ALBERT

Description: Coastally trapped waves, which are generated by alongshore wind and propagate along a coastline, are common around Australia's southern coast. Some details of the propagation of coastally trapped waves are still uncertain, partly because of the relatively coarse resolution of tide gauge observations as well as the complex ocean bottom surface over which the waves propagate. There has been some debate on the mechanism by which these waves propagate from the southern to eastern coasts of Australia.

Description: Mike Carr wrote recently of the wonderful planetary geology accomplished by NASA over the past 50 years of space exploration, with images and descriptions from the early Venus, Mars, and lunar missions as well as more recent missions, which evoked good memories (M. H. Carr, Geologic exploration of the planets: The first 50 years, Eos , 94 (3), 29–30, doi:10.1029/2013EO030001, 2013). Unfortunately, memories are not science data, and those 50 years have not been as kind to the scientific information collected by these pioneering missions.

Description: Numerical simulations have shown that the moisture in the tropical troposphere has a tendency to spontaneously aggregate, forming separate wet and dry regions. To learn more about how this self-organization occurs, Craig and Mack introduced a simple equation for the tropical troposphere moisture budget and conducted numerical simulations that included convective moistening and horizontal mixing. Based on their simulations, the authors propose that a feedback process in the troposphere causes moisture to aggregate, beginning on small scales and then coarsening to larger scales. Wet regions become wetter and dry regions become drier as the self-organization continues.

Description: Scientists generally believe that the Hawaiian Islands formed primarily through endogenous growth, or intrusion, in which hot magma intrudes into a rock and then solidifies before it reaches the surface. However, a new study suggests that the islands may actually have formed primarily through extrusion, which occurs when a volcano erupts and magma reaches the surface and flows away from the eruption site before cooling and solidifying.

Description: The general circulation model (GCM) experiments conducted under the Coupled Model Intercomparison Project Phase 5 (CMIP5) [ Taylor et al ., 2012], which is being conducted in preparation for the Intergovernmental Panel on Climate Change's Fifth Assessment Report, provide fundamental data sets for assessing the effects of global climate change. However, efforts to assess regional or local effects of the projected changes in climate are often impeded by the coarse spatial resolution of the GCM outputs, as well as potential local or regional biases in GCM outputs [ Fowler et al ., 2007].

Description: Black carbon, also known as soot, emitted from combustion of fuels and biomass burning absorbs solar radiation in the atmosphere and is one of the major causes of global warming, after carbon dioxide emissions. When black carbon is deposited on snow and ice, the soot-covered snow or ice absorbs more sunlight, leading to surface warming. Due to the large amount of snow and ice in the Arctic—which has warmed twice as fast as the global average over the past century—the region is likely to be especially sensitive to black carbon.

Description: In 1999, researchers published data from ice cores collected at Law Dome, a research site in East Antarctica. These data are distinguished by their high time resolution and by their overlap with modern measurements, providing one of the most important records of how the atmosphere's chemical composition changed over the past 1000 years. Air trapped in bubbles in the ice core let researchers measure the concentration of carbon dioxide and other gases and analyze the ratio of carbon-13 to carbon-12 isotopes in the atmospheric carbon dioxide. Burning fossil fuel releases carbon dioxide that is depleted in carbon-13 isotopes, and the Law Dome record provided evidence that modern increases in atmospheric carbon dioxide are due to anthropogenic activity. In a new study, Rubino et al ., a team that includes some of the authors from the original analysis, use novel tools and techniques to update their ice core record.

Description: At present continental to global scale flood forecasting predicts at a point discharge, with little attention to detail and accuracy of local scale inundation predictions. Yet, inundation variables are of interest and all flood impacts are inherently local in nature. This paper proposes a large scale flood inundation ensemble forecasting model that uses best available data and modeling approaches in data scarce areas. The model was built for the Lower Zambezi River to demonstrate current flood inundation forecasting capabilities in large data-scarce regions. ECMWF ensemble forecast (ENS) data were used to force the VIC (Variable Infiltration Capacity) hydrological model, which simulated and routed daily flows to the input boundary locations of a 2-D hydrodynamic model. Efficient hydrodynamic modeling over large areas still requires model grid resolutions that are typically larger than the width of channels that play a key a role in flood wave propagation. We therefore employed a novel sub-grid channel scheme to describe the river network in detail whilst representing the floodplain at an appropriate scale. The modeling system was calibrated using channel water levels from satellite laser altimetry and then applied to predict the February 2007 Mozambique floods. Model evaluation showed that simulated flood edge cells were within a distance of between one and two model resolutions compared to an observed flood edge and inundation area agreement was on average 86%. Our study highlights that physically plausible parameter values and satisfactory performance can be achieved at spatial scales ranging from tens to several hundreds of thousands of km 2 and at model grid resolutions up to several km 2 .

Description: A class of capillary flows in unsaturated porous media is characterized by quasi-steady viscous flow confined behind curved air-water interfaces and within liquid bodies held by capillary forces along crevices and grain contacts. The geometry of the connected capillary liquid network within the pore space resembles channels that form between adjacent bubbles in foam (Plateau borders) with solid grains representing gas bubbles in foam. For simplified channel geometry we combine expressions for viscous flow with continuity considerations to describe the evolution of the channels cross-sectional area during gravity drainage. This formulation enables modeling of unsaturated flow without invoking the Richards equation and associated hydraulic functions. We adapt a formalism originally developed for foam “free drainage” (drainage under gravity) or “forced drainage” (infiltration front motion) to a class of unsaturated flows in porous media that require a few input parameters only (mean channel corner angle, air entry value and porosity) for certain initial and boundary conditions. We demonstrate that the reduction in capillary channel cross section yields a consistent description of self-regulating internal fluxes towards attainment of the so-called “field capacity” in soil and provides an alternative method for interpretation of outflow experiments for prescribed pressure boundary conditions. Additionally, the geometrically-explicit formulation provides a more intuitive picture of capillary flows across textural boundaries (changes in channel cross-section and number of channels). The foam drainage methodology expands the range of tools available for analyses of unsaturated flow processes and offers more realistic links between liquid configuration and flow dynamics in unsaturated porous media.

Description: Synthetic streamflows at different sites in a river basin are needed for planning, operation and management of water resources projects. Modeling the temporal and spatial dependence structure of monthly streamflow at different sites is generally required. In this study, the maximum entropy copula method is proposed for multisite monthly streamflow simulation, in which the temporal and spatial dependence structure is imposed as constraints to derive the maximum entropy copula. The monthly streamflows at different sites are then generated by sampling from the conditional distribution. A case study for the generation of monthly streamflow at three sites in the Colorado River basin illustrates the application of the proposed method. Simulated streamflow from the maximum entropy copula is in satisfactory agreement with observed streamflow.

Description: The Krycklan Catchment Study (KCS) provides a unique field infrastructure for hillslope to landscape-scale research on short and long-term ecosystem dynamics in boreal landscapes. The site is designed for process-based research assessing the role of external drivers including forest management, climate change, and long-range pollutant transport on forests, mires, soils, streams, lakes and groundwater. The over-arching objectives of KCS are to (1) provide a state-of-the-art infrastructure for experimental and hypothesis driven research, (2) maintain a collection of high quality, long-term climatic, biogeochemical, hydrological and environmental data, and (3) support the development of models and guidelines for research, policy and management.

Description: 3-D Hydraulic Tomography (3-D HT) is a method for aquifer characterization whereby the 3-D spatial distribution of aquifer flow parameters (primarily hydraulic conductivity, K) is estimated by joint inversion of head change data from multiple partially-penetrating pumping tests. While performance of 3-D HT has been studied extensively in numerical experiments, few field studies have demonstrated the real-world performance of 3-D HT. Here we report on a 3-D transient hydraulic tomography (3-D THT) field experiment at the Boise Hydrogeophysical Research Site which is different from prior approaches in that it represents a “baseline” analysis of 3-D THT performance using only a single arrangement of a central pumping well and 5 observation wells with nearly complete pumping and observation coverage at 1m intervals. We jointly analyze all pumping tests using a geostatistical approach based on the quasi-linear estimator of kitanidis [1995]. We reanalyze the system after progressively removing pumping and/or observation intervals; significant progressive loss of information about heterogeneity is quantified as reduced variance of the K field overall, reduced correlation with slug test K estimates at wells, and reduced ability to accurately predict independent pumping tests. We verify that imaging accuracy is strongly improved by pumping and observational densities comparable to the aquifer heterogeneity geostatistical correlation lengths. Discrepancies between K profiles at wells, as obtained from HT and slug tests, are greatest at the tops and bottoms of wells where HT observation coverage was lacking.

