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This study examines a selection of river confluences, places that are frequently locations of important physical investigations by hydrologists, geomorphologists, biologists, and engineers, among others. In contrast, confluences can also demonstrate a complex interplay of historical, economic, social, and political factors. Many urban stream confluences were sites of prehistoric human settlement; others are more recent historic sites, or important shipping facilities; and some are simply tourist attractions. From the multitude of stream confluences, this paper examines a small selection from the United States of America and Europe, with a focus on the multiplicity of human associations and layers of meaning. [ABSTRACT FROM AUTHOR]

Annual streamflows have decreased across mountain watersheds in the Pacific Northwest of the United States over the last ~70 years; however, in some watersheds, observed annual flows have increased. Physically based models are useful tools to reveal the combined effects of climate and vegetation on long-term water balances by explicitly simulating the internal watershed hydrological fluxes that affect discharge. We used the physically based Simultaneous Heat and Water (SHAW) model to simulate the inter-annual hydrological dynamics of a 4 km2 watershed in northern Idaho. The model simulates seasonal and annual water balance components including evaporation, transpiration, storage changes, deep drainage, and trends in streamflow. Independent measurements were used to parameterize the model, including forest transpiration, stomatal feedback to vapour pressure, forest properties (height, leaf area index, and biomass), soil properties, soil moisture, snow depth, and snow water equivalent. No calibrations were applied to fit the simulated streamflow to observations. The model reasonably simulated the annual runoff variations during the evaluation period from water year 2004 to 2009, which verified the ability of SHAW to simulate the water budget in this small watershed. The simulations indicated that inter-annual variations in streamflow were driven by variations in precipitation and soil water storage. One key parameterization issue was leaf area index, which strongly influenced interception across the catchment. This approach appears promising to help elucidate the mechanisms responsible for hydrological trends and variations resulting from climate and vegetation changes on small watersheds in the region. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The objective of this study is to produce an observationally based monthly evapotranspiration (ET) product using the simple water balance equation across the conterminous United States (CONUS). We adopted the best quality ground and satellite-based observations of the water budget components, i.e., precipitation, runoff, and water storage change, while ET is computed as the residual. Precipitation data are provided by the bias-corrected PRISM observation-based precipitation data set, while runoff comes from observed monthly streamflow values at 592 USGS stream gauging stations that have been screened by strict quality controls. We developed a land surface model-based downscaling approach to disaggregate the monthly GRACE equivalent water thickness data to daily, 0.125° values. The derived ET computed as the residual from the water balance equation is evaluated against three sets of existing ET products. The similar spatial patterns and small differences between the reconstructed ET in this study and the other three products show the reliability of the observationally based approach. The new ET product and the disaggregated GRACE data provide a unique, important hydro-meteorological data set that can be used to evaluate the other ET products as a benchmark data set, assess recent hydrological and climatological changes, and terrestrial water and energy cycle dynamics across the CONUS. These products will also be valuable for studies and applications in drought assessment, water resources management, and climate change evaluation. [ABSTRACT FROM AUTHOR]

Cities across the world have had to diversify and expand their water supply systems in response to demand growth, groundwater depletion and pollution, and instability and inadequacy of regional surface freshwater sources. In the U.S., these problems plague not only the arid Western cities but increasingly also cities in the Eastern portions of the country. Although cities continue to seek out new sources of water via Promethean projects of long-distance supply systems, desalinization plants, and the recharge of aquifers with surface water, they also pursue water conservation because of its low cost and other benefits. We examine water conservation as a complex sociotechnical system comprising interactions of political, sociodemographic, economic, and hydroclimatological factors. We provide quantitative data on the factors that affect more and less advanced transitions in water conservation regimes, and we show that water stress and other hydrological data can only partially predict the transition. We also provide qualitative case studies to identify institutional and political barriers to more advanced water conservation regimes. This interdisciplinary, mixed methods approach typifies the need for knowledge that informs hydrologists about how their research may or may not be adopted by decision-makers. [ABSTRACT FROM AUTHOR]

Many challenges currently facing agriculture require long-term data on landscape-scale hydrologie responses to weather, such as from the Goodwater Creek Experimental Watershed (GCEW), located in northeastern Missouri, USA. This watershed is prone to surface runoff despite shallow slopes, as a result of a significant smectitic clay layer 30 to 50 cm deep that restricts downward flow of water and gives rise to a periodic perched water table. This paper is the first in a series that documents the database developed from GCEW. The objectives of this paper are to (i) establish the context of long-term data and the federal infrastructure that provides it, (ii) describe the GCEW/Central Mississippi River Basin (CMRB) establishment and the geophysical and anthropogenic context, (iii) summarize in brief the collected research results published using data from within GCEW, (iv) describe the series of papers this work introduces, and (v) identify knowledge gaps and research needs. The rationale for the collection derives from converging trends in data from long-term research, integration of multiple disciplines, and increasing public awareness of increasingly larger problems. The outcome of those trends includes being selected as the CMRB site in the USDA-ARS Long-Term Agro-Ecosystem Research (LTAR) network. Research needs include quantifying watershed scale fluxes of N, P, K, sediment, and energy, accounting for fluxes involving forest, livestock, and anthropogenic sources, scaling from near-term point-scale results to increasingly long and broad scales, and considering whole-system interactions. This special section informs the scientific community about this database and provides support for its future use in research to solve natural resource problems important to US agricultural, environmental, and science policy. [ABSTRACT FROM AUTHOR]

