bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Flood Simulation
Authors: Stelling Guus S , Verwey Adri 
Published: April 2006

Abstract
This contribution describes the state of the art of numerical flood simulation, in particular, the models based upon hydraulic laws. Both theory and practical aspects are discussed. In the introduction, various types of applications of these models are listed with their requirements in terms of robustness, accuracy, speed of operation, and engineering staff time. After introducing the 1D Saint Venant unsteady flow equations and describing the meaning of their terms, the concepts of kinematic and diffusive wave approximations are discussed. These provide better ways of understanding the physical behavior of flood waves and demonstrate the link between hydraulic and hydrologic flood propagation models. Numerical discretization of the unsteady flow equations is introduced with special attention given to the correct and robust modeling of rapidly varying flow, as occurring around hydraulic structures, discontinuities in channel beds, and flood‐generating breaches of river embankments and reservoir dams. Proceeding with the 2D flow description and its numerical discretization principles, the emergence of hybrid 1D/2D models is discussed with their different options of linking model components of flood‐prone areas. The quality of models also relies very much on the availability of detailed and correct data. This contribution briefly introduces the impact of new data collection techniques on numerical flood model schematization.
Global Energy and Water Balances
Authors: Ohmura Atsumu 
Published: April 2006

AbstractThe earth's energy and water balances are summarised with the most recent observational and computational results. A special reference is given to the earth's surface. After a brief discussion of the limits of the observational accuracy, the author explains the mean state of the energy balance starting with the sun, through the atmosphere and to the earth's surface. The main contents are the Total Solar Irradiance (earlier called solar constant) and its variability, the climatic effect of the earth's orbital change, extinction processes of solar radiation in the atmosphere, the distributions of solar radiation on the earth's surface, reflection and albedo, terrestrial radiation from the atmosphere and the earth's surface, net radiation, sensible and latent heat fluxes, subsurface heat flux, and latent heat of melt. The distributions of the individual components are presented in maps. The important points of geographical distributions and energy fluxes are explained in the text. The energy balance climatology in the present article differs from earlier works mainly on three topics: 1) larger atmospheric absorption of solar radiation; 2) smaller solar radiation on the earth's surface; and 3) larger terrestrial counter radiation. These new situations are the results of the recent advances in spectrometry, observational technology both on the earth's surface and in the space, and also in computational skill. Therefore, the historical development of the understanding of the earth's energy balance is added. The article ends with a brief description of the mean hydrological cycle, allowing unsteady conditions due to the melt of glaciers during the twentieth century.
Precipitation Measurement: Gauge Deployment
Authors: Robinson Mark 
Published: April 2006

Abstract
The deployment of a network of rain gauges involves two stages: first, the broad distribution of gauges across a region or catchment and, second, the specific location of each gauge. The spatial distribution of gauges across a region will be determined by a combination of: (a) physical characteristics of the region, including the topography and the natural variability of precipitation, and (b) institutional factors, such as the purpose of the network (setting the accuracy and level of detail of data required as well as the resources available). The specific location of gauges will be determined by purely local factors, which would affect the accuracy of the measurements. These are primarily concerned with site exposure and wind effects that could lead to errors in catch and make the data unrepresentative of a larger area.
Evaporation Measurement
Authors: Verhoef Anne , Campbell Claire L 
Published: April 2006

Abstract

This chapter summarises the practical methods available to estimate evaporation,
E
. It describes the background of methods based on soil physical, micrometeorological and plant physiological concepts. The most appropriate method will mainly depend on required spatial and temporal scales of
E
, accuracy needed, and the available resources (financial and manpower). These issues are taken into account during the discussion.
Actual Evaporation
Authors: Dolman Albertus Johannes 
Published: April 2006

AbstractActual evaporation concerns the evaporation from natural surfaces. Globally actual evaporation from the land amounts to around 71 103 km3year−1. Measurement of evaporation occurs by water balance techniques or directly through micrometeorological techniques. Actual evaporation depends on land cover and meteorological conditions. Evaporation can be predicted by various equations, amongst the Penman‐Monteith equation which takes into account both the vegetation properties as well as the meteorological conditions. In the case of sparsely vegetated areas soil evaporation and plant evaporation need to be treated separately. Estimating the correct value of surface conductance is a critical issue in applying the Penman‐Monteith equation, but models exists. Evaporation from bare soil can be treated as a two stage process, with rapid evaporation at potential rates after rain, and subsequent drying. At larger than catchment scales, feedbacks with the atmospheric boundary layer make it possible to apply evaporation equations based on equilibrium concepts, such as the Priestley‐Taylor equation. There has been substantial progress in evaporation modeling and measurements over the last 25 years. This knowledge can be used much more in assessing changes in evaporation of catchments that may result from perturbations in land use and climate.
Satellite‐Based Estimation of Precipitation Using Microwave Sensors
Authors: Huffman George J 
Published: April 2006

