: April 2006

AbstractSnowcovered catchments are an integral part of the earth's physical, chemical, and biological regulatory processes. Catchment‐based assessments of snow are typically derived from snow surveys and snow courses. Remote sensing is also a valuable tool for use in understanding the nature and distribution of snowcover in a catchment. Snowcovered basin classifications are founded on the source and timing of runoff and the characteristics of the snow. In order to understand the hydrology of snowcovered catchments, it is important to understand the physics of snowmelt and other related phenomena, such as canopy effects that influence the temporal and spatial distribution of snow within a catchment, including both the energy and mass balance components. Operational temperature index models for basin snowmelt and statistical models for horizontal snowcover distribution help approximate some of the physical processes that are not (or cannot be) directly measured. Hydrological models are an attempt to articulate an understanding of the complex and nonlinear interactions within the hydrological cycle using a rational mathematical approach such as an index method or the energy balance approach. A number of projects have been completed or are underway to compare these models. Hydrological applications, avalanche forecasting, weather forecasting, and climate modeling have all driven snow research, with much cross fertilization between these fields.
Surface and Englacial Drainage of Glaciers and Ice Sheets
Authors: Nienow Peter , Hubbard Bryn 
Published: April 2006

AbstractSupraglacial drainage occurs wherever snowpack, firn, or ice at the glacier surface is at the pressure melting point and supplied with additional energy, thereby generating melt water. Energy sources vary, but net radiation is usually the dominant source, although inputs of rainwater can also provide large volumes of surface runoff. The surface melt water is routed through the snowpack, firn, and across the glacier surface according to the local hydraulic gradient. In general, routing of water through snow and firn is slow (10−4–10−5 m s−1), contributing to a significant lag between melt water production and runoff at the glacier snout, whereas flow across exposed ice surfaces is typically 3–5 orders of magnitude faster. Under certain conditions where parts of the snowpack, firn, and/or ice surface are below the pressure melting point, the melt water will refreeze. Otherwise, the melt water will be routed supraglacially to the glacier margin unless intersected by a pathway from the glacier surface to the glacier interior. Such pathways include crevasses and moulins, and in temperate glaciers, microscale englacial veins. Flow rates through the englacial system vary considerably according to the hydraulic efficiency of the route taken. The routing of melt waters through both supraglacial and englacial drainage systems therefore affects the runoff response of an ice mass to rain and melt water inputs. During the course of a melt season, the efficiency of routing through both systems evolves, thereby altering the runoff response time to input variations.