For two watersheds in the northern Midwest United States, we show that landscape depressions have a significant impact on watershed hydrology and sediment yields and that the Soil and Water Assessment Tool (SWAT) has appropriate features to simulate these depressions. In our SWAT models of the Willow River in Wisconsin and the Sunrise River in Minnesota, we used Pond and Wetland features to capture runoff from about 40% of the area in each watershed. These depressions trapped considerable sediment, yet further reductions in sediment yield were required for calibration and achieved by reducing the Universal Soil Loss Equation (USLE) cropping-practice (P) factor to 0.40 to 0.45. We suggest terminology to describe annual sediment yields at different conceptual spatial scales and show how SWAT output can be partitioned to extract data at each of these scales. These scales range from plot-scale yields calculated with the USLE to watershed-scale yields measured at the outlet. Intermediate scales include field, upland, pre-riverine, and riverine scales, in descending order along the conceptual flow path from plot to outlet. Sediment delivery ratios, when defined as watershed-scale yields as a percentage of plot-scale yields, ranged from 1% for the Willow watershed (717 km²) to 7% for the Sunrise watershed (991 km2). Sediment delivery ratios calculated from published relations based on watershed area alone were about 5 to 6%, closer to pre-riverine-scale yields in our watersheds. [ABSTRACT FROM AUTHOR]

We estimated the biological and economic impacts of climate change on freshwater fisheries in the United States (U.S.). Changes in stream temperatures, flows, and the spatial extent of suitable thermal habitats for fish guilds were modeled for the coterminous U.S. using a range of projected changes in temperature and precipitation caused by increased greenhouse gases (GHGs). Based on modeled shifts in available thermal habitat for fish guilds, we estimated potential economic impacts associated with changes in freshwater recreational fishing using a national-scale economic model of recreational fishing behavior. In general, the spatial distribution of coldwater fisheries is projected to contract, being replaced by warm/cool water and high-thermally tolerant, lower recreational priority (i.e., 'rough') fisheries. Changes in thermal habitat suitability become more pronounced under higher emissions scenarios and at later time periods. Under the highest GHG emissions scenario, by year 2100 habitat for coldwater fisheries is projected to decline by roughly 50 % and be largely confined to mountainous areas in the western U.S. and very limited areas of New England and the Appalachians. The economic model projects a decline in coldwater fishing days ranging from 1.25 million in 2030 to 6.42 million by 2100 and that the total present value of national economic losses to freshwater recreational fishing from 2009 to 2100 could range from $81 million to $6.4 billion, depending on the emissions scenario and the choice of discount rate. [ABSTRACT FROM AUTHOR]

Predictions of daily flows in ungauged streams frequently rely on index gauges, where the timing of the daily flow at the index gauge is assumed to be similar to that in the ungauged stream. When some limited flow measurements are available at the ungauged sites, the strength of correlation between these flows and candidate index gauges can inform the selection of the index gauges. Here the use of the correlation of daily flows to select index gauges is systematically evaluated using a large flow data set from the Ohio River Valley, USA. Then, a novel method is introduced for predicting the strength with which daily flows at different gauges are correlated with daily flow at a completely ungauged site, using the physical characteristics of the ungauged site. The index gauges can then be selected based on these predicted correlations. The analysis indicates that this new method provides a means of identifying index sites that will yield a desired level of accuracy in flow predictions at ungauged locations. The ungauged sites at which sufficient index gauges are not available are also identified, and flow predictions are not calculated for these sites. Using this new method improves the overall accuracy of predicted flows, relative to existing methods. [ABSTRACT FROM AUTHOR]

The prediction of climate effects on terrestrial ecosystems and water resources is one of the major research questions in hydrology. Conceptual water-energy balance models can be used to gain a first order estimate of how long-term average streamflow is changing with a change in water and energy supply. A common framework for investigation of this question is based on the Budyko hypothesis, which links hydrological response to aridity. Recently, Renner et al. (2012) introduced the climate change impact hypothesis (CCUW), which is based on the assumption that the total efficiency of the catchment ecosystem to use the available water and energy for actual evapotranspiration remains constant even under climate changes. Here, we confront the climate sensitivity approaches (the Budyko approach of Roderick and Farquhar, 2011, and the CCUW) with data of more than 400 basins distributed over the continental United States. We first estimate the sensitivity of streamflow to changes in precipitation using long-term average data of the period 1949 to 2003. This provides a hydro-climatic status of the respective basins as well as their expected proportional effect to changes in climate. Next, we test the ability of both approaches to predict climate impacts on streamflow by splitting the data into two periods. We (i) analyse the long-term average changes in hydro-climatology and (ii) derive a statistical classification of potential climate and basin change impacts based on the significance of observed changes in runoff, precipitation and potential evapotranspiration. Then we (iii) use the different climate sensitivity methods to predict the change in streamflow given the observed changes in water and energy supply and (iv) evaluate the predictions by (v) using the statistical classification scheme and (vi) a conceptual approach to separate the impacts of changes in climate from basin characteristics change on streamflow. This allows us to evaluate the observed changes in streamflow as well as to assess the impact of basin changes on the validity of climate sensitivity approaches. The apparent increase of streamflow of the majority of basins in the US is dominated by an increase in precipitation. It is further evident that impacts of changes in basin characteristics appear simultaneously with climate changes. There are coherent spatial patterns with catchments where basin changes compensate for climatic changes being dominant in the western and central parts of the US. A hot spot of basin changes leading to excessive runoff is found within the US Midwest. The impact of basin changes on the prediction is large and can be twice as much as the observed change signal. Although the CCUW and the Budyko approach yield similar predictions for most basins, the data of water-limited basins support the Budyko framework rather than the CCUW approach, which is known to be invalid under limiting climatic conditions. [ABSTRACT FROM AUTHOR]

This paper shows how uncertainty undermines collaborative transboundary groundwater management. Focusing on the Santa Cruz Aquifer, spanning the United States-Mexico border between Arizona and Sonora, the authors describe the uncertainties within the aquifer using interviews and hydrologic studies. We discuss how data requirements and ambiguous interpretations exacerbate these uncertainties, and explain how each country's water-management culture combines with this uncertainty to create contrasting views on groundwater availability and abstraction impacts. As a result, water managers in both countries predict different impacts from pumping and recharge, and each uses that information discursively to support unilateral policies rather than to promote collaborative management. [ABSTRACT FROM AUTHOR]