Abstract
Satellite‐borne sensors provide critical input to estimating precipitation over the vast majority of the Earth's surface that lacks adequate in situ observing systems. This article reviews the legacy of sensors, satellites, and data archives that have accrued throughout the Space Age, and that largely governs the precipitation estimates that are available to the hydrological community, both currently and over the long term. Tables of publicly available, quasi‐global, satellite‐based precipitation data sets are introduced, examples are provided, data quality is considered, and future prospects are outlined. One major theme throughout the article is to raise the key issues that users should consider in determining whether a particular set of precipitation estimates is appropriate for their particular application.
Land‐Cover Classification and Change Detection
Authors: Hansen Matthew C , Goetz Scott J 
Published: April 2006

AbstractVarious multispectral data sets and tools are available for mapping land cover and land‐cover change for inputs to hydrologic applications. The best choice is often a function of the specific application. New sensors offer increased capability in mapping spatial detail and temporal variation of land‐cover categories. Algorithms have advanced in robustness and include distribution‐free methods that are superior to traditional approaches in terms of modeling the multispectral distributions of reference data. Advanced subpixel methods of mapping land cover offer greater thematic coherency and the possibility of using consecutive land‐cover characterizations to map change. The success of deriving a meaningful result, such as deriving a relationship between aquatic biotic indices and land‐cover change, relies on a high‐quality land‐cover reference map. By choosing the most appropriate data sources, constructing a defensible land‐cover definition set, and employing robust algorithms, analysts allow for the meaningful incorporation of land‐cover map information into hydrological studies.
Estimation of Glaciers and Sea‐Ice Extent and their Properties
Authors: Stroeve Julienne , Long David , Comiso Josefino C , Scambos Ted A , Shuman Chris A 
Published: April 2006

AbstractPast satellite missions have demonstrated the utility of spaceborne remote sensing in studies of polar ice. Because of their ability to “see” into polar ice without regard to cloud cover or solar lighting, microwave remote sensing instruments have played and will continue to play an increasing role in such studies and in long‐term monitoring the polar regions. Microwave sensors can be either active radars which transmit and receive, or receive‐only radiometers. Spaceborne microwave sensors such as radiometers and scatterometers offer wide‐area, frequent coverage but at lower resolution and a longer historical database. The historic data sets are particularly important since they provide a baseline for studies of global change. Synthetic aperture radar systems possess high resolution capability but have restricted spatial and temporal coverage. Microwave sensors are sensitive to snow and ice structure and are particularly sensitive to freeze/thaw conditions. Optical sensors can also be active (Lidars) or passive. Laser altimeters are an example of an active optical sensor. They provide accurate ice sheet topography information. Passive optical sensing is useful in change detection and infrared ice temperature sensing. In this chapter, essential background in microwave and optical remote sensing of sea‐ice, glaciers and ice sheets is provided, along with application examples.
Hydrology of Swelling Clay Soils
Authors: Smiles David , Raats Peter A C 
Published: April 2006

AbstractTheory of water flow in nonswelling soils has been used for more than 50 years but liquid flow in porous media that change volume with liquid content is not well established in soil science, although it is considered increasingly in chemical and mining engineering and in soil mechanics. Theory of water flow in swelling systems must satisfy material continuity; it must also account for changes in the gravitational potential energy of the system during swelling and for anisotropic stresses that constrain the soil laterally but permit vertical movement. A macroscopic, phenomenological analysis based on Darcy's law provides a useful first approach to the hydrology of such soils and, if we presume that volume change, in the large, is essentially one‐dimensional, material coordinates based on the vertical distribution of the solid phase result in a water flow equation analogous to the Richards equation for nonswelling soils. This framework fully accounts for the vertical strain of the solid phase, and solutions to the flow equation are available for a wide range of practically important initial and boundary conditions. The approach has been well tested in clay suspensions and in saturated systems such as mine tailings and sediments. It is also applied in soil mechanics and, here, we apply it to swelling soils. As with the use of the Richards equation in rigid soils, we recognize that complications arise, but the approach remains the most coherent and profitable to support current needs and serve as a point of departure for future research. The use of material coordinates is simple. We discuss some experimental difficulties in using the approach and also consider extension of the approach to more than one dimension.
Water Movement in Hydrophobic Soils
Authors: Doerr Stefan H , Ritsema Coen J 
Published: April 2006