Description: Probabilistic estimates of future water levels and river discharge are usually simulated with hydrologic models using ensemble weather forecasts as main inputs. As hydrologic models are imperfect and the meteorological ensembles tend to be biased and underdispersed, the ensemble forecasts for river runoff typically are biased and underdispersed, too. Thus, in order to achieve both reliable and sharp predictions statistical post-processing is required. In this work Bayesian model averaging (BMA) is applied to statistically post-process ensemble runoff raw forecasts for a catchment in Switzerland, at lead-times ranging from 1 to 240 hours. The raw forecasts have been obtained using deterministic and ensemble forcing meteorological models with different forecast lead-time ranges. First, BMA is applied based on mixtures of univariate normal distributions, subject to the assumption of independence between distinct lead-times. Then, the independence assumption is relaxed in order to estimate multivariate runoff forecasts over the entire range of lead-times simultaneously, based on a BMA version that uses multivariate normal distributions. Since river runoff is a highly skewed variable, Box-Cox transformations are applied in order to achieve approximate normality. Both univariate and multivariate BMA approaches are able to generate well calibrated probabilistic forecasts that are considerably sharper than climatological forecasts. Additionally, multivariate BMA provides a promising approach for incorporating temporal dependencies into the post-processed forecasts. Its major advantage against univariate BMA is an increase in reliability when the forecast system is changing due to model availability.

Description: In January 2013, approximately 2 months after Hurricane Sandy made landfall in the Mid-Atlantic Bight, scientists from the University of Texas Institute for Geophysics (UTIG), part of the Jackson School of Geosciences (JSG), partnered with local colleagues at Adelphi and Stony Brook universities and the U.S. Geological Survey (USGS) to conduct marine surveys both offshore and within inshore bays of Long Island, N. Y. (Figure 1a). The primary goal was to assess the storm's impact on the seabed.

Description: Volcanic craters are often formed by multiple subsurface explosions caused by the interaction of magma and groundwater [ Lorenz , 1973; Valentine and White , 2012]. To understand the processes and products of such explosions, scientists spent 2 years conducting experiments that produced craters on the meter scale at the Geohazards Field Station in Ashford, N. Y.

Description: A sudden shift in the strength of the Atlantic meridional overturning circulation (AMOC) is thought to be the most important mechanism behind several past abrupt changes in the climate. AMOC transports heat, salt, and nutrients throughout the Atlantic Ocean. Paleoclimate evidence has shown that changes in its strength affect the climate worldwide. Whether AMOC could suddenly shift again depends on whether the circulation can exist in more than one stable state.

Description: One of the most important services performed for AGU is the conscientious reviewing of submitted papers. Because of the nature of the reviewing process, this service is also one of the least recognized. Every year editors are asked to select the outstanding reviewers from the previous year. The reviewers listed below have been cited by editors of AGU journals and Eos for excellence in refereeing. These individuals are to be commended for consistently providing constructive and thoughtful reviews .

Description: In the 1930s, researchers first noticed that the Chesapeake Bay had a dead zone, an expanse of water with drastically reduced concentrations of oxygen. In the 1980s, hypoxia—low-oxygen conditions—gave way in some places to anoxia—a near-total depletion of dissolved oxygen. A lack of oxygen makes the water inhospitable for many marine organisms, and the Chesapeake Bay is the focus of major ecosystem rehabilitation efforts.

Description: We derive a series solution for the nonlinear Boussinesq equation in terms of the similarity variable of the Boltzmann transformation in a semi-infinite domain. The first few coefficients of the series have been known for a long time, having been obtained by a truncated inversion of the series solution of the Blasius equation, but no direct recurrence relation was known for the complete series representing the solution of the Boussinesq equation. The series turns out to have a finite radius of convergence, which we estimate with a numerical complex-plane integration method that identifies the singularities of the solution when the equation is extended to the complex plane. The homogeneous condition at the origin produces a singularity which complicates numerical solutions with Runge-Kutta methods. We present two variable transformations that circumvent the problem and that are best suited to the complex-variable and the real-variable versions of the equation, respectively. Using those tools, an approximate solution accurate to 1.75 × 10 -10 and valid for the entire positive real axis is then developed by matching a Padé approximant of the exact series and an asymptotic solution (to overcome the restriction imposed by the finite radius of convergence of the series), along the same lines of the expression proposed by Hogarth and Parlange [1999]. The accuracies of all of the existing and the newly proposed solutions are obtained.

Description: Field sampling in unwadeable and flashy flood events encounters the problem that lateral variability of flow hydraulics and sediment transport cannot be captured adequately, and there is also an accuracy problem because parameters change while being measured. Moreover, event based gravel-sand mixed transport data in rapidly changing conditions are largely missing, in particular for gravel-bed rivers in small catchments. In this study, field measurements of bed load, suspended load, flow velocities, water depths and cross section geometry were collected during flood events at a monitoring station near the mouth of the Versilia river, Italy. Since the observed hydrographs are characterized by short durations, to the order of a few hours, an analysis of the lateral and temporal flow variability was carried out to enable the design of a sampling strategy and to minimize the errors created by the time variations of discharge associated with unsteady flow conditions. The measurements were interpreted using a 1D hydro-morphodynamic numerical model simulating the dynamics of flow and sediment discharges during a flood event for a given return period. The flow and sediment rating curves were then developed through an integrated approach combining different methodologies: field measurements, laboratory analyses and mathematical modeling. The developed approach allows one to capture the main physical mechanisms associated to the transport of sand–gravel mixtures, such as selective transport, and the hysteretic behaviour of sediment transport produced by rapid and intense flood events.

Description: Patterns of past, present, and future sea level vary spatially, depending on how the solid Earth responds to the changing distribution of ice and ocean mass, known as glacial isostatic adjustment (GIA). Accurate interpretation of observational constraints on GIA requires dialogue between field scientists and researchers who reconstruct ice sheet geometries, infer Earth structure and rheology, and model the solid Earth response to loading.

Description: Fieldwork plays an important role in initiating students into the geoscience community of practice, providing learning opportunities not possible through classroom lectures, lab work, or computer exercises alone [ Mogk and Goodwin , 2012]. It's no wonder, then, that fieldwork is a mainstay of any well-balanced university geoscience program, with activities ranging from local field trips to in-residence field camps at remote sites.

Description: AGU members are invited to comment on proposed changes to AGU's bylaws. The updates reflect changes required by Washington, D. C., law and changes enacted by the AGU Board of Directors and Council during the transition in 2010–2012 to a new governance structure. Members can view and comment on the proposed changes at http://sites.agu.org/leadership/agu-bylaws-comment-period/ . The comment period is open until 18 November.

Description: It is a great pleasure for me to introduce Giuliano Di Baldassarre as the recipient of the AGU Hydrologic Sciences Early Career Award.

Description: Agricultural ecologist David Lobell is among the 2103 class of MacArthur Fellows, the MacArthur Foundation announced on 25 September. Lobell, an associate professor in Stanford University's Department of Environmental Earth System Science, is one of 24 people to win the “genius award” this year. The citation for Lobell notes that he “unearths and connects richly informative sources of data to investigate the impact of climate change on crop production and food security around the globe. His multidisciplinary background in remote sensing, statistics, ecosystem modeling, land use, and agronomy informs his approach and enables him to draw significant insights from enormous and diverse data sets on weather, agricultural practices, and natural resources such as soil and water.” Each MacArthur Fellow receives a no-strings-attached stipend of $625,000 over 5 years.

Description: Estimates of the recent decline in Arctic Ocean summer sea ice extent can vary due to differences in sea ice data sources, in the number of years used to compute the trend, and in the start and end years used in the trend computation. Compounding such differences, estimates of the relative decline in sea ice cover (given in percent change per decade) can further vary due to the choice of reference value (the initial point of the trend line, a climatological baseline, etc.). Further adding to the confusion, very often when relative trends are reported in research papers, the reference values used are not specified or made clear. This can lead to confusion when trend studies are cited in the press and public reports.

Description: The stability of the Amazon rainforest and the ecosystem's resilience to widespread deforestation may be much lower than previously thought. The replacement of stands of trees with grassland changes evapotranspiration rates and atmospheric moisture convergence, which, in turn, reduce regional rainfall. This feedback effect could drive further deforestation. Previous research indicated that a dramatic shift from forest to grassland could overtake the Amazon when the total deforested area hits 40% to 50% of the forest's current size. New research by Pires and Costa , however, found that the deforestation needed to trigger this equilibrium shift is much lower, closer to just 10%.