The hydrologic response of different climate-change emission scenarios for the twenty-first century were evaluated in 14 basins from different hydroclimatic regions across the United States using the Precipitation-Runoff Modeling System (PRMS), a process-based, distributed-parameter watershed model. This study involves four major steps: 1) setup and calibration of the PRMS model in 14 basins across the United States by local U.S. Geological Survey personnel; 2) statistical downscaling of the World Climate Research Programme''s Coupled Model Intercomparison Project phase 3 climate-change emission scenarios to create PRMS input files that reflect these emission scenarios; 3) run PRMS for the climate-change emission scenarios for the 14 basins; and 4) evaluation of the PRMS output. This paper presents an overview of this project, details of the methodology, results from the 14 basin simulations, and interpretation of these results. A key finding is that the hydrological response of the different geographical regions of the United States to potential climate change may be very different, depending on the dominant physical processes of that particular region. Also considered is the tremendous amount of uncertainty present in the climate emission scenarios and how this uncertainty propagates through the hydrologic simulations. This paper concludes with a discussion of the lessons learned and potential for future work. [ABSTRACT FROM AUTHOR]

We assessed methylmercury (MeHg) concentrations across multiple ecological scales in the Edisto (South Carolina) and Upper Hudson (New York) River basins. Out-of-channel wetland/floodplain environments were primary sources of filtered MeHg (F-MeHg) to the stream habitat in both systems. Shallow, open-water areas in both basins exhibited low F-MeHg concentrations and decreasing F-MeHg mass flux. Downstream increases in out-of-channel wetlands/flood-plains and the absence of impoundments result in high MeHg throughout the Edisto. Despite substantial wetlands coverage and elevated F-MeHg concentrations at the headwater margins, numerous impoundments on primary stream channels favor spatial variability and lower F-MeHg concentrations in the Upper Hudson. The results indicated that, even in geographically, climatically, and ecologically diverse streams, production in wetland/floodplain areas, hydrologic transport to the stream aquatic environment, and conservative/nonconservative attenuation processes in open water areas are fundamental controls on dissolved MeHg concentrations and, by extension, MeHg availability for potential biotic uptake. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the conflicting controls in lake- and river-water hydrogen and oxygen isotopic values in the western U.S. The study uses examines the seasonal distribution of evaporation, precipitation, and snowmelt throughout a range of seasonality regimes. Result shows that the spring snowmelt dispels the landscape through streams and rivers, which results to the depletion of stream and river-water isotopic values.

This article discusses research wherein records of environmental history were analyzed to create a modeled recreation of hydrological processes within the colonial U.S. The study intended to elucidate how water resources historically shaped patterns of human settlement and networks of economic and biological exchange, as well as how present generations may best prepare for future hydrological changes. Researchers hosted by the Massachusetts Institute for Technology (MIT) analyzed historical data from the Northeastern U.S. hydrologic system between Chesapeake Bay and the St. John River in Maine. The study incorporates a conceptual model as well as a methodological model to establish variables such as land cover change and climate change.

Geographic Information Systems (GIS) and multivariate statistical analyses were used to partition the United States into Human Influenced Water Environmental Classes (HIWECs) for the purpose of determining hydrologically similar units within the conterminous United States. Such a framework could be used to investigate various categories of watersheds throughout the country or to establish observatory sites in variant hydrologies. These HIWECs represent areas that are relatively homogeneous with respect to the human influence variables of land cover, population density, and water use; the climate variables of temperature and precipitation; and the physical variables of slope, bedrock permeability, and soil permeability. These variables combine to characterize hydrologic condition and collectively represent the major hydrologic variability that exists across the U.S. GIS was first used to break each of the variables into low to high ranges. Multivariate statistics were then used to identify and cluster areas that share similar characteristics in multivariate data space. HIWECS can serve as a framework for development of water research and management; observatory sites can be selected to capture variant hydrologies that incorporate the human influence element with the criteria that each type of human-influenced hydrologic condition, or class, be represented. [ABSTRACT FROM AUTHOR]

Opperman, Jeffrey J., Ryan Luster, Bruce A. McKenney, Michael Roberts, and Amanda Wrona Meadows, 2010. Ecologically Functional Floodplains: Connectivity, Flow Regime, and Scale. Journal of the American Water Resources Association (JAWRA) 46(2):211-226. DOI: 10.1111/j.1752-1688.2010.00426.x This paper proposes a conceptual model that captures key attributes of ecologically functional floodplains, encompassing three basic elements: (1) hydrologic connectivity between the river and the floodplain, (2) a variable hydrograph that reflects seasonal precipitation patterns and retains a range of both high and low flow events, and (3) sufficient spatial scale to encompass dynamic processes and for floodplain benefits to accrue to a meaningful level. Although floodplains support high levels of biodiversity and some of the most productive ecosystems on Earth, they are also among the most converted and threatened ecosystems and therefore have recently become the focus of conservation and restoration programs across the United States and globally. These efforts seek to conserve or restore complex, highly variable ecosystems and often must simultaneously address both land and water management. Thus, such efforts must overcome considerable scientific, technical, and socioeconomic challenges. In addition to proposing a scientific conceptual model, this paper also includes three case studies that illustrate methods for addressing these technical and socioeconomic challenges within projects that seek to promote ecologically functional floodplains through river-floodplain reconnection and/or restoration of key components of hydrological variability. [ABSTRACT FROM AUTHOR]

Riparian evapotranspiration (ET) in the Rio Grande Basin in New Mexico, USA is a major component of the hydrological system. Over a period of several years, ET has been measured in selected locations of dense saltcedar and cottonwood vegetation. Riparian vegetation varies in density, species and soil moisture availability, and to obtain accurate measurements, multiple sampling points are needed, making the process costly and impractical. An alternative solution involves using remotely sensed data to estimate ET over large areas. In this study, daily ET values were measured using eddy covariance flux towers installed in areas of saltcedar and cottonwood vegetation. At these sites, remotely sensed satellite data from the National Aeronautics and Space Administration (NASA) Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were used to calculate the albedo, normalized difference vegetation index (NDVI) and surface temperature. A surface energy balance model was used to calculate ET values from the ASTER data, which were available for 7 days in the year. Comparison between the daily ET values of saltcedar and cottonwood measured from the flux towers and calculated from remote sensing resulted in a mean square error (MSE) of 0.16 and 0.37 mm day-1, respectively. The regional map of ET generated from the remote sensing data demonstrated considerable variation in ET, ranging from 0 to 9.8 mm day-1, with a mean of 5.5 mm day-1 and standard deviation of 1.85 mm day-1 (n = 427481 pixels) excluding open water. This was due to variations in plant variety and density, soil type and moisture availability, and the depth to water table. [ABSTRACT FROM AUTHOR]