AbstractHydrophobicity (water repellency) can reduce the affinity for soils to water such that infiltration or wetting may be delayed for periods ranging from as little as a few seconds to in excess of weeks. Soil hydrophobicity is thought to be caused primarily by a coating of long‐chained hydrophobic organic molecules on individual soil particles. These substances may be released from a range of plants, decaying organic matter, soil fauna, and microorganisms either naturally or during burning. Hydrophobicity tends to be spatially and temporally highly variable, which makes its effects difficult to observe and predict. It is often most prominent after prolonged dry spells and usually disappears after prolonged contact with water. Owing to the cultivation of certain frequently introduced plant species and the increase in wildfires in some regions, hydrophobicity has developed in previously unaffected areas. Amongst its effects are inhibited plant growth, increased overland flow and soil erosion, uneven spatial and vertical wetting patterns, reduced evaporation, and enhanced risk of groundwater contamination associated with enhanced preferential flow. Recent modeling approaches have been successful in predicting the effects of hydrophobicity on soil water movement at plot or small‐field scales, however, approaches to predict in detail its hydrological effects at larger scales are yet to be developed.
Transpiration and Root Water Uptake
Authors: de Willigen Peter , Heinen Marius , Kirkham Mary Beth 
Published: April 2006

AbstractRoot water uptake is one of the major components of the water balance of a soil. In this article, both the physical as well as the physiological aspects of root water uptake and transpiration are dealt with. The regulation of transpiration by different mechanisms on different levels (e.g. through hormones, adaptation of vessel diameter, root radius, and vertical extension of the root system) is discussed. Attention is paid to the modeling of water uptake by single roots and root systems. The last section deals with the different techniques used to measure root water uptake, for example, lysimeter, sap flow, inverse modeling, and discusses the advantages and disadvantages of the different methods.
Measuring Soil Water Content
Authors: Topp G Clarke , Ferré Ty PA 
Published: April 2006

Abstract
Major advances in the measurement of soil water content have arisen from electromagnetic (EM) methods that have developed rapidly in the last 20 years. Estimates of water content from EM measurements make use of the large relative permittivity of water compared to other soil components. Time domain reflectometry (TDR) and capacitance approaches use “probes” that convey signal into the soil and thus can measure principally the upper one‐meter depth. Ground penetrating radar (GPR) using noninvasive, transmitting, and receiving antennae possesses the capability to measure to even greater depths without causing soil disturbance. Remote radar and passive microwave methods, operating generally above 1 GHz, derive their information from within a few centimeters of the ground surface. Thermogravimetric and neutron moderation continue as viable long‐standing methods but are being used less as these methods are not amenable to data‐logging. The variety of instruments has increased the surface and near‐surface soil water measurement capabilities. Now it is possible for hydrologists to make informed choices among methods, and it is important to do so to optimize their study results.
Soil Water Potential Measurement
Authors: Durner Wolfgang , Or Dani 
Published: April 2006

AbstractSoil water potential controls the dynamics of water in soils. This article describes methods to measure soil water potential. Available methods differ with respect to the moisture range where they are applicable. In the moist range, the pore water pressure of the soil is directly measured with tensiometers. In the intermediate moisture range, reference porous media are suitable, where the water saturation changes with water potential. Gypsum blocks, granular matrix sensors, heat dissipation matric potential sensors, and filter paper are used. If embedded in the soil and in hydraulic equilibrium with it, soil water potential is obtained by a calibration relationship from a water content dependent measurement in the reference porous medium. In relatively dry soils, water potential is derived from vapor pressure measurements by thermocouple psychrometry. This article presents the theoretical background of the various measurement techniques and illustrates the construction principles of measuring instruments. Problems and pitfalls of water potential measurements, in particular with tensiometers, are discussed. A list of manufacturers of water potential measurement instruments is given at the end of the article and a reference list provides material for further background information.
Measuring Sediment Loads, Yields, and Source Tracing
Authors: Leeks Graham 
Published: April 2006

Abstract
The sediment load of rivers is, for both practical purposes and field research, usually divided into the finer suspended load and coarser bed load. A range of instruments can be used, depending on the mode of sediment transport. Measurements of the bed load can be made using fixed and portable traps, samplers and tagging methods, and electronic detection systems. Suspended sediment load is usually measured with both manual and automatic samplers. Continuous measurements are made possible by using turbidity as a surrogate measure of suspended sediment concentrations. An advantage in the use of the manual and automatic samplers is to provide samples which can be subjected to further analysis (e.g. of particle size distributions or chemistry). One of the opportunities this can provide is to identify up‐catchment sediment sources, including channel, gully, sheet/rill, and surface erosion under different land uses. Source “fingerprints” are identified from combinations of sediment properties. Multivariate analysis and mixing models can then be used to quantify the relative contributions from individual sources.
On the Worldwide Riverine Transport of Sediment – Associated Contaminants to the Ocean
Authors: Swarzenski Peter W , Campbell Pamela L 
Published: April 2006

