1,720,987 research outputs found
Accounting for the spatial range of soil properties in pedotransfer functions
Get PDFPedotransfer functions (PTF) are widely used in soil hydraulic property modelling. Accounting for spatial structures of soil properties for improving the model performance of PTF is increasingly discussed. To understand how model performance varies when PTF are trained with samples of different spatial structure of the input data, we developed 12 ePTF (ensemble PTF) with data input from differently sized spatial domains to predict field capacity (FC) and wilting point (WP) of agriculturally used soils in Austria. The training domains generally had diameters equal to or larger than the spatial range of the explaining variables (bulk density BD, organic carbon content OC, Sand, Silt, and Clay) and the response variable (FC or WP). A stepwise regression technique was used to train the ePTF, and both bootstrap and random sampling were used to evaluate the uncertainties of the various ePTF. We found that, a training domain considerably larger than the spatial range of the input variables did not help develop a roubust ePTF, particularly when applied on relatively larger scales, independent of their performances during the training stage. We conclude that, covering additional heterogeneous samples from outside of the spatial range of the input variables does not ensure an enhanced prediction capability of ePTF. Also, it might be worth paying more attention to the spatial structure of the predicted variable when its spatial range might be expected to be quite different from the predictors. This would have an implication for guiding sampling practices
Comparison of hydrological models with different complexity in the Hydrological Open Air Laboratory in Austria
Get PDFHydrologische Modelle sollen ein Einzugsgebiet mit allen möglichen Wechselwirkungen ganzheitlich abbilden. Dabei gilt es auszuloten, welche Komponenten näher betrachtet werden sollen und welche zu vernachlässigen sind. Das Ziel dieser Arbeit ist die Untersuchung der Niederschlags-Abfluss-Prozesse im 66 ha großen Einzugsgebiet des HOAL (Hydrological Open Air Laboratory) im niederösterreichischen Petzenkirchen, als auch in kleineren Teileinzugsgebieten mit jeweils unterschiedlichen Abflussmechanismen. Dabei werden zwei verschiedene Modellkonzepte auf Basis des HBV-Modells angewandt und anschließend verglichen. Es handelt sich dabei, einerseits um das lumped TUWmodel und andererseits, um das flächendetaillierte HBV-Modell.Es werden die Messdaten von 2013 bis 2020 herangezogen. In einem ersten Schritt werden die zur Verfügung gestellten Messdaten aufbereitet, um sie in weiterer Folge als Inputdaten in den Modellen verwenden zu können. Das lumped TUWmodel wird mit einer zeitlichen Auflösung von einer Stunde angewandt. Jedes Teileinzugsgebiet muss dabei in einem eigenen Rechenlauf simuliert werden. Mit Hilfe eines Optimierungsalgorithmus (DEoptim in R) werden die besten Parameter für das gesamte Einzugsgebiet, als auch für jedes der 11 Teileinzugsgebiete gesucht und auf einer, davon unabhängigen Messperiode validiert. Auf Grundlage dieser Parameter wird ein vergleichbares flächendetailliertes HBV-Modell erstellt. Dieses wird in 15-minütiger zeitlicher und 5,0 x 5,0m räumlicher Auflösung angewandt. Bei diesem Modellkonzept werden alle Teileinzugsgebiete zeitgleich in einem Rechenlauf simuliert. Um die Qualität der Modelle beurteilen zu können, werden statistische Kennwerte herangezogen. Diese sind die Nash-Sutcliffe-Effizienz (NSE) und der Volumenfehler (VE). Dabei liefert das lumped TUWmodel mit den dafür optimierten Parametern bei diesen statistischen Kennwerten die besseren Ergebnisse. Es können NSE zwischen -0,14 bei Q1 und 0,68 bei MW, beim flächendetaillierten HBVModell zwischen -6,9 bei Frau2 und 0,43 bei MW erreicht werden.Anschließend wird mit den beiden Modellen eine Variantenstudie durchgeführt. Als Szenario kommt die flächendeckende Aufforstung des HOAL Einzugsgebietes zur Anwendung. Die Simulationsergebnisse