The article demonstrates the possible usage of stable water isotopes to provide unique information for catchment hydrologists in southwest in the U.S. Primarily, the study reveals that the choice of isotope influence the result of hydrograph separation. In this regard, it presents several hydrograph separations that have observed in rainfall for single runoff event and suggests a new technology capable of simultaneous measurements.

The article presents a study on the concentration-discharge relationships for mineral weathering-derived solutes in 59 catchments in the Hydrologic Benchmark Network (HBN) of the U.S. Geological Survey in the U.S. The researchers have plotted the concentrations of solutes including magnesium, sodium, calcium and liquefied silica in contrast to rapid discharge where they confirmed that their concentrations vary from magnitudes of three to twenty which indicate chemostatic characteristics. A novel chemical and mixing model was introduced by the researchers where it shows that the changes discharge match in the subsurface's saturation depth. It adds that a consistent model in hydrology, chemical weathering and transport is required to understand concentration-discharge relationships.

The article presents a study which examined the development of a field scale vegetative filter strip (VFS) submodel for the Soil and Water Assessment Tool (SWAT) in the U.S. VFS is used as a conservation measure to remove pollutants from agricultural runoff. Under the research, the Vegetative Filter Strip MODel (VFSMOD) was adapted to operate at the field scale by determining the effect of flow concentration from plot scale experiments. Researchers noted that the said model enhances the ability of SWAT to address the effectiveness of VFS at the watershed scale.

The Hydrogeomorphic (HGM) functional assessment method is predicated on the ability of hydrogeomorphic wetland classification and visual assessment of alteration to provide reference standards against which functions in individual wetlands can be evaluated. The effectiveness of this approach was tested by measuring nitrogen cycling functions in forested wetlands in an urbanized region in New Jersey, USA. Fourteen sites represented three HGM classes and were characterized as “least disturbed reference” or “non-reference” based on initial visual assessment. Water table levels and in situ rates of net nitrogen mineralization, net nitrification, and denitrification were measured over one year in each site. Hydrological alterations, resulting in consistently low or flashy water table levels, were not correlated with a priori designations as reference and non-reference. Although the flat-riverine wetland class had lower net nitrification and higher denitrification rates than riverine or mineral flat wetland classes, this difference was attributable to the lack of hydrologically-altered wetlands in the flat-riverine class, and thus more consistently wet conditions. Within all HGM classes, a classification based on the long-term hydrological record that separated sites with “normal,” saturated hydrology from those with “altered,” drier hydrology, clearly distinguished sites with different nitrogen cycling function. Based on these findings, current practices for designating reference standard sites to judge wetland functions, at least in urbanized regions, are ineffective and potentially misleading. At least one year of hydrological monitoring data is suggested to classify wetlands into groups that have different nutrient cycling functions, particularly in urban landscapes. [ABSTRACT FROM AUTHOR]

The article focuses on the research on the effect of global change to hydrologic systems affected by snow. It cites studies in western U.S.A. which suggest the occurrence of hydrologic adjustments to a warming climate since the mid-twentieth century. Meanwhile, the current research uses a physically based hydrologic model to evaluate the effects of systematic changes in precipitation and temperature on snow-affected portions of the global land area based from global climate models. It reveals that climate change is most likely to occur in geographic areas where snowmelt hydrology dominates the water cycle due to its warming climate. Moreover, it compares the current research findings with observations in the western U.S.A.

A field measurement program was undertaken as part NASA's Cold Land Processes Experiment (CLPX). Extensive snowpack and soil measurements were taken at field sites in Colorado over four study periods during the two study years (2002 and 2003). Measurements included snow depth, density, temperature, grain type and size, surface wetness, surface roughness, and canopy cover. Soil moisture measurements were made in the near-surface layer in snow pits. Measurements were taken in the Fraser valley, North Park, and Rabbit Ears Pass areas of Colorado. Sites were chosen to gain a wide representation of snowpack types and physiographies typical of seasonally snow-covered regions of the world. The data have been collected with rigorous protocol to ensure consistency and quality, and they have undergone several levels of quality assurance to produce a high-quality spatial dataset for continued cold lands hydrological research. The dataset is archived at the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado. [ABSTRACT FROM AUTHOR]

The article discusses the mercury (Hg) transport in response to storm from the Adirondck region of New York, USA. It is said that the fluxes of Hg in surface waters are affected by hydrological events, in which Hg transport may influence the bioavailability of the chemical to aquatic biota. It is cited that Hg concentrations were not correlated with dissolved organic carbon (DOC) or total suspended solids (TSS). It is mentioned that the attributes of watershed and storm have a role in Hg transport and bioavailability.

