1,721,103 research outputs found
Physically based modeling in catchment hydrology at 50: Survey and outlook
Full text linkIntegrated, process-based numerical models in hydrology are rapidly evolving, spurred by novel theories in mathematical physics, advances in computational methods, insights from laboratory and field experiments, and the need to better understand and predict the potential impacts of population, land use, and climate change on our water resources. At the catchment scale, these simulation models are commonly based on conservation principles for surface and subsurface water flow and solute transport (e.g., the Richards, shallow water, and advection-dispersion equations), and they require robust numerical techniques for their resolution. Traditional (and still open) challenges in developing reliable and efficient models are associated with heterogeneity and variability in parameters and state variables; nonlinearities and scale effects in process dynamics; and complex or poorly known boundary conditions and initial system states. As catchment modeling enters a highly interdisciplinary era, new challenges arise from the need to maintain physical and numerical consistency in the description of multiple processes that interact over a range of scales and across different compartments of an overall system. This paper first gives an historical overview (past 50 years) of some of the key developments in physically based hydrological modeling, emphasizing how the interplay between theory, experiments, and modeling has contributed to advancing the state of the art. The second part of the paper examines some outstanding problems in integrated catchment modeling from the perspective of recent developments in mathematical and computational science
Catchment-scale Richards equation-based modeling of evapotranspiration via boundary condition switching and root water uptake schemes
Full text linkIn arid and semiarid climate catchments, where annual evapotranspiration (ET) and rainfall are typically comparable, modeling ET is important for proper assessment of water availability and sustainable land use management. The aim of the present study is to assess different parsimonious schemes for representing ET in a process-based model of coupled surface and subsurface flow. A simplified method for computing ET based on a switching procedure for the boundary conditions of the Richards equation at the soil surface is compared to a sink term approach that includes root water uptake, root distribution, root water compensation, and water and oxygen stress. The study site for the analysis is a small pasture catchment in southeastern Australia. A comprehensive sensitivity analysis carried out on the parameters of the sink term shows that the maximum root depth is the dominant control on catchment-scale ET and streamflow. Comparison with the boundary condition switching method demonstrates that this simpler scheme (only one parameter) can successfully reproduce ET when the vegetation root depth is shallow (not exceeding approximately 50 cm). For deeper rooting systems, the switching scheme fails to match the ET fluxes and is affected by numerical artifacts, generating physically unrealistic soil moisture dynamics. It is further shown that when transpiration is the dominant contribution to ET, the inclusion of oxygen stress and root water compensation in the model can have a considerable effect on the estimation of both ET and streamflow; this is mostly due to the water fluxes associated with the riparian zone. Key Points: Simple, parsimonious ET schemes for integrated hydrological models are assessed Boundary condition switching is suitable only for shallow root depths Oxygen stress and root water compensation influence riparian zone ET dynamics
Control of coupling mass balance error in a process-based numerical model of surface-subsurface flow interaction
Full text link© 2015. American Geophysical Union. All Rights Reserved.A process-based numerical model of integrated surface-subsurface flow is analyzed in order to identify, track, and reduce the mass balance errors affiliated with the model's coupling scheme. The sources of coupling error include a surface-subsurface grid interface that requires node-to-cell and cell-to-node interpolation of exchange fluxes and ponding heads, and a sequential iterative time matching procedure that includes a time lag in these same exchange terms. Based on numerical experiments carried out for two synthetic test cases and for a complex drainage basin in northern Italy, it is shown that the coupling mass balance error increases during the flood recession limb when the rate of change in the fluxes exchanged between the surface and subsurface is highest. A dimensionless index that quantifies the degree of coupling and a saturated area index are introduced to monitor the sensitivity of the model to coupling error. Error reduction is achieved through improvements to the heuristic procedure used to control and adapt the time step interval and to the interpolation algorithm used to pass exchange variables from nodes to cells. The analysis presented illustrates the trade-offs between a flexible description of surface and subsurface flow processes and the numerical errors inherent in sequential iterative coupling with staggered nodal points at the land surface interface, and it reveals mitigation strategies that are applicable to all integrated models sharing this coupling and discretization approach
Hydrologic impacts of surface elevation and spatial resolution in statistical correction approaches: case study of Flumendosa Basin, Italy
Full text linkThe role of surface elevation and spatial resolution in statistical correction approaches for temperature and precipitation forcing
is investigated using four global climate model (GCM) and regional climate model (RCM) combinations. A Mediterranean basin characterized by steep orography and prone to extreme flooding is chosen as a test case. For this aim, precipitation is statistically downscaled
using a parametric scheme for bias correction and high-resolution downscaling and a widely used nonparametric approach, with nominal
resolution equal to that of the GCM/RCM. Temperature fields are reprojected from climate model to terrain elevation at high resolution. The
response of the basin in terms of discharge, actual evapotranspiration, and leakage is simulated using the TOPographic Kinematic APproximation and Integration (TOPKAPI-X) model from 1951 to 2099 and at multiple spatial scales. To investigate the role of orography, simulations are run applying the downscaling schemes on a flat terrain. The results show that, independently of the size of the basin, the
elevation factor minimally affects the simulated hydrological response, whereas the effect of the spatial resolution of downscaled precipitation fields on the hydrological budget components is significant, and depends on the catchment size
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Machine Learning vs. Physics-Based Modeling for Real-Time Irrigation Management
Full text linkReal-time monitoring of soil matric potential has now become a common practice for
precision irrigation management. Some crops, such as cranberries, are susceptible
to both water and anoxic stresses. Excessive variations in soil matric potential in
the root zone may reduce plant transpiration, due to either saturated or dry soil
conditions, thereby reducing productivity. A timely supply of the right amount of water is,
therefore, fundamental for efficient irrigation management. In this paper, we compare
the capabilities of a machine learning-based model and a physics-based model to
predict soil matric potential in the root zone. The machine learning model is a random
forest algorithm, while the physics-based model is a two-dimensional solver of Richards
equation (HYDRUS 2D). After training and calibration on a dataset collected in a cranberry
field located in Québec (Canada), the performance of the two models is evaluated for
30 different time frames of 72-h soil matric potential forecasts. The results highlight
that both models can accurately forecast the soil matric potential in the root zone. The
machine learning-based model can achieve better performance when compared to the
physics-based model, but forecasting accuracy decreases rapidly toward the end of the
72-h lead time, while the error for the Richards equation-based model does not increase
with time and remain small compared to the typical measurement error
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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