Description: In the western South Atlantic, off the coast of South America, a band of cold, fresh, nutrient-rich Sub-Antarctic Shelf Water (SASW) meets warm, salty, nutrient-poor Subtropical Shelf Water (STSW) to form the Subtropical Shelf Front (STSF). This front is the shallow-water expression of the major Brazil-Malvinas Confluence Zone and has moved northward and southward during the Holocene (the past ~12,000 years). Bender et al . reconstruct the latitudinal shifts of the STSF over the past 11,000 calendar-equivalent years using records of oxygen and carbon stable isotope compositions of benthic foraminifera and total organic carbon and calcium carbonate content from a sediment record collected off Uruguay. These measurements serve as proxies for ocean water temperature and nutrient content, which can be used to distinguish the SASW and STSW.

Description: The stability of the West Antarctic Ice Sheet is uncertain as climate changes. An ice sheet such as the West Antarctic Ice Sheet that is grounded well below sea level on a bed that slopes toward the interior of the sheet is believed to be unstable: When the grounding zone, where the grounded sheet transitions into floating ice, retreats inland, it can lead to massive amounts of ice becoming ungrounded and floating into the ocean unless something such as a wedge of sediment stabilizes the ice sheet. It has been proposed that such a sediment wedge stabilizes the grounding zone of the Whillans Ice Stream, one of the large ice streams flowing from the West Antarctic Ice Sheet. However, most understanding of ice sheet stability at grounding zones comes from models and remote observation rather than field-based observations.

Description: Particulate matter in the air, which can come from both natural and anthropogenic sources, can be detrimental to human health. Air quality standards in Europe and elsewhere regulate emission of air pollutants from human sources, but in some locations, particulate matter levels are still high. Among the natural factors that can influence particulate matter concentrations are large-scale atmospheric circulation patterns, such as the North Atlantic Oscillation (NAO). Understanding the relationship between NAO variability and particulate matter can help scientists understand particulate matter trends and potentially predict areas likely to be affected by pollution episodes. This is especially important because climate models suggest that the winter mean state of the NAO is likely to shift in coming years.

Description: ABSTRACT A study was performed to characterize over land precipitation associated with tropical cyclones (TCs) for basins around the world based upon the International Best Track Archive for Climate Stewardship (IBTrACS). From 1998 to 2009, data from the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) product 3B42, showed that TCs accounted for 5.5%, 7.5%, 6%, 9.5%, and 8.9% of the annual precipitation for impacted over land areas of the Americas, East Asia, South and West Asia, Oceania, and East Africa respectively, and that TC contribution decreased significantly within the first 150-km from the coast. Locally, TCs contributed on average to more than 25% and up to 61% of the annual precipitation budget over very different climatic areas with arid or tropical characteristics. East Asia represented the higher and most constant TC rain (118±19% mm y -1 ) normalized over the area impacted, while East Africa presented the highest variability (108±60% mm y -1 ), and the Americas displayed the lowest average TC rain (65±24% mm y -1 ) despite a higher TC activity. Furthermore, the maximum monthly TC contribution (8-11%) was found later in the TC season and depended on the peak of TC activity, TC rainfall, and the domain transition between dry and wet regimes if any. Finally, because of their importance in terms of rainfall amount, the contribution of TCs was provided for a selection of 50 urban areas experiencing cyclonic activity. Results showed that for particularly intense years, urban areas prone to cyclonic activity received more than half of their annual rainfall from TCs.

Description: A multivariate, multi-site daily weather generator is presented for use in decision-centric vulnerability assessments under climate change. The tool is envisioned useful for a wide range of socioeconomic and biophysical systems sensitive to different aspects of climate variability and change. The proposed stochastic model has several components, including 1) a wavelet decomposition coupled to an autoregressive model to account for structured, low-frequency climate oscillations, 2) a Markov Chain and k-nearest-neighbor (KNN) resampling scheme to simulate spatially-distributed, multivariate weather variables over a region, and 3) a quantile mapping procedure to enforce long-term distributional shifts in weather variables that result from prescribed climate changes. The Markov Chain is used to better represent wet and dry spell statistics while the KNN bootstrap resampler preserves the covariance structure between the weather variables and across space. The wavelet-based autoregressive model is applied to annual climate over the region and used to modulate the Markov Chain and KNN resampling, embedding appropriate low-frequency structure within the daily weather generation process. Parameters can be altered in any of the components of the proposed model to enable the generation of realistic time series of climate variables that exhibit changes to both lower-order and higher-order statistics at long-term (inter-annual), mid-term (seasonal), and short-term (daily) timescales. The tool can be coupled with impact models in a bottom-up risk assessment to efficiently and exhaustively explore the potential climate changes under which a system is most vulnerable. An application of the weather generator is presented for the Connecticut River basin to demonstrate the tool's ability to generate a wide range of possible climate sequences over an extensive spatial domain.

Description: The objective of the least cost design problem of a water distribution system is to find its minimum cost with discrete diameters as decision variables and hydraulic controls as constraints. The goal of a robust least cost design is to find solutions which guarantee its feasibility independent of the data (i.e., under model uncertainty). A robust counterpart approach for linear uncertain problems is adopted in this study, which represents the uncertain stochastic problem as its deterministic equivalent. Robustness is controlled by a single parameter providing a trade-off between the probability of constraint violation and the objective cost. Two principal models are developed-uncorrelated uncertainty model with implicit design reliability, and correlated uncertainty model with explicit design reliability. The models are tested on three example applications and compared for uncertainty in consumers’ demands. The main contribution of this study is the inclusion of the ability to explicitly account for different correlations between water distribution systems demand nodes. In particular it is shown that including correlation information in the design phase has a substantial advantage in seeking more efficient robust solutions.

Description: Moving from univariate to multivariate frequency analysis, this study extends the Klemeš' critique of the widespread belief that the increasingly refined mathematical structures of probability functions increase the accuracy and credibility of the extrapolated upper tails of the fitted distribution models. In particular, we discuss key aspects of multivariate frequency analysis applied to hydrological data such as the selection of multivariate design events (i.e., appropriate subsets or scenarios of multiplets that exhibit the same joint probability to be used in design applications) and the assessment of the corresponding uncertainty. Since these problems are often overlooked or treated separately, and sometimes confused, we attempt to clarify properties, advantages, shortcomings and reliability of results of frequency analysis. We suggest a selection method of multivariate design events with prescribed joint probability based on simple Monte Carlo simulations that accounts for the uncertainty affecting the inference results and the multivariate extreme quantiles. It is also shown that the exploration of the p -level probability regions of a joint distribution returns a set of events that is a subset of the p -level scenarios resulting from an appropriate assessment of the sampling uncertainty, thus tending to overlook more extreme and potentially dangerous events with the same (uncertain) joint probability. Moreover, a quantitative assessment of the uncertainty of multivariate quantiles is provided by introducing the concept of joint confidence intervals. From an operational point of view, the simulated event sets describing the distribution of the multivariate p -level quantiles can be used to perform multivariate risk analysis under sampling uncertainty. As an example of the practical implications of this study, we analyse two case studies already presented in the literature.

Description: Sparse geologic dictionaries provide a novel approach for subsurface flow model representation and calibration. Learning sparse dictionaries from prior training datasets is an effective approach to describe complex geologic connectivity patterns in subsurface imaging applications. However, the computational cost of sparse learning algorithms becomes prohibitive for large models. Performing the sparse dictionary learning process on smaller image patches (segments) provides a simple approach to address this problem in image processing applications. However, in underdetermined subsurface flow model calibration inverse problems, reconstruction of a segmented image can introduce significant structural distortion and discontinuity at the boundaries of the segments. This paper proposes an alternative sparse learning approach where the sparse dictionaries are learned from low-rank representations of the large-scale training dataset in spectral domains (e.g., frequency domain). The objective is to develop a computationally efficient dictionary learning approach that emphasizes large-scale spatial connectivity patterns. This is achieved by removing the strong spatial correlations in the training data, thereby eliminating a large number of insignificant components from the sparse learning computation. In addition to improving the computational complexity, sparse learning from low-rank training datasets suppresses the small-scale details from entering the reconstruction of large-scale connectivity patterns, and providing a regularization effect in solving the resulting ill-posed inverse problems. We apply the proposed approach to travel-time tomography inversion and nonlinear subsurface flow model calibration inverse problems to demonstrate its effectiveness and practicality.