Bivariate F distributions are some of the most popular models for hydrological processes. In this article, a drought application is described by deriving the exact distributions of R=X+Y, U=X Y and W=X/(X+Y) and the corresponding moment properties when X and Y follow the bivariate F distribution. Drought data from the State of Nebraska, USA are used. [ABSTRACT FROM AUTHOR]

Large changes in the hydrology of the western United States have been observed since the mid-twentieth century. These include a reduction in the amount of precipitation arriving as snow, a decline in snowpack at low and midelevations, and a shift toward earlier arrival of both snowmelt and the centroid (center of mass) of streamflows. To project future water supply reliability, it is crucial to obtain a better understanding of the underlying cause or causes for these changes. A regional warming is often posited as the cause of these changes without formal testing of different competitive explanations for the warming. In this study, a rigorous detection and attribution analysis is performed to determine the causes of the late winter/early spring changes in hydrologically relevant temperature variables over mountain ranges of the western United States. Natural internal climate variability, as estimated from two long control climate model simulations, is insufficient to explain the rapid increase in daily minimum and maximum temperatures, the sharp decline in frost days, and the rise in degree-days above 0°C (a simple proxy for temperature-driven snowmelt). These observed changes are also inconsistent with the model-predicted responses to variability in solar irradiance and volcanic activity. The observations are consistent with climate simulations that include the combined effects of anthropogenic greenhouse gases and aerosols. It is found that, for each temperature variable considered, an anthropogenic signal is identifiable in observational fields. The results are robust to uncertainties in model-estimated fingerprints and natural variability noise, to the choice of statistical downscaling method, and to various processing options in the detection and attribution method. [ABSTRACT FROM AUTHOR]

Observations show snowpack has declined across much of the western United States over the period 1950–99. This reduction has important social and economic implications, as water retained in the snowpack from winter storms forms an important part of the hydrological cycle and water supply in the region. A formal model-based detection and attribution (D–A) study of these reductions is performed. The detection variable is the ratio of 1 April snow water equivalent (SWE) to water-year-to-date precipitation (P), chosen to reduce the effect of P variability on the results. Estimates of natural internal climate variability are obtained from 1600 years of two control simulations performed with fully coupled ocean–atmosphere climate models. Estimates of the SWE/P response to anthropogenic greenhouse gases, ozone, and some aerosols are taken from multiple-member ensembles of perturbation experiments run with two models. The D–A shows the observations and anthropogenically forced models have greater SWE/P reductions than can be explained by natural internal climate variability alone. Model-estimated effects of changes in solar and volcanic forcing likewise do not explain the SWE/P reductions. The mean model estimate is that about half of the SWE/P reductions observed in the west from 1950 to 1999 are the result of climate changes forced by anthropogenic greenhouse gases, ozone, and aerosols. [ABSTRACT FROM AUTHOR]

A space-filling algorithm (SFA) based on 2D spectral estimation techniques was developed to extrapolate the spatial domain of the narrow-swath near-instantaneous rain-rate estimates from Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) and TRMM Microwave Imager (TMI) using thermal infrared imagery (Meteosat-5) without making use of calibration or statistical fitting. A comparison against rain gauge observations and the original PR 2A25 and TMI 2A12 estimates in the central Himalayas during the monsoon season (June–September) over a 3-yr period of 1999–2001 was conducted to assess the algorithm’s performance. Evaluation over the continental United States was conducted against the NCEP stage IV combined radar and gauge analysis for selected events. Overall, the extrapolated PR and TMI rainfall fields derived using SFA exhibit skill comparable to the original TRMM estimates. The results indicate that probability of detection and threat scores of the reconstructed products are significantly better than the original PR data at high-elevation stations (>2000 m) on mountain ridges, and specifically for rainfall rates exceeding 2–5 mm h-1 and for afternoon convection. For low-elevation stations located in steep narrow valleys, the performance varies from year to year and deteriorates strongly for light rainfall (false alarm rates significantly increase). A preliminary comparison with other satellite products (e.g., 3B42, a TRMM-adjusted merged infrared-based rainfall product) suggests that integrating this algorithm in currently existing operational multisensor algorithms has the potential to improve significantly spatial resolution, texture, and detection of rainfall, especially in mountainous regions, which present some of the greatest challenges in precipitation retrieval from satellites over land, and for hydrological operations during extreme events. [ABSTRACT FROM AUTHOR]

The article looks at the possibility of improvement of weather prediction through terrestrial and atmospheric water dynamics. It highlights the junior faculty and early career scientist forum held at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. Questions raised during the forum include simplifications commonly made when coupling hydrological and atmospheric models, the spatial and temporal scales to capture feedback between land surface and atmosphere, and representing and understanding feedback. Furthermore, the authors suggest the development and maintenance of long-term monitoring systems, the need for data consolidation efforts as well as improved standards that allow easy incorporation in widely used land-surface and atmosphere modeling systems.

The hydrologic cycle is treated in this article as an invention that represents and helps structure a particular understanding of water. Ideas about the circulation of water in what is now called the hydrosphere have been discussed for millennia, and quantitative proof of the basic water balance (between evaporation, precipitation, and streamflow) was established by the nineteenth century. However, “the hydrologic cycle” as a distinct entity and the diagrammatic form by which it is typically represented are much more recent products of hydrological discourse. This article describes the gestation of this entity in the English-speaking hydrological tradition and explains how and why it attained a specific form in the United States in the 1930s. This modern hydrologic cycle, it is argued, internalizes the historical and geographical circumstances in which it was formed; namely a northern temperate society in the throes of modern, state-led industrial development. These circumstances, however, no longer pertain to a majority of people, whose experience of water is different from that represented in the standard hydrologic cycle. To the extent that it structures an understanding of water that is increasingly at odds with social and hydrological experience, the modern hydrologic cycle can be considered unsustainable. [ABSTRACT FROM AUTHOR]

Abstract: The US Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) has developed NRCS GeoHydro 9x, a new ArcGIS application, to complement the WinTR–20 application and assist USDA field staff, and other government, private, and foreign organizations. WinTR–20 is a storm event hydrologic model used to evaluate impacts of structural and land treatment measures. NRCS GeoHydro 9x, using geographic information systems (GIS) tools and techniques, performs hydrologic modeling on a drainage area to compute its catchments, drainage points, drainage lines, slope, runoff curve number, longest flow path, time of concentration (Tc ), and cross-section details. The application acts as a GIS interface to WinTR–20 by exporting the results of GIS analyses of the drainage area in the input format of WinTR–20. NRCS GeoHydro 9x reinforces the idea that GIS tools and techniques enhance productivity by doing preliminary hydrologic analysis of the drainage area in an objective and accurate manner in a relatively short duration. [Copyright &y& Elsevier]

The article discusses the geomorphic controls and transition zones in the lower Sabine River, Texas and Louisiana. A study is conducted to cover the issues of instream flow science and management to identify geomorphic transition zones. It is said that geologic controls and gross valley morphology play a role as geomorphic controls. It is cited that the transition zones delineate reaches with distinct hydrological characteristics in terms of dam releases and coastal backwater effects, flow patterns, frequency of overbank flow, and channel-floodplain connectivity.