zeigen bei beiden Modellkonzepten einen Anstieg des Basisabflusses in allen Teileinzugsgebieten. Zugleich verringert sich die Häufigkeit und Intensität der Spitzenabflüsse. Das weist darauf hin, dass der Wald als ausgleichendes Medium im Wasserkreislauf des HOAL fungiert.Das flächendetaillierte HBV-Modell erzielt schlechtere Simulationsergebnisse als das lumped TUWmodel. Beim flächendetaillierten HBV-Modell gibt es viele Flächen bei denen der Abfluss nicht gemessen werden kann. Diese sollten auf jeden Fall anders parametrisiert werden. Außerdem sollte auch die Modellstruktur besser an das HOAL und dessen unterschiedliche und komplexen Abflussmechanismen angepasst werden. Eine Herausforderung stellen auch kleine Abflüsse und ein Austrocknen einzelner Teileinzugsgebiete dar. Unter diesen Umständen eignet sich die abgeschlossene Betrachtungsweise der Teileinzugsgebiete mit dem lumped TUWmodel besser für eine hydrologische Modellsimulation im HOAL.Hydrological models are supposed to represent rainfall-runoff processes in a catchment with all possible interactions in a very realistic way. It is important to determine which components should be considered and which could be ignored. In this thesis the aim is to simulate the rainfall-runoff processes in the 66 ha large catchment of the HOAL (Hydrological Open Air Laboratory) in Petzenkirchen, Lower Austria, as well as in its tributaries, each featuring different runoff generation mechanisms. Two different model concepts, based on the continuous, conceptual HBV-model are applied and compared such as the lumped TUWmodel and the spatially distributed HBV-model.In a first step, the available measured data for the time period 2013-2020 for precipitation, air temperature and runoff are prepared in order to use them as input data for the models. The lumped TUWmodel is used with a temporal resolution of one hour. Each subcatchment is simulated in a separate computational run. For the lumped TUWmodel, with the help of an optimization algorithm (DEoptim in R) the best parameters for the HOAL catchment and for each of the 11 subcatchments are identified. Afterwards the parameters are validated on an independent measurement period.A spatially distributed HBV-model is created using exactly same parameters. It is applied at 15-minute temporal and 5.0 x 5.0m spatial resolution. In this model concept, all subcatchments are simulated simultaneously in only one computational run. In order to evaluate and compare the quality of the two different models goodness-of-fit measures are defined. These are the Nash-Sutcliffe Efficiency (NSE) and the Volume Error (VE). The lumped TUWmodel with the optimized parameters produces the better results. Nash-Sutcliffe Efficiencies between -0,14 for Q1 and 0,68 for MW can be achieved with the lumped TUWmodel and between -6,9 for Frau2 and 0,43 for MW using the spatially distributed HBV-model.Finally, a scenario analysis is performed with the two different models. As a scenario, the reforestation of the catchment area is assumed. The simulation results show an increase in baseflow in all subcatchment areas for both model concepts. At the same time, the occurrence and intensity of peak flows decreases. It could be shown that the forest acts as a buffer zone in the water cycle of the HOAL.The spatially distributed HBV-model generates worse simulation results in HOAL than the simpler lumped TUWmodel. In the spatially distributed HBV-model there are a lot of areas where the runoff cannot be measured. These areas should be parameterized differently in any case. In addition, the model structure should also be adapted to the HOAL and its different and complex runoff mechanisms. A challenge for rainfall-runoff modelling in the HOAL using the spatially distributed HBV-model is small runoff rates and the drying out of its tributaries. Under these circumstances, the lumped method is better qualified for a hydrological model simulation in HOAL
Agricultural intensification vs. climate change: what drives long-term changes in sediment load?