Description: Due to its massive air traffic impact, the 2010 eruption of Eyjafjallajökull was felt by millions of people and cost airlines more than U.S. $1.7 billion. The event has, thus, become widely cited in renewed efforts to improve real-time tracking of volcanic plumes, as witnessed by special sections published last year in Journal of Geophysical Research , ( 117 , issues D20 and B9).

Description: The National Oceanic and Atmospheric Administration (NOAA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) have agreed to continue their long-term cooperation on satellite-based weather monitoring. NOAA acting administrator Kathryn Sullivan and EUMETSAT director general Alain Ratier signed the agreement at a ceremony at the European Union Delegation in Washington, D. C., on 27 August.

Description: From May to July 2012, the Great Plains region of the western United States faced a powerful and unpredicted drought. Following 7 months of normal rainfall, the drought was one of the largest deviations from seasonal precipitation rates seen in the region since observations began in 1895. When such extreme events take place today against the backdrop of ongoing global climate change, they raise questions about the relationship between climate change and natural disasters.

Description: A binational research team met on the campus of Yunnan University in Kunming, China, to discuss recent progress and future plans to leverage binational support to address major questions on life in terrestrial geothermal systems. The symposium included about 90 faculty, postdocs, and students from China and about 30 faculty, postdocs, students, and high school teachers from the United States. The introductory session reviewed the progress of the Tengchong PIRE project funded by the U.S. National Science Foundation (NSF) Partnerships for International Research and Education (PIRE) program (OISE-0836450). It also introduced a new collaborative project funded as a Key Project of International Cooperation by the Chinese Ministry of Science and Technology (MOST, 2013DFA31980), which is the first project funded through a memorandum of understanding between NSF and MOST to promote China-U.S. collaboration.

Description: A new hybrid wavelet–bootstrap–neural network (WBNN) model is proposed in this study for short term (1, 3 and 5 day; 1 and 2 week; and 1 and 2 month) urban water demand forecasting. The new method was tested using data from the city of Montreal in Canada. The performance of the WBNN method was compared with the autoregressive integrated moving average (ARIMA) and autoregressive integrated moving average model with exogenous input variables (ARIMAX), traditional NNs, wavelet analysis based NNs (WNN), bootstrap based NNs (BNN), and a simple naïve persistence index model. The WBNN model was developed as an ensemble of several NNs built using bootstrap resamples of wavelet sub-time series instead of raw datasets. The results demonstrated that the hybrid WBNN and WNN models produced significantly more accurate forecasting results than the traditional NN, BNN, ARIMA and ARIMAX models. It was also found that the WBNN model reduces the uncertainty associated with the forecasts, and the performance of WBNN forecasted confidence bands were found to be more accurate and reliable than BNN forecasted confidence bands. It was found in this study that maximum temperature and total precipitation improved the accuracy of water demand forecasts using wavelet analysis. The performance of WBNN models was also compared for different numbers of bootstrap resamples (i.e., 25, 50, 100, 200, and 500) and it was found that WBNN models produced optimum results with different numbers of bootstrap resamples for different lead time forecasts with considerable variability.

Description: Recent observations show that the Sun's magnetic field is flipping, marking one of the weakest sunspot cycle maxima in recent history. Many consequences have been observed and are under study, from a significant diminishing of the upper atmosphere's density [ Solomon et al ., 2010] to record low levels of geomagnetic activity [ Richardson , 2013] to the large increase of local galactic cosmic ray fluxes starting in the preceding solar minimum [ Mewaldt et al ., 2010].

Description: I'm deeply honored to receive the Earth and Planetary Surface Processes G. K. Gilbert Award, in no small part because Gilbert's application of simple physical principles to Earth surface processes has always been an inspiration to me. My desire to study the transportation of debris by running water started a long time ago on our family farm, where re-engineering the local stream with a backhoe was a rewarding afternoon activity.

Description: Michael Lamb received the 2012 Luna B. Leopold Young Scientist Award at the 2012 AGU Fall Meeting, held 3–7 December in San Francisco, Calif. The award recognizes “a young scientist for making a significant and outstanding contribution that advances the field of Earth and planetary surface processes.”

Description: It is my pleasure to be a part of the exciting community of Earth and planetary surface processes. In addition to the opportunities to participate in engaging and fundamental science, I enjoy our field because of collaborations with bright and fun people. In my short career I have had the pleasure to work with a number of colleagues, and I share this award with you.

Description: Climate models generally show that when a massive volcano erupts, scattering reflective aerosols across the globe, the planet's temperature declines for up to a few years. However, when researchers look at reconstructed temperature records built on annual tree ring measurements, this volcanic cooling often appeared much weaker than expected or was nonexistent. In a new study reanalyzing regional tree ring growth records, Mann et al . provide a possible explanation for the absence of the cooling effect.

Description: Tree ring records are often used as a proxy for past climate. Trees form a new growth ring each year, and ring widths are related to temperature and other conditions at cold sites. Some recent studies have noted that tree ring width chronologies and resulting climate reconstructions do not appear to show the widespread cooling in the past millennium that would be expected following large volcanic eruptions. One hypothesis suggests that regional cooling after a volcanic eruption could be so severe that many trees do not form a ring at all, which leads researchers to misdate the tree ring chronology.

Description: In the Luzon Strait, which lies between the Philippines and Taiwan and connects the western Pacific Ocean and the South China Sea, ridges extending along the ocean bottom generate large internal tides—waves with a tidal frequency within the ocean, not on its surface—that propagate into the South China Sea and the Pacific Ocean.

Description: ABSTRACT Although mechanistic reaction networks have been developed to quantify the biogeochemical evolution of subsurface systems associated with bioremediation, it is difficult in practice to quantify the onset and distribution of these transitions at the field scale using commonly collected wellbore datasets. As an alternative approach to the mechanistic methods, we develop a data-driven, statistical model to identify biogeochemical transitions using various time-lapse aqueous geochemical data (e.g., Fe(II), sulfate, sulfide, acetate, and uranium concentrations) and induced polarization (IP) data. We assume that the biogeochemical transitions can be classified as several dominant states that correspond to redox transitions and test the method at a uranium-contaminated site. The relationships between the geophysical observations and geochemical time-series vary depending upon the unknown underlying redox status, which is modeled as a hidden Markov random field. We estimate unknown parameters by maximizing the joint likelihood function using the maximization-expectation algorithm. The case study results show that when considered together aqueous geochemical data and IP imaginary conductivity provide a key diagnostic signature of biogeochemical stages. The developed method provides useful information for evaluating the effectiveness of bioremediation, such as the probability of being in specific redox stages following biostimulation where desirable pathways (e.g., uranium removal) are more highly favored. The use of geophysical data in the approach advances the possibility of using non-invasive methods to monitor critical biogeochemical system stages and transitions remotely and over field relevant scales (e.g., from square meters to several hectares).

Description: In recent years, a number of numerical modelling studies of transient sea-level rise (SLR) and seawater intrusion (SWI) in flux-controlled systems have reported an overshoot phenomenon, whereby the freshwater-saltwater interface temporarily extends further inland than the eventual steady-state position. In this study, we have carried out physical sand tank modelling of SLR-SWI in a flux-controlled unconfined aquifer setting to test if SWI overshoot is a measurable physical process. Photographs of the physical SLR experiments show, for the first time, that an overshoot occurs under controlled laboratory conditions. A sea-level drop (SLD) experiment was also carried out, and overshoot was again observed, whereby the interface was temporarily closer to the coast than the eventual steady-state position. This shows that an overshoot can occur for the case of a retreating interface. Numerical modelling corroborated the physical SLR and SLD experiments. The magnitude of the overshoot for SLR and SLD in the physical experiments was 24% of the change in steady-state interface position, albeit the laboratory setting is designed to maximise overshoot extent by adopting high groundwater flow gradients and large and rapid sea-level changes. While the likelihood of overshoot at the field scale appears to be low, this work has shown that it can be observed under controlled laboratory conditions.