Abstract
The continuous and persistent weathering of the continents and the ensuing transport of both eroded and anthropogenic products by rivers account for almost all the dissolved solutes, particulates, and sediment‐associated contaminants delivered to the ocean. Transported within this riverine load are essential nutrients (e.g. P, N, C), (oxy)hydroxides of Fe/Mn that act as highly efficient riverine scavengers, an ever‐changing suite of man‐made organic and inorganic constituents, as well as a wide variety of natural solutes (e.g. Si, Ca, Mg, Sr). The environmental behavior of these river‐borne constituents is controlled by dynamic phase partitioning between operationally defined dissolved, colloidal, and particulate pools control. As most trace elements are bound onto river particulates, their fate is defined foremost by the nonconservative nature of such solids as they move along the particle‐size continuum or are exchanged and remobilized in river bed and floodplain sediments. This paper describes the global riverine transport of sediment‐associated contaminants to the ocean.
Acidic Deposition: Sources and Effects
Authors: Driscoll Charles T , Fallon‐Lambert Kathy , Chen Limin 
Published: April 2006

Abstract

Acidic deposition delivers acids and acidifying compounds to the Earth's surface, which are then transported through soil, vegetation, and surface waters and, in turn, set off a cascade of adverse ecological effects. Acidic deposition has altered forest soil by accelerating the leaching of available base cations, enhancing the accumulation of sulfur and nitrogen, and increasing the concentration of dissolved inorganic aluminum in soil waters. Soils that are compromised by acidic deposition are less able to neutralize additional amounts of acidic deposition, and provide poorer growing conditions for plants. Acidic deposition has impaired the surface water quality by lowering pH, decreasing
acid‐neutralizing capacity
(
ANC
), and increasing concentrations of dissolved inorganic aluminum. These changes have reduced the species diversity and abundance of aquatic life. Regulatory controls initiated in Europe and North America over the last three decades have decreased emissions of sulfur dioxide and to a lesser extent nitrogen oxides. Emission reductions have resulted in widespread decreases in concentrations of sulfate in surface waters, with some waters showing an increase in ANC. Given the loss of acid‐neutralizing base cations and the accumulation of sulfur and nitrogen in soil, many ecosystems have become more sensitive to additional acidic deposition and recovery will likely be delayed. Long‐term research shows that deeper emissions cuts will lead to greater and faster recovery from acidic deposition in impacted regions.
Nutrient Cycling
Authors: Edwards Anthony C , Wetzel Robert G 
Published: April 2006

AbstractNutrient concentrations within aquatic ecosystems have increased markedly during the last fifty years due to a variety of causes. Significant changes to the rates of nutrient cycling, particularly of nitrogen and phosphorus, have influenced their biological availability on a global scale. Three broad groupings of processes that directly influence nutrient cycling within freshwaters are described. Retention modifies the availability of nutrients for transport, while selectivity between individual chemical species results in preferential uptake and/or transport, and finally transformation processes alter the physical state or reactivity of particular nutrients. Differences in spatial and temporal dynamics of delivery and transport mechanisms among individual nutrients have caused variable relative changes in nitrogen and phosphorus concentrations and fluxes. These composite dynamic factors make it difficult to couple causal relationships between nutrient sources and their impacts.
Urban Water Quality
Authors: Ellis J Bryan , Marsalek Jiri , Chocat Bernard 
Published: April 2006

AbstractSteady growth of population, due to overall population increases and continuing migration from rural to urban areas, creates enormous demands and stresses on urban waters with respect to water supply, drainage, flood protection, wastewater management, and beneficial uses of receiving waters and groundwater. Urban water issues are therefore in the forefront of water management priorities in practically all regions of the world, though often for broadly varying reasons. Key issues of urban water management are discussed in this article, which focuses on the evolution of urban drainage infrastructure, characterization of urban drainage, urban runoff impacts on receiving waters, urban drainage management, water, and wastewater reuse and future perspectives and priorities. The discussion focuses on the collection and transport of urban effluents (sewer systems), characterization of urban drainage provided by combined or storm sewers (flows and their quality), impacts of urban drainage effluents on receiving waters, and groundwater and impact mitigation by integrated urban drainage management with the emphasis placed on the management of surface runoff and water/wastewater reuse. While the progress in integrated engineering science, watershed‐based management and new water technologies is impressive, the challenges of maintaining and improving urban water services, particularly in low‐income countries, are formidable and may be further exacerbated by demographic, social, and climate change.