The article discusses the carbon isotope fractionation of dissolved inorganic carbon (DIC). It is said that the fractionation is due to outgassing of carbon dioxide from a headwater stream. The isotopic composition of dissolved inorganic carbon was probed as a tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont in the U.S. It is cited that comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt.

Accurate precipitation data are critical for hydrologic prediction, yet outside the developed world in situ networks are so sparse as to make alternative methods of precipitation estimation essential. Several such alternative precipitation products that would be adequate to drive hydrologic prediction models at regional and global scales are evaluated. As a benchmark, a gridded station-based dataset is used, which is compared with the global 40-yr ECMWF Re-Analysis (ERA-40), and a satellite-based dataset [i.e., the Global Precipitation Climatology Project One-Degree Daily (GPCP 1DD)]. Each dataset, with a common set of other meteorological forcings aside from precipitation, was used to force the Variable Infiltration Capacity (VIC) macroscale hydrology model globally for the 1997–99 period for which the three datasets overlapped. The three precipitation datasets and simulated hydrological variables (i.e., soil moisture, runoff, evapotranspiration, and snow water equivalent) are compared in terms of the implied water balances of the continents, and for prediction of streamflow for nine large river basins. The evaluations are in general agreement with previous but more local evaluations of precipitation products and water balances: the precipitation datasets agree reasonably on the seasonality but less on monthly anomalies. Furthermore, the largest differences in precipitation are in mountainous regions and regions where in situ networks are sparse (such as Africa). Derived runoff is highly sensitive to differences in precipitation forcings. At a global level, all three simulations result in water budgets that are within the range of other water balance climatologies. Although uncertainties in the three datasets preclude an evaluation of which one has the lowest errors, overall ERA-40 is preferred because of its agreement with the station-based dataset in locations where the station density is high, its periodic availability, and its temporal resolution. [ABSTRACT FROM AUTHOR]

The main hydrological and morphological features of the Columbia River mouth area, including its tidal estuary, are discussed. Close attention is given to the characteristics of large-scale hydraulic projects in the river basin as well as to dredging and channel training operations in the river mouth area and to the assessment of the impact of these operations on hydrological and morphological processes. Variations in the regime of river flow after its regulation, processes of dynamic interaction and mixing of river and sea water in the estuary are characterized. Changes of the mouth bar and sea coasts near the Columbia River mouth as a result of construction of stream-training jetties are discussed. [ABSTRACT FROM AUTHOR]

The software program HEC-RAS from the Hydrologic Engineering Center (HEC) of the US Army Corps of Engineers is probably one of the most commonly used methods in the world for computing water surface profiles in rivers. The energy method (one of the four bridge subroutines within HEC-RAS) computes the bridge backwater (the upstream surface increase) by applying standard step calculations five times from the end of the expansion reach up to the beginning of the contraction reach, using two different transition loss coefficients and different reach lengths. The aim of this study was to estimate the backwater in a less cumbersome and practical way, without sacrificing accuracy. A one-step energy method is suggested, based on a comprehensive set of laboratory bridge backwater data from compound channels. The proposed method gives an absolute mean error of 10% when applied to these laboratory data and an absolute mean error of 25% when applied to field data collected by the United States Geological Survey including actual flood profiles through many bridges. [ABSTRACT FROM AUTHOR]

The article provides information about the significance of millimeter-wavelength radar in the U.S. It is stated that such radars bridge an observational gap regarding the Earth's hydrological cycle by detecting clouds and precipitation actions. Here, it highlights the history concerning the developments of the said instrument from the 1960s to the present. It discusses the nature of the existing wavelength radar and the range of applications to which the instrument can be applied. Also, it examines the future plan for advanced applications of millimeter radars as well as new cloud and precipitation research platforms based on higher-frequency radars.

The article reports on reusing treated wastewater to augment existing freshwater supplies in the U.S. To address the growing crisis, it stated that the existing engineering and scientific knowledge base must be enhanced to provide improved input to decision makers. A new joint initiative of the environmental engineering and hydrologic sciences research communities, in collaboration with the National Science Foundation (NSF), is proposing to build a national platform for real-time environmental observations with distributed networked sensing and data mining techniques. INSETS: High-resolution river observations in central California;Distributed sensor networks and environmental....

Spring development of diatoms in Ford Lake, Michigan, USA was markedly different in 2004 from 2005 and 2006. In 2004, diatom biovolume surpassed 15mm3 l−1 but in 2005 and 2006 maximum biovolume was less than 5mm3 l−1. Soluble reactive silica (SRSi) in 2004 fell below 5μM whereas in 2005 and 2006, SRSi remained above 30μM. Taxonomic composition was similar among years and consisted mainly of Asterionella, Cyclotella, Fragilaria, Aulacoseira, and Synedra. Bioassay experiments in 2005 demonstrated that P rather than Si was the element most limiting biomass development. However, P supply rate did not account for the differences among years. Model simulations of Si uptake, washout rates, and sinking implicated hydrologic differences among years as the cause of differential success by diatom populations in April of each year. Bioassay experiments performed after overturn demonstrated that diatoms could grow well in unamended lake water, but they did not flourish in the lake; model simulations implicated sinking losses as the reason. In summer 2006, we performed a selective withdrawal of hypolimnetic water from the outlet dam and weakened density stratification. An Aulacoseira bloom resulted in early to mid-August, depleting SRSi to less than 30μM. The lake, which had been acting as a P source, changed to a P sink during the bloom, and cyanobacteria did not develop as they had in all previous years. Stoichiometric calculations indicate that the net SRSi uptake and the net DP uptake during the induced bloom were consistent with diatom production. [Copyright &y& Elsevier]