Description: A new analytical solution of the flow equation has been developed to estimate the time to reach a near-equilibrium state in mixed aquifers, i.e. having unconfined and confined portions, following a large hydraulic perturbation. Near-equilibrium is defined as the time for an initial aquifer perturbation to dissipate by an average 95% across the aquifer.The new solution has been obtained by solving the flow system of a simplified conceptual model of a mixed aquifer using Laplace transforms. The conceptual model is based on two assumptions: 1) the groundwater flow can be reduced to a horizontal 1D problem; and 2) the transmissivity, a function of the saturated thickness, is assumed constant on the unconfined portion. This new solution depends on the storativity of the unconfined portion, the lengths of the unconfined and confined portions and the transmissivity, assumed to be constant and equal in both portions of the mixed aquifer. This solution was then tested and validated against a numerical flow model, where the variations of the saturated thickness and therefore variations of the transmissivity were either ignored, or properly modeled. The agreement between the results from the new solution and those from the numerical model is good, validating the use of this new solution to estimate the time to reach near-equilibrium in mixed aquifers. This solution for mixed aquifers, as well as the solutions for a fully confined or fully unconfined aquifer, have been used to estimate the time to reach near-equilibrium in thirteen large aquifers in the world. For those different aquifers, the time to reach near-equilibrium ranges between 0.7 ky to 2.4x10 7 ky. These results suggest that the present hydraulic heads in these aquifers are typically a mixture of responses induced from current and past hydrologic conditions and thus climate conditions. For some aquifers, the modern hydraulic heads may in fact depend upon hydrologic conditions resulting from several past climate cycles.

Description: The impact of contact angle on 2D spatial and temporal water content distribution during infiltration and drainage was experimentally studied. The 0.3-0.5 mm fraction of a quartz dune sand was treated and turned sub-critically repellent (contact angle of 33 0 , 48 0 , 56 0 , and 75 0 for S33, S48, S56, and S75, respectively). The media were packed uniformly in transparent flow chambers and water was supplied to the surface as a point source at different rates (1 to 20 ml/min). A sequence of grey-value images was taken by CCD camera during infiltration and subsequent drainage; grey values were converted to volumetric water content by water volume balance. Narrow and long plumes with water accumulation behind the downward moving wetting front (tip) and negative water gradient above it (tail) developed in the S56 and S75 media during infiltration at lower water application rates. The plumes became bulbous with spatially uniform water content distribution as water application rates increased. All plumes in these media propagated downward at a constant rate during infiltration and were frozen during drainage. In contrast, regular plume shapes were observed in the S33 and S48 media at all flow rates, and drainage profiles were non-monotonic with a transition plane at the depth that water reached during infiltration. Given that the studied media have similar pore-size distributions, the conclusion is that imbibition hindered by the non-zero contact angle induced pressure buildup at the wetting front (dynamic water entry value) that controlled the plume shape and internal water-content distribution during infiltration and drainage.

Description: Estimation of design quantiles of hydro-meteorological variables at critical locations in river basins is necessary for hydrological applications. To arrive at reliable estimates for locations (sites) where no or limited records are available, various regional frequency analysis (RFA) procedures have been developed over the past five decades. The most widely used procedure is based on Index-flood approach and L -moments. It assumes that values of scale and shape parameters of frequency distribution are identical across all the sites in a homogeneous region. In real world scenario, this assumption may not be valid even if a region is statistically homogeneous. To address this issue, a novel mathematical approach is proposed. It involves (i) identification of an appropriate frequency distribution to fit the random variable being analyzed for homogeneous region, (ii) use of a proposed transformation mechanism to map observations of the variable from original space to a dimensionless space where the form of distribution does not change, and variation in values of its parameters is minimal across sites, (iii) construction of a growth curve in the dimensionless space, and (iv) mapping the curve to the original space for the target site by applying inverse transformation to arrive at required quantile(s) for the site. Effectiveness of the proposed approach in predicting quantiles for ungauged sites is demonstrated through Monte-Carlo simulation experiments considering five frequency distributions that are widely used in RFA, and by case study on watersheds in conterminous United States. Results indicate that the proposed approach outperforms methods based on index-flood approach.

Description: Prediction of microbial surface water contamination is a formidable task because of the inherent randomness of environmental processes driving microbial fate and transport. In this article we develop a theoretical framework of a fully stochastic model of microbial transport in watersheds, and apply the theory to a simple flow network to demonstrate its use. The framework bridges the gap between microscopic behavior of individual microorganisms and macroscopic ensemble dynamics. This scaling is accomplished within a single mathematical framework, where each microorganism behaves according to a continuous-time discrete-space Markov process, and the Markov behavior of individual microbes gives rise to a non-homogeneous Poisson random field that describes microbial population dynamics. Mean value functions are derived, and the spatial and temporal distribution of water contamination risk is computed in a straightforward manner.

Description: For the past few decades the upper reaches of Earth's atmosphere have been cooling much faster than researchers anticipated. While the rising atmospheric concentration of carbon dioxide is heating the air near the ground, that same increase is expected to cool the thermosphere—the atmospheric band that stretches from around 80 kilometers altitude to the exosphere at 500 kilometers—by emitting heat into space. However, while carbon dioxide should theoretically cool the thermosphere by around 2 kelvins per decade, the observed cooling was around 10 times this rate. Building on recent theoretical and modeling work, Oliver et al . lay out a mechanism that could explain the observed cooling.

Description: “We made it,” Voyager project scientist Ed Stone announced at a 12 September briefing at NASA headquarters in Washington, D. C. NASA's Voyager 1 spacecraft, the most distant human-made object, is now the first such object to enter interstellar space, the space between the stars. “The 36-year-old probe is now sailing the uncharted waters of a new cosmic sea, and it has brought us along for the journey,” Stone said.

Description: In the 23 July 2013 issue of Eos , we provided a broad update on recent events in AGU publishing, focusing on the partnership with John Wiley & Sons ( Eos , 94 (30), 264–266, doi:10.1002/2013EO300009). Here we briefly comment on the latest developments in the partnership, but the main focus is on recent events regarding open access as it relates to AGU publishing.

Description: Given today's enormous management and protection challenges related to the world's oceans, a new competition calls on ocean scientists to effectively communicate their research in videos that last up to 3 minutes. The Ocean 180 Video Challenge, named for the number of seconds in 3 minutes, aims to improve ocean science communication while providing high school and middle school teachers and students with new and interesting educational materials about current science topics.

Description: Earth's nighttime environment is being revealed in unprecedented detail by the new satellite-mounted Visible/Infrared Imaging Radiometer Suite (VIIRS). VIIRS' Day/Night Band (DNB) is a highly sensitive broadband visible channel capable of detecting light from cities and other terrestrial emission sources.

Description: Thank you very much, Alberto, for your nice comments and the precious support you have given me since the very beginning of my scientific career.

Description: AGU has created a new award that honors members whose achievements extend beyond those recognized by traditional scientific discipline awards. The award furthers AGU's strategic goals to promote collaboration and innovation, inform society about Earth and space science, and build the global talent pool.

Description: I am delighted to present Professor Gabriel Katul of Duke University with the 2012 Hydrologic Sciences Award. He has made massive contributions to the understanding and prediction of hydrology, and it is for his work that we (Professors Poporato, Hornberger, Rinaldo, Rodriguez-Iturbe, Brutsaert, and Raupach) nominated him.

Description: Space weather can affect satellite performance and cause “anomalies,” unexplained problems ranging from a minor temporary glitch to a complete failure of a component. Understanding these effects requires looking at the relationship between space weather conditions and anomalies. However, data on commercial satellite anomalies have not often been made available for scientists to study.

Description: Dust, which affects weather and climate and can be hazardous to health, can be generated when sand or silt grains are either dislodged from the surface by other windblown grains (saltation) or lifted by wind directly (direct entrainment). Direct entrainment of silt has been thought to generate only minimal quantities of dust, and atmospheric models that include dust usually assume that dust generation occurs through saltation.

Description: Thank you, Marc, for the kind comments and unwavering support as a mentor and friend. I am honored by this award, which I share with many people.

Description: When scientists confirmed on 12 September that NASA's Voyager 1 spacecraft had entered interstellar space ( Eos, 94 (39), 339, doi:10.1002/2013EO390003), the probe was acknowledged as the first human-made object to travel into that realm. The probe and its twin, Voyager 2, each carry a 12-inch gold-plated copper disk, known as the Golden Record.

Description: Humans are now the dominant driver of global climate change. From ocean acidification to sea level rise, changes in precipitation patterns, and rising temperatures, global warming is presenting us with an uncertain future. However, this is not the first time human civilizations have faced a changing world. In the AGU monograph Climates, Landscapes, and Civilizations, editors Liviu Giosan, Dorian Q. Fuller, Kathleen Nicoll, Rowan K. Flad, and Peter C. Clift explore how some ancient peoples weathered the shifting storms while some faded away. In this interview , Eos speaks with Liviu Giosan about the decay of civilizations, ancient adaptation, and the surprisingly long history of humanity's effect on the Earth .