Get PDFProject Co-ordinators: Dr. Jose Alfonso Gómez Calero (Instituto de Agricultura Sostenible (IAS-CISC), Dr. Weifeng Xu (Fujian Agriculture and Forest University, FAFU). -- Trabajo desarrollado bajo la financiación del proyecto “Soil Hydrology research platform underpinning innovation to manage water scarcity in European and Chinese cropping Systems” (773903), coordinado por José Alfonso Gómez Calero, investigador del Instituto de Agricultura Sostenible (IAS).Climate change and agricultural intensification are expected to increase soil erosion and sediment production from arable land in many regions. However, to date, most studies have been based on short-term monitoring and/or modeling, making it difficult to assess their reliability in terms of estimating long-term changes. We present the results of a unique data set consisting of measurements of sediment loads from a 60 ha catchment – the Hydrological Open Air Laboratory (HOAL) – in Petzenkirchen, Austria, which was observed periodically over a time period spanning 72 years. Specifically, we compare Period I (1946–1954) and Period II (2002–2017) by fitting sediment rating curves (SRCs) for the growth and dormant seasons for each of the periods. The results suggest a significant increase in sediment loads from Period I to Period II, with an average of 5.8 ± 3.8 to 60.0 ± 140.0 t yr−1. The sediment flux changed mainly due to a shift in the SRCs, given that the mean daily discharge significantly decreased from 5.0 ± 14.5 L s−1 for Period I to 3.8 ± 6.6 L s−1 for Period II. The slopes of the SRCs for the growing season and the dormant season of Period I were 0.3 and 0.8, respectively, whereas they were 1.6 and 1.7 for Period II, respectively. Climate change, considered in terms of rainfall erosivity, was not responsible for this shift, because erosivity decreased by 30.4 % from the dormant season of Period I to that of Period II, and no significant difference was found between the growing seasons of periods I and II. However, the change in sediment flux can be explained by land use and land cover change (LUCC) and the change in land structure (i.e., the organization of land parcels). Under low- and median-streamflow conditions, the land structure in Period II (i.e., the parcel effect) had no apparent influence on sediment yield. With increasing streamflow, it became more important in controlling sediment yield, as a result of an enhanced sediment connectivity in the landscape, leading to a dominant role under high-flow conditions. The increase in crops that make the landscape prone to erosion and the change in land uses between periods I and II led to an increase in sediment flux, although its relevance was surpassed by the effect of parcel structure change under high-flow conditions. We conclude that LUCC and land structure change should be accounted for when assessing sediment flux changes. Especially under high-flow conditions, land structure change substantially altered sediment fluxes, which is most relevant for long-term sediment loads and land degradation. Therefore, increased attention to improving land structure is needed in climate adaptation and agricultural catchment management.This work has been supported by the SHui (Soil Hydrology research platform underpinning innovation to manage water scarcity in European and Chinese cropping systems) project within the Horizon 2020 Research and Innovation action of the European Community (project no. 773993), the Austrian Science Funds (FWF; project no. W1219-N28), and the TU Wien Risk network.Peer reviewe
Comparison of two isotopic hydrograph separation methods in the Hydrological Open Air Laboratory, Austria
Get PDFExploring the contributions of new and old water to runoff during precipitation events in agricultural catchments is essential for understanding runoff generation, solute transport, and soil erosion. The aim of this study was to investigate the variability in the isotopic composition of precipitation and runoff in the 66 ha agricultural catchment in Austria, in the Hydrological Open Air Laboratory (HOAL), in order to compare two isotope hydrograph separation methods. The classical two-component (IHS) and the ensemble hydrograph separation (EHS) were applied to multiple large events in May–October of 2013–2018 using δ18O and δ2H. The peak flow new water contributions obtained by IHS were compared with the average new water fraction from EHS. The average new water fraction calculated with EHS based on regular weekly sampling was close to zero, which can be explained by the large diffuse groundwater discharge into the stream between the events. When only investigating events with high temporal resolution sampling, the results suggest that EHS provided average new water fractions during peak flows (0.46 ± 0.04 for δ18O, 0.47 ± 0.03 for δ2H) that were close to the averages obtained by IHS (0.47 for δ18O, 0.50 for δ2H). New water fractions tended to be higher for larger rainfall intensities. High peak flow new water fractions could be explained by the agricultural land use and soils with low permeability promoting overland flow generation and by some of the tile drainage systems contributing to the delivery of water. In conclusion, a weekly sampling frequency was not sufficient in the HOAL but instead high-resolution sampling during events was necessary to estimate the average new water contributions during events. While EHS may be a more robust approach compared to IHS, as it relaxes some of the assumptions of IHS, IHS can provide information on the variability of new water contributions of individual events
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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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