Ongoing drought in the Colorado River Basin, unprecedented urban growth in the watershed, and numerical model simulations showing higher temperatures and lower precipitation totals in the future have all combined to heighten interest in drought in this region. In this investigation, we use principal components analysis (PCA) to independently assess the influence of various teleconnections on Basin-wide and sub-regional winter season Palmer Hydrological Drought Index (PHDI) and precipitation variations in the Basin. We find that the Pacific Decadal Oscillation (PDO) explains more variance in PHDI than El Niño-Southern Oscillation (ENSO), the Atlantic Multidecadal Oscillation (AMO), and the planetary temperature combined for the Basin as a whole. When rotated PCA is used to separate the Basin into two regions, the lower portion of the Basin is similar to the Basin as a whole while the upper portion, which contains the high-elevation locations important to hydrologic yield for the watershed, demonstrates poorly defined relationships with the teleconnections. The PHDI for the two portions of the Basin are shown to have been out of synch for much of the twentieth century. In general, teleconnection indices account for 19% of the variance in PHDI leaving large uncertainties in drought forecasting. [ABSTRACT FROM AUTHOR]

The impacts of different spatial resolutions and different data assimilation schemes of the available re-analysis data sets (NCEP/NCAR and ERA-40) on the assessment of drought variability are analysed. Particular attention has been devoted to the analysis of the possible existence of a linear trend in the climatic signal. The long-term aspects of drought over the globe during the last forty years have been evaluated by computing the Standardized Precipitation Index (SPI) on 24-month time scale. The SPI, in fact, seems to be a useful tool for monitoring dry and wet periods on multiple time scales and comparing climatic conditions of areas governed by different hydrological regimes. To unveil possible discrepancies between the analyses carried out with the two data sets, we studied the leading space-time variability of drought by applying the principal component analysis (PCA) to the SPI time series. Results suggest that on the global scale, the two re-analyses agree in their first principal component score, but not in the associated loading: both re-analyses capture a linear trend, though the areas where this feature should be most likely observed are not uniquely identified by the two data sets. Moreover, while the ERA-40 unveils the presence of a weak net "global" trend towards wet conditions, the NCEP/NCAR re-analysis suggests that the areas in the world characterised by positive/negative trends balance to zero. At large regional scale, a good agreement of the results with those obtained from the observations are found for the United Stated, while for the European sector the two re-analyses show remarkable differences both in the first loading and in representing the timing of the wet and dry periods. Also for these areas a linear trend, superposed on other short-term fluctuations, is detectable in the first principal component of the SPI field. [ABSTRACT FROM AUTHOR]

Drainages are important features of semiarid landscapes because they are areas where surface water, groundwater, and terrestrial and aquatic ecosystems converge. Management of these critical ecohydrological systems requires a sound understanding of surface water-groundwater interactions. At the basin- to landscape-scale, drainage density, location, and channel characteristics are formed upon a geomorphic and geologic template that limit where and how surface water-groundwater interactions occur. At smaller scales, semiarid surface water-groundwater interactions exhibit a high degree of temporal and spatial variability that links directly to biogeochemical characteristics and ecosystem dynamics. In this paper, we review key features of interactions in semiarid drainages, and supplement the discussion with new examples from the American southwest. We conclude by presenting a series of alternative conceptual models that describe surface water-groundwater interactions within semiarid drainages and highlight areas for future research. [ABSTRACT FROM AUTHOR]

The practice of removing woody vegetation to enhance water supply in semiarid rangelands in the United States continues to generate considerable interest, even though past research has yielded apparently contradictory results concerning its efficacy. In an attempt to elucidate the factors that determine whether and how woody vegetation removal affects water supply, we analysed the problem using a water balance approach. In our analysis, deep drainage is the water balance component associated with water supply. Because the herbaceous vegetation that replaces the woody plants generally has a shallower effective rooting depth (Rd), the amount of soil water potentially available for transpiration is reduced and more is available for deep drainage. The potential increase in deep drainage can be estimated from the capacity of the soil to store plant-available water (Sc) and may be substantial. Our case study on sagebrush rangeland documents how Rd, and consequently Sc, changed after woody vegetation at the site was removed by burning. Using depth profiles of soil water content and matric potential, we showed that the Rd of the post-fire vegetation was about 140 cm, 60 cm less than that of the pre-fire vegetation, and that this resulted in a potential increase in deep drainage of about 6 cm of water—which in semiarid rangelands is substantial. Historical precipitation patterns indicate that there is nearly always sufficient net precipitation to generate the additional 6 cm of deep drainage at this site. However, in most of the area the soil depth is less than 140 cm, so that transpiration and deep drainage would be unaffected by the vegetation change and the overall water supply enhancement would be much less than 6 cm. These results indicate that the change in S. that may follow woody shrub removal is an important criterion to evaluate sites for vegetation conversion. [ABSTRACT FROM AUTHOR]

In 1997, during the late stages of production of NCEP-NCAR Global Reanalysis (GR), exploration of a regional reanalysis project was suggested by the GR project's Advisory Committee, “particularly if the RDAS [Regional Data Assimilation System] is significantly better than the global reanalysis at capturing the regional hydrological cycle, the diurnal cycle and other important features of weather and climate variability.” Following a 6-yr development and production effort, NCEP's North American Regional Reanalysis (NARR) project was completed in 2004, and data are now available to the scientific community. Along with the use of the NCEP Eta model and its Data Assimilation System (at 32-km-45-layer resolution with 3-hourly output), the hallmarks of the NARR are the incorporation of hourly assimilation of precipitation, which leverages leverages a comprehensive precipitation analysis effort, the use of a recent version of the Noah land surface model, and the use of numerous other datasets that are additional or improved compared to the GR. Following the practice applied to NCEP's GR, the 25-yr NARR retrospective production period (1979-2003) is augmented by the construction and daily execution of a system for near-real-time continuation of the NARR, known as the Regional Climate Data Assimilation System (R-CDAS). Highlights of the NARR results are presented: precipitation over the continental United States (CONUS), which is seen to be very near the ingested analyzed precipitation; fits of tropospheric temperatures and winds to rawinsonde observations; and fits of 2-m temperatures and 10-m winds to surface station observations. The aforementioned fits are compared to those of the NCEP-Department of Energy (DOE) Global Reanalysis (GR2). Not only have the expectations cited above been fully met, but very substantial improvements in the accuracy of temperatures and winds compared to that of GR2 are achieved throughout the troposphere. Finally, the numerous datasets produced are outlined and information is provided on the data archiving and present data availability. [ABSTRACT FROM AUTHOR]