Description: The anomalously snowy winter season of 2010/11 in the Sierra Nevada is analyzed in terms of snow water equivalent (SWE) anomalies and the role of atmospheric rivers (ARs)―narrow channels of enhanced meridional water vapor transport between the tropics and extratropics. Mean April 1 SWE was 0.44 m (56%) above normal averaged over 100 snow sensors. AR occurrence was anomalously high during the period, with 20 AR dates during the season and 14 in the month of December 2010, compared to the mean occurrence of 9 dates per season. Fifteen out of the 20 AR dates were associated with the negative phases of the Arctic Oscillation (AO) and the Pacific-North American (PNA) teleconnection pattern. Analysis of all winter ARs in California during water years 1998–2011 indicates more ARs occur during the negative phase of AO and PNA, with the increase between positive and negative phases being ˜90% for AO, and ˜50% for PNA. The circulation pattern associated with concurrent negative phases of AO and PNA, characterized by cyclonic anomalies centered northwest of California, provides a favorable dynamical condition for ARs. The analysis suggests that the massive Sierra Nevada snowpack during the 2010/11 winter season is primarily related to anomalously high frequency of ARs favored by the joint phasing of −AO and −PNA, and that a secondary contribution is from increased snow accumulation during these ARs favored by colder air temperatures associated with −AO, −PNA and La Niña.

Description: The baseflow recession constant, K b , is used to characterize the interaction of groundwater and surface water systems. Estimation of K b is critical in many studies including rainfall-runoff modeling, estimation of low flow statistics at ungaged locations and baseflow separation methods. The performance of several estimators of K b are compared, including several new approaches which account for the impact of human withdrawals. A traditional semi-log estimation approach adapted to incorporate the influence of human withdrawals was preferred over other derivative-based estimators. Human withdrawals are shown to have a significant impact on the estimation of baseflow recessions, even when withdrawals are relatively small. Regional regression models are developed to relate seasonal estimates of K b to physical, climatic, and anthropogenic characteristics of stream-aquifer systems. Among the factors considered for explaining the behavior of K b , both drainage density and human withdrawals have significant and similar explanatory power. We document the importance of incorporating human withdrawals into models of the baseflow recession response of a watershed and the systemic downward bias associated with estimates of K b obtained without consideration of human withdrawals.

Description: There are significant uncertainties inherent in precipitation forecasts and these uncertainties can be communicated to users via large ensembles that are generated using stochastic models of forecast error. The Met Office and the Australian Bureau of Meteorology developed the Short Term Ensemble Prediction System (STEPS) which has been operational for a number of years. The initial formulation of Bowler et al. [2006] has been revised and extended to improve the performance over large domains, to include radar observation errors, and to facilitate the combination of forecasts from a number of sources. This paper reviews the formulation of STEPS, discusses those aspects of the formulation that have proved most problematic and presents some solutions. The performance of STEPS nowcasts is evaluated using a combination of case study examples and statistical verification from the UK. Routine forecast verification demonstrates that STEPS is capable of producing near optimal blends of a rainfall nowcast and high resolution NWP forecast. It also shows that the spread of STEPS nowcast ensembles are a good predictor of the error in the control member (unperturbed) nowcast.

Description: In this study seasonal and interannual variability of the main atmospheric moisture sources over eight regions in the Mediterranean basin were investigated along a twenty one year period. The Lagrangian dispersion model FLEXPART, developed by Stohl and James [2004, 2005], was applied to identify the contribution of humidity to the moisture budget of each region. This methodology is used to compute budgets of evaporation minus precipitation (E-P) by calculating changes in the specific humidity along backward trajectories, for the preceding ten-day periods. The results show clear seasonal differences in the moisture sources between wet and dry seasons. The Western Mediterranean Sea is the dominant moisture source for almost all the regions in the Mediterranean basin during the wet season, while the local net evaporation dominates during the dry season. The highest interannual variability is found in contributions to the Iberian Peninsula, Italy and the Eastern Mediterranean. It is seen that the role of teleconnections is more limited than for the precipitation recorded in the region.

Description: We present a new hydrologic model based on the frequency distribution of hillslope landscape elements along the stream network as a basis for simulating landscape-scale hydrologic connectivity and catchment runoff. Hydrologic connectivity describes shallow water table continuity between upland and stream elements of the catchment and is important for the movement of water and solutes to streams. This concept has gained traction in physical hydrology but has received less attention in rainfall-runoff modeling. Our model is based on the empirical studies of Jencso et al. [2009; 2010], who found a strong correlation between the duration of shallow groundwater connectivity across hillslope, riparian, and stream zones and upslope accumulated area. We explored the relationship between catchment form and function by testing the extent to which streamflow generation could be predicted by a model based on the topographic form (distribution of landscape elements) of the catchment. We applied the model to the Stringer Creek catchment of the Tenderfoot Creek Experimental Forest, located in Montana, USA. Detailed field observations collected by Jencso et al. [2009] were used to inform the underpinnings of the model and to corroborate internal consistency of the model simulations. The model demonstrated good agreement between the observed and predicted streamflow and connectivity duration curves. The ability of this model to simulate internal dynamics without conditioning the parameters on these data suggests that it has the potential to be more confidently extrapolated to other shallow, topographically driven catchments than hydrologic models that fail to consistently reproduce internal variables.

Description: Knowledge of hydrological model complexity can aid selection of an optimal prediction model out of a set of available models. Optimal model selection is formalized as selection of the least complex model out of a subset of models that have lower empirical risk. This may be considered equivalent to minimizing an upper bound on prediction error, defined here as the mathematical expectation of empirical risk. In this paper we derive an upper bound that is free from assumptions on data and underlying process distribution as well as on independence of model predictions over time. We demonstrate that hydrological model complexity, as defined in the presented theoretical framework, plays an important role in determining the upper bound. The model complexity also acts as a stabilizer to a hydrological model selection problem if it is deemed ill-posed. We provide an algorithm for computing complexity of any arbitrary hydrological model. We also demonstrate that hydrological model complexity has a geometric interpretation as the size of model output space. The presented theory is applied to quantify complexities of two hydrological model structures: SAC-SMA and SIXPAR. It detects that SAC-SMA is indeed more complex than SIXPAR. We also develop an algorithm to estimate the upper bound on prediction error, which is applied on 5 different rainfall-runoff model structures that vary in complexity. We show that a model selection problem is stabilized by regularizing it with model complexity. Complexity regularized model selection yields models that are robust in predicting future but yet unseen data.

Description: The temporal dynamics and spatial distribution of the concentrations of dissolved gases (He, Ar, Kr, N 2 , O 2 and CO 2 ) in an infiltrating groundwater system fed by the peri-alpine River Thur (Switzerland) were analysed before, during and after a single, well-defined flood event. The analysis was based on measurements taken in five different groundwater observation wells that were located approximately 10 m apart and tapped the same groundwater body, but were situated in three different riparian zones. The input of O 2 into the groundwater as a result of the formation of excess air was found to be of the same order of magnitude as that resulting from the advection of river water, although the amount of excess air formed and the amount of O 2 delivered varied significantly among the riparian zones. The results suggest that the input of O 2 into groundwater as a result of excess air formation is controlled not only by the hydraulic conditions prevailing in the river and the groundwater, but also by the thickness of the confining bed at the top of the aquifer. The sandy gravel aquifer itself is too coarse to trap a significant amount of air during the water level rise. The clay layer confining the aquifer, however, acts as a barrier hindering the escape of air from the subsoil to the surface, and hence is likely to be a key factor controlling the trapping and dissolution of air in groundwater.

Description: Estimation of parameter values in hydrological models has gradually moved from subjective, trial-and-error methods into objective estimation methods. Translation of nature's complexity to bit operations is an uncertain process as a result of data errors, epistemic gaps, computational deficiencies, and other limitations, and relies on calibration to fit model output to observed data. The robustness of the calibrated parameter values to these types of uncertainties is therefore an important concern. In this study, we investigated how the hydrological robustness of the model-parameter values varied within the geometric structure of the behavioral (well-performing) parameter space with a depth function based on α shapes and an in-depth posterior performance analysis of the simulations in relation to the observed discharge uncertainty. The α shape depth is a non-convex measure that may provide an accurate and tight delimitation of the geometric structure of the behavioral space for both uni- and multimodal parameter-value distributions. WASMOD, a parsimonious rainfall-runoff model, was applied to six Honduran and one UK catchment, with differing data quality and hydrological characteristics. Model evaluation was done with two performance measures, the Nash-Sutcliffe efficiency and one based on flow-duration curves. Deep parameter vectors were in general found to be more hydrologically robust than shallow ones in the analyses we performed; model-performance values increased with depth, deviations to the observed data for the high-flow aspects of the hydrograph generally decreased with increasing depth, deep parameter vectors generally transferred in time with maintained high performance values, and the model had a low sensitivity to small changes in the parameter values. The tight delimitation of the behavioral space provided by the α shapes depth function showed a potential to improve the efficiency of calibration techniques that require further exploration. For computational reasons only a three-parameter model could be used, which limited the applicability of this depth measure and the conclusions drawn in this paper, especially concerning hydrological robustness at low flows.

Description: The cosmic-ray neutron probe measures soil moisture over tens of hectares, thus averaging spatially variable soil moisture fields. A previous paper described how variable soil moisture profiles affect the integrated cosmic-ray neutron signal from which depth-average soil moisture is computed. Here, we investigate the effect of horizontal heterogeneity on the relationship between neutron counts and average soil moisture. Observations from a distributed sensor network at a site in southern Arizona indicate that the horizontal component of the total variance of the soil moisture field is less variably in time than the vertical component. Using results from neutron particle transport simulations we show that 1-D binary distributions of soil moisture may affect both the mean and variance of neutron counts of a cosmic-ray neutron detector placed arbitrarily in a soil moisture field, potentially giving rise to an underestimate of the footprint average soil moisture. Similar simulations that used 1 and 2-D Gaussian soil moisture fields indicate consistent mean and variances of a randomly placed detector if the correlation length scales are short (〈˜30 m) and/or the soil moisture field variance is small (〈0.032 m 6 m -6 ). Taken together, these soil moisture observations and neutron transport simulations show that horizontal heterogeneity likely has a small effect on the relationship between mean neutron counts and average soil moisture for soils under natural conditions.

Description: Widespread disturbance within forested catchments typically increases runoff. However, following widespread fire in 1939 throughout south-east Australia Kuczera [1987] reported persistent reductions in runoff that were attributed to increased evapotranspiration from regenerating ‘ash’ forests. Kuczera projected ongoing reductions of water yield for ~150 years. In 2003 widespread fire in the headwaters of the Murray-Darling Basin (MDB) again stimulated extensive regeneration of ash forests, raising the prospect of subsequent water yield reductions. To understand the potential impact of the 2003 bushfires we re-evaluated yield reductions from three of the catchments originally studied by Kuczera using the same calibration period. We also used an expanded pre-fire calibration period (1908-1938) based on data not originally available to Kuczera. The trend of post-fire water yield that we observed in 1939-affected catchments is qualitatively consistent with Kuczera's projections, but the quantitative details were, as expected, sensitive to the pre-fire calibration period used. We then used a simplified method to examine a further five ash-dominated catchments affected by the 2003 fires. We report relative reductions in mean annual stream flow in all five catchments and a statistically significant (α=0.05) post-fire reduction in one of five catchments. Post-fire yield reductions during the austral summer (October-April) were greater in relative magnitude in all five catchments and were statistically significant (α=0.05) in three of five catchments. We conclude that a post-bushfire Kuczera-type response may be widespread in regenerating ash forests. On that basis we anticipate post-fire yield reductions in ash forests elsewhere and conclude that further reductions in stream flow are likely in the MDB for at least another decade.

Description: Drought triggers are patterns in hydro-climatic variables that herald upcoming droughts and form the basis for mitigation plans. This study develops a new method for identification of triggers for hydrologic droughts by examining the association between the various hydro-climatic variables and streamflows. Since numerous variables influence streamflows to varying degrees, Principal Component Analysis (PCA) is utilized for dimensionality reduction in predictor hydro-climatic variables. The joint dependence between the first two principal components, that explain over 98% of the variability in the predictor set, and streamflows is computed by a scale-free measure of association using asymmetric Archimedean copulas over two study watersheds in Indiana, USA, with unregulated streamflows. The M6 copula model is found to be suitable for the data and is utilized to find expected values and ranges of predictor hydro-climatic variables for different streamflow quantiles. This information is utilized to develop drought triggers for one-month lead time over the study areas. For the two study watersheds, soil moisture, precipitation and runoff are found to provide the fidelity to resolve amongst different drought classes. Combining the strengths of PCA for dimensionality reduction and copulas for building joint dependence allows the development of hydrologic drought triggers in an efficient manner.

Description: We present a unified asymptotic theory of rainfall extremes including annual maxima, excesses above high thresholds, and intensity-duration-frequency (IDF) curves that builds on previous findings and derive new non-asymptotic results. The analysis is based on stationary multifractal representations of rainfall and produces extensions of the familiar results from extreme value (EV) and extreme excess (EE) theories. The latter results apply to the T -yr maximum as and the excess above z as . By exploiting the scaling relationship among the distributions of rainfall intensity for different averaging durations d , the multifractal asymptotics include, in addition, results in the small-scale limits and with α 〉 0. In all cases the maximum distributions are of the generalized extreme value (GEV) type, but the index k depends on the limit considered. Multifractal models produce also asymptotic scaling results for the IDF curves. For the non-asymptotic case ( d and T finite), we obtain accurate approximations of the IDF curves and derive a semi-theoretical formula for the index k of the GEV model that best approximates the distribution of the annual maximum over a finite range of return-period intensities. The non-asymptotic analysis explains several observed deviations of rainfall extremes from the asymptotic predictions, such as the tendency of k to decrease as the averaging duration d increases and the tendency of the IDF curves to converge as d or the return period T increase.

Description: Remaining oil saturation established by waterflooding was measured in Indiana limestone in its original, water-wet state and under mixed-wet conditions established by adding organic acid to the oil phase. The porous plate technique was used to establish initial oil saturations ranging from S nwi = 0.23 to 0.93 under capillary-dominated conditions. For water-wet conditions, the residual oil saturation increased linearly with its initial saturation. In contrast, the remaining oil saturation under mixed-wet conditions, S nw , displayed three distinct regimes. First, S nw increased with its initial saturation up to S nwi = 0.58. Next, S nw decreased from S nwi = 0.58 to 0.76. Finally, S nw increased again as S nwi approached one. The non-monotonic dependence of S nw on S nwi at S nwi 〉 0.5 is well described by a concave-up quadratic function, and may be a salient feature of mixed-wet rocks.

Description: We present a general phenomenological formalism for the modeling of hydraulic head behaviour in naturally fractured aquifers. A non local in time version of the double porosity model is developed for Euclidean and fractal reservoirs. In the fractal case, time non-locality allows to find the geometric and topological factors responsible for subdiffusive behaviour in such heterogeneous environments. Opposite to other fractal models presented in the literature Chang and Yortsos [1990], our model include dead-ends-backbone interactions instead of matrix-fracture interactions with clear and well defined scaling exponents, thus giving a better characterization of the reservoir after such parameters are estimated. Applications to field tests are discussed. In particular, a distinctive short time head behaviour during well tests is found.

Description: The publicly available global discharge database is limited in spatial and temporal coverage. Although regional exceptions exist, the population of the database has declined over the past several years. As discharge is one of the most important parameters for modeling hydrological interactions, alternative measuring techniques must be sought. In the recent past, satellite altimetry has been investigated as an alternative for monitoring inland water level. In the present study, altimetry footprints in the vicinity of river gauging stations for the Amazon, Amur, Brahmaputra, Danube, Don, Mekong, Niger, Ob and Vistula rivers are analyzed for a functional relationship between the water level measurements from altimetry and discharge from the gauging stations. Such a functional relationship is conventionally established via a rating curve computed using simultaneous data. This study proposes a statistical approach based on quantile functions to infer this functional relation without the need for having synchronous datasets. The statistical approach provides the opportunity of extracting discharge values from altimetry data for rivers like the Mekong, Brahmaputra, Don and Vistula for which the discharge measurements at the selected gauges were made before the age of satellites. The algorithm is then validated over those rivers which do have discharge measurements available within periods of altimetry. Our validation shows that our algorithm is in the same quality range as the conventional approach. We are thus able to salvage pre-satellite altimetry discharge data and turn them into active use for the satellite altimetry time frame.

Description: Although some existing carbon markets are facing structural issues and economic difficulties in Europe have put a damper on the European Union emissions trading system, new carbon pricing initiatives are developing rapidly, and these initiatives could help slow down greenhouse gas emissions, according to a 29 May report from the World Bank.