Abstract: A procedure for deseasonalising hydrological time series is presented which is based on applying the normal quantile transform (NQT). The scientific literature recently presented examples of utilisation of the NQT that makes the cumulative distribution function (CDF) of the transformed hydrological variable Gaussian. The technique proposed here assumes that the CDFs of variables that form a seasonal time series are non-stationary and periodic; hence the NQT formulation is allowed to be periodic as well. The year is divided into a number of non-overlapping periods, each one characterised by an individual expression for the NQT. The latter is estimated empirically by applying a robust approach that avoids abrupt changes of the transformation through time. The resulting transformed time series is characterised by a single, stationary CDF which is no longer affected by the periodicity. The proposed technique is applied to deseasonalise hydrographs of mean daily flows observed in Italy and the United States. [Copyright &y& Elsevier]

The Columbia River is a major source of and conduit for Pacific Northwest economic activity, and is one of the more heavily modified rivers in North America. Understanding human and climate‐induced changes in its hydrologic properties is, therefore, vital. Long streamflow records are essential to determining how runoff has changed over time, and Columbia River daily streamflow record at The Dalles began in 1878. To understand and separate anthropogenic and climate effects, however, it is also necessary to have a basin‐scale estimate of virgin or naturalized flow. The United States Geological Survey has calculated a monthly averaged adjusted river flow at The Dalles for 1879–1999 that accounts for the effects of flow regulation. The Bonneville Power Administration has estimated the monthly averaged virgin flow at The Dalles, i.e. the flow in the absence of both flow regulation and irrigation depletion for 1929–89. We have estimated the monthly virgin flow of the Columbia River at The Dalles from records of irrigated area for the missing early years, i.e. for the period 1879–1928. In addition, to allow hindcasting of a virgin flow sediment transport for the system, a daily virgin flow index with realistic higher moments and spectral properties has been calculated. Examination of the virgin flow record shows that climate change since the late 19th century has decreased annual average flow volume by > 7%; irrigation depletion has reduced the flow by another ∼7%. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract The physical factors controlling total mercury (HgT) and methylmercury (MeHg) concentrations in lakes and streams of northeastern USA were assessed in a regional data set containing 693 HgT and 385 corresponding MeHg concentrations in surface waters. Multiple regression models using watershed characteristics and climatic variables explained 38% or less of the variance in HgT and MeHg. Land cover percentages and soil permeability generally provided modest predictive power. Percent wetlands alone explained 19% of the variance in MeHg in streams at low-flow, and it was the only significant (p < 0.02) predictor for MeHg in lakes, albeit explaining only 7% of the variance. When stream discharge was added as a variable it became the dominant predictor for HgT in streams, improving the model r2 from 0.19 to 0.38. Stream discharge improved the MeHg model more modestly, from r2 of 0.25 to 0.33. Methylation efficiency (MeHg/HgT) was modeled well (r2 of 0.78) when a seasonal term was incorporated (sine wave with annual period). Physical models explained 18% of the variance in fish Hg concentrations in 134 lakes and 55% in 20 reservoirs. Our results highlight the important role of seasonality and short-term hydrologic changes to the delivery of Hg to water bodies. [ABSTRACT FROM AUTHOR]

1. Wildfires are often followed by severe, sediment-laden floods in burned catchments. In this study, we documented resistance and resilience of stream insect communities to repeated postfire flash floods in a‘burned stream’. We employed a before-after-control-impact (BACI) design, where communities in comparable reaches of a burned stream and a reference stream were sampled from 2 years before, to 6 years after, a crown wildfire in north-central New Mexico.2. The first 100-year flood following the 1996 Dome wildfire reduced total insect density and taxon richness to near zero in the burned stream. Despite showing low resistance, density returned rapidly to prefire levels because of colonisation by simuliids, chironomids and the mayflyBaetis tricaudatus. In general, taxa that were generalist feeders (collectors) with strong larval dispersal dominated communities in early postfire years with repeated, moderate flash floods.3. Taxon richness and community composition were less resilient to postfire hydrologic disturbances. Taxon richness did not recover until floods dampened 4 years after the fire. Despite hydrologic recovery, composition in the burned stream still differed from prefire and reference stream compositions after 6 years postfire. A unique assemblage, dominated by taxa with strong larval or adult dispersal, was established after flash floods abated. Specialist feeders (shredders and grazers) that were common in prefire years were reduced or absent in the postfire assemblage.4. Community succession in the burned stream was explained by the interaction between species traits, geographic barriers to colonisation and hydrologic conditions after the fire. Comparable changes in insect density, taxon richness, community composition and trait representation were not found in the reference stream, providing strong evidence that repeated postfire flash floods shaped community responses in the burned stream. [ABSTRACT FROM AUTHOR]

Presents the results of an investigation of factors controlling the partitioning of old and new water contributions to stream flow for three events in four catchments (three of which were nested) at Sleepers River Research Watershed in Danville, Vermont. Reconciliation of the contrasting patterns of new-old water partitioning in the three events appears to require an explanation that invokes multiple processes and effects, including: topographically controlled increase in surface-saturated area with increasing catchment size; direct runoff over frozen ground; low infiltration in agriculturally compacted soils; differences in soil transmissivity, which may be more relevant under dry antecedent conditions. These data highlight some of the difficulties faced by catchment hydrologists in formulating a theory of runoff generation at varying basin scales.

Discusses global change and the water cycle in relation to a search for Mauna Loa.