Description: Tropical cyclone–generated storm surges are among the world's most deadly and costly natural disasters. The destructive nature of this hazard was clearly seen last fall, as Hurricane Sandy generated a devastating storm surge along the mid-Atlantic coast. The storm killed 147 people and caused approximately $50 billion in economic losses [Blake et al., 2012].

Description: Rifting of stable continents is a key element of plate tectonic cycles. In spite of numerous studies, the mechanism responsible for the initiation and evolution of rift valleys such as the East African Rift System (EARS) is still poorly understood, partly because most previous investigations focused on rift segments that were in the mature stage. Geodynamic modeling [ Huismans et al ., 2001] suggests that upwelling of the asthenosphere ubiquitously observed beneath mature rifts can either originate from thermal or dynamic anomalies in the deep mantle (active rifting) or be induced by thinning of the lithosphere from far-field stresses (passive rifting) [ Sengor and Burke , 1978].

Description: While satellite based remote-sensing has provided hydrologists with valuable new datasets, integration of such datasets in operational modeling systems is usually not straightforward due to spatial or temporal resolution issues or because remote sensing does not directly measure the hydrological quantities of interest. This is the case for satellite based radar-altimetry. River level variations can be tracked using radar altimetry at a temporal resolution between 10 and 35 days, depending on the satellite, but hydrologists are typically interested in river flows rather than levels and require predictions at daily or even sub-daily temporal resolutions. One way to exploit satellite radar altimetry is therefore to combine the data with hydrological models in a data assimilation framework. In this study, radar altimetry data from 6 ENVISAT virtual stations were assimilated to a routing model of the main reach of the Brahmaputra River driven by the outputs of a calibrated rainfall runoff model. The Extended Kalman Filter was used to update the routed water volumes for the years 2008 to 2010. Model performance was improved with the Nash-Sutcliffe model efficiency for daily discharge increasing from 0.78 to 0.84. The method uses very little in situ data and is easily implemented as an add-on to hydrological models and it therefore has the potential for large scale application to improve hydrological predictions in many river basins.

Description: Management of water temperatures in the Columbia River Basin (Washington) is critical because water projects have substantially altered the habitat of Endangered Species Act (ESA) listed species, such as salmon, throughout the basin. This is most important in tributaries to the Columbia, such as the Methow River, where the spawning and rearing life stages of these cold water fishes occurs. Climate change projections generally predict increasing air temperatures across the western United States, with less confidence regarding shifts in precipitation. As air temperatures rise, we anticipate a corresponding increase in water temperatures, which may alter the timing and availability of habitat for fish reproduction and growth. To assess the impact of future climate change in the Methow River, we couple historical climate and future climate projections with a statistical modeling framework to predict daily mean stream temperatures. A K -nearest neighbor algorithm is also employed to: (i) adjust the climate projections for biases compared to the observed record and (ii) provide a reference for performing spatiotemporal disaggregation in future hydraulic modeling of stream habitat. The statistical models indicate the primary drivers of stream temperature are maximum and minimum air temperature and streamflow and show reasonable skill in predictability. When compared to the historical reference time period of 1916-2006, we conclude that increases in stream temperature are expected to occur at each subsequent time horizon representative of the year 2020, 2040, and 2080, with an increase of 0.8 ± 1.9 °C by the year 2080.

Description: Thermal remote sensing methods for mapping evapotranspiration (ET) exploit the physical interconnection that exists between land-surface temperature (LST) and evaporative cooling, employing principles of surface energy balance (SEB). Unfortunately, while many applications in water resource management require ET information at daily and field spatial scales, current satellite-based thermal sensors are characterized by either low spatial resolution and high repeatability or by moderate/high spatial resolution and low frequency. Here we introduce a novel approach to ET mapping that fuses characteristics of both classes of sensors to provide optimal spatiotemporal coverage. In this approach, coarse resolution daily ET maps generated with a SEB model using geostationary satellite data are spatially disaggregated using daily MODIS (MODerate resolution Imaging Spectroradiometer) 1-km and bi-weekly Landsat LST imagery sharpened to 30-m. These ET fields are then fused to obtain daily ET maps at 30-m spatial resolution. The accuracy of the fused Landsat-MODIS daily ET maps was evaluated over Iowa using observations collected at 8 flux towers sited in corn and soybean fields during the Soil Moisture Experiment of 2002 (SMEX02), as well as in comparison with a Landsat-only retrieval. A significant improvement in ET accuracy (reducing errors from 0.75 to 0.58 mm/d on average) was obtained by fusing MODIS and Landsat data in comparison with the Landsat-only case, with most notable improvements when a rainfall event occurred between two successive Landsat acquisitions. The improvements are further evident at the seasonal timescale, where a 3% error is obtained using Landsat-MODIS fusion vs. a 9% Landsat-only systematic underestimation.

Description: Graphite is known to be a low-friction material, and rocks rich in graphite are often found in fault zones. Oohashi et al . conducted laboratory studies to determine how much graphite is needed to reduce the frictional strength of a fault. Their experiments included samples with various mixtures of graphite and quartz, as well as pure quartz and pure graphite, and they covered large displacements (up to 100 meters), a range of slip rates (from 200 micrometers per second to 1.3 meters per second), and a range of shear strains (up to several tens of thousands).

Description: The U.S. National Academy of Sciences (NAS) recently announced its 2013 class of new members. They include Gregory Asner , faculty scientist in the Department of Global Ecology at the Carnegie Institution for Science, Stanford, Calif.; Mark Cane , G. Unger Vetlesen Professor of Earth and Climate Sciences in the Department of Earth and Environmental Sciences at the Lamont-Doherty Earth Observatory of Columbia University, Palisades, N. Y.; Kenneth Farley , W. M. Keck Foundation Professor of Geochemistry and chair of the Division of Geological and Planetary Sciences, California Institute of Technology (Caltech), Pasadena; Terry Plank , professor in the Department of Earth and Environmental Sciences at Lamont-Doherty; and John Seinfeld , Louis E. Nohl Professor in the Department of Chemical Engineering at Caltech.

Description: The inner magnetosphere ring current, which circles the Earth a few Earth radii above the surface, consists of energetic ions and electrons and plays an important role in the space environment. During geomagnetic storms the flow in the ring current rises dramatically. The behavior of the ring current and other features of the inner magnetosphere depend strongly on conditions in other regions of the magnetosphere. The small scale of the particle dynamics that drive the ring current, compared to the vast spatial scale of the entire magnetosphere, makes it difficult to represent both the nuance of the inner magnetosphere and the full scope of the magnetospheric system.

Description: The stratigraphic record, the sequential layers of sediment that geologists use to reconstruct the history of a landscape, has been described as “more gaps than record.” The record, laid down over time as sediment settles out from flowing water, does not grow consistently. Pauses in sediment deposition can leave gaps, and periods of heightened erosion can wipe out sections. Although attempts have been made to identify the processes that control the completeness of the stratigraphic record, early analyses relied on parameters (such as the long-term sediment accumulation rate) that are not first-order physical landscape processes.

Description: With increasing frequency, we are hearing reports and declarations about the real and impending impacts associated with changing hydrologic and physical systems. Droughts are forecasted to expand and persist, storms are increasing in frequency and intensity, and reservoirs are draining, filling up with sediment, or overflowing. The obvious conclusion is that we are in a changing, dynamic time regarding water, weather, and climate.

Description: Despite repeated reassurances from Obama administration officials that it is unlikely that a near-Earth object (NEO) could cause catastrophic damage on Earth anytime over the next several hundred years, members of the U.S. House of Representatives Committee on Science, Space, and Technology kept raising “what if” questions at a 19 March hearing about threats from space.

Description: Mapping extreme snowfalls in mountainous areas is important for directing resources to keep roads clear and manage avalanche risk. But data in mountainous areas are sparse, with instruments often located in valleys far from areas of concern, and historical instrumental records are generally incomplete. Scientists must therefore extrapolate and interpolate from observations to estimate snowfall amounts over a region.

Description: From efforts to help scientists remotely monitor meteorites hitting the Moon to campaigns to count craters on raw images of the asteroid Vesta, creative strategies to utilize the public's ability to collect and analyze data are being employed for a variety of lunar and planetary science projects. According to speakers at a session called “Rising to the challenge: Improving public understanding of science in the next decade,” held at the 44th annual Lunar and Planetary Science Conference in The Woodlands, Tex., from 18 to 22 March, these citizen science projects tap into public enthusiasm about worlds beyond our own.