1,720,972 research outputs found
A review on rainfall data resolution and its role in the hydrological practice
No full textData collected by gauges represent a fundamental force in most hydrological studies. On the basis of sensor type and recording system, such records are characterized by different aggregation time, ta. In this review paper, a comprehensive rainfall database of rain gauge networks operative worldwide is used to determine the temporal evolution of ta . As a second step, issues related to the limited and heterogeneous temporal resolution of rainfall data are discussed with regard to avoiding possible errors in the analysis of historical series. Particular attention is focused on quantifying the effects on the estimation of extreme rainfalls that play a crucial role in designing hydraulic structures. To this aim, algebraic relations for improving a correct determination of extreme rainfall are also provided
Ragguaglio areale delle precipitazioni intense in Umbria
No full textIl presente studio nasce da una convenzione stipulata tra la Regione Umbria e il Dipartimento di Ingegneria Civile ed Ambientale (DICA) dell’Università degli Studi di Perugia.
Il principale scopo dello studio consiste nell’individuazione di una legge empirica di ragguaglio areale delle piogge, specificamente calibrata sul territorio umbro, valida per tutte le durate e per tutte le estensioni areali di interesse regionale (fino a circa 6000 Km2). Per raggiungere tale obiettivo finale, occorre preliminarmente perseguire anche i seguenti obiettivi secondari:
- analizzare i dati pluviometrici con tempo di aggregazione pari a 1 minuto relativi alle stazioni gestite dalla Regione Umbria, con particolare riferimento ai dati acquisiti nel corso degli ultimi anni, determinando e validando le altezze (o spessori) massime annuali di pioggia per durate pari a 5, 10, 15, 20, 30, 40, 60, 180, 360, 720, 1440, 2160 e 2880 minuti;
- determinare serie pluviometriche medie areali, per superfici di estensione fino a circa 6000 Km2;
- calcolare i fattori empirici di ragguaglio areale delle precipitazioni per tutte le durate analizzate.
La conoscenza dei cosiddetti fattori di riduzione areale della pioggia (ARF, acronimo dei termini inglesi Areal Reduction Factor) risulta di fondamentale importanza nella pratica idrologica. Infatti, i modelli matematici di trasformazione pioggia-portata utilizzati comunemente per la stima di una portata di progetto nella sezione di chiusura di un bacino
idrografico necessitano della conoscenza della precipitazione di progetto media areale sul bacino stesso, ma in genere l’informazione di cui si dispone è di natura puntuale, derivante dalle misure effettuate dai pluviometri. Sono proprio gli ARF a consentire la complessa trasformazione delle informazioni pluviometriche da puntuali ad areali. Tuttavia, le
relazioni che consentono di determinare gli ARF presenti nella letteratura scientifica sono molto diverse in funzione del territorio nel quale sono state calibrate. Quest’ultimo aspetto costituisce la principale motivazione che ha condotto alla stipula della convenzione sopra ricordata. Infatti, non esiste al momento alcuna relazione specificamente utilizzabile nel territorio regionale umbro, ottenuta da analisi condotte sulle precipitazioni osservate dai pluviometri della regione.
In quanto segue, dopo un’ampia descrizione del significato del fattore di riduzione areale, vengono prima presentate le principali relazioni presenti nella letteratura scientifica e poi illustrate le modalità di analisi dei dati che hanno consentito lo sviluppo della prima relazione empirica specifica per l’Umbria
Long-term analysis of rainfall-induced landslides in Umbria, central Italy
No full textAnalyses of historical records of landslides and climate variables are useful tools to search for correlations between damaging landslide events and their triggers. In this work, we investigate the temporal and geographical relationships between two long-term historical series of catalogued landslide occurrences and daily rainfall data in Umbria, a central Italian region, from 1928 to 2001. Moreover, we search for changes in the frequency and density of landslides, and in the characteristics of the associated rainfall events. Using a consolidated approach, partially modifed, we fnd that the rainfall events that have produced rainfall-induced landslides in Umbria changed in space and time during observation period and between two considered sub-periods (1928–1975 and 1976–2001). In particular, we fnd that: (i) the monthly distribution of landslides associated with rainfall events is quite diferent than that of all landslides in the regional catalogue; (ii) the spatial and temporal distribution of REL changed from the older (most events occurred in winter) to the recent period (most events occurred in autumn); (iii) the recent most rainfall events associated with landslides are characterized by a lower cumulated rainfall and a shorter duration, sign of an increased propensity of the regional territory to produce landslides over time
Simplified method to derive a pedotransfer function for average field saturated hydraulic conductivity with limited data-set
No full textSaturated hydraulic conductivity, Ks, is highly variable in space. It exhibits seasonal variability (Bormann and Klaassen 2008), scale dependency with regards to the volume of soil investigated (Lai and Ren 2007) and its value
is affected by the measurement technique used for in-situ exploration (Morbidelli et al. 2017). Measurements of Ks were performed in the Hydrological Open Air Laboratory (HOAL) catchment (Blöschl et
al. 2016), Petzenkirchen, Austria, by means of Double-Ring Infiltrometer (DRI). The DRI measurements were carried out in 136 locations, grouped in 12 stations, and in each station measurements distant 3m one another were
performed. In order to study the uncertainty of mean Ks, Ks, as a function of both the number of measurements and the size of the sampled area, an analysis on the observed values of the station which provided the largest data-set was performed. With a minimum of 6 measurements the amplitude of the 95% confidence interval of the geometric mean decreases to a factor of 1.9, regardless of the sampled areal extent and the sample size. This tolerance value is consistent with Ahmed et al. (2015), where a reduction factor of 2.5–3.25 was considered as threshold for the determination of a minimum number of measurements.
To develop a pedotransfer function (PTF) for the HOAL catchment, soil texture, organic matter content and average slope were considered as predictor variables for the determination of the dependent variableKs. On the basis of the previous analysis, the observed Ks local values were averaged by 6 measurements at a time. Due to the presence of multicollinearity in the matrix of regressors, the Ridge regression technique was applied. The prediction ability is quantified by the index of agreement d = 0.91. A map of Ks for the HOAL is also produced, which shows a pattern similar to the soil types map of the catchment
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
A plot-scale uncertainty analysis of saturated hydraulic conductivity of a clay soil
No full textSimulating soil hydrological processes at the plot or field scale requires using spatially representative values of the saturated soil hydraulic conductivity, Ks. Sampling campaigns should yield a reliable mean of Ks with a sustainable workload since measuring Ks at many points is challenging. Uncertainty analysis can be used to determine the lowest number of measurements that yield a mean Ks value with a specified accuracy level. Potential and limitations of this analysis were tested in this investigation for different extents of the sampled area and sampling densities. A clay soil was sampled intensively on two plots (plot area = 44 m2), two dates and using both small (0.15 m in diameter) and large (0.30 m) rings. With the small rings, intensively sampling an appropriate portion of the total plot area should be enough to establish the number of measurements yielding a certain accuracy level for the entire plot since this level remained nearly constant when the same number of measurements was performed on larger areas. Moreover, for these areas, the spatial resolution of the measurements did not influence appreciably the width of the confidence interval of the mean Ks value. However, working with larger rings was recommended since, in this case, the sampled area did not affect at all normalized confidence levels that, in addition, varied only a little with the number of the considered measurements of Ks. In practice, characterizing the plots required about 20 and 10 measurements with the smaller and the larger rings, respectively. The uncertainty analysis appears promising to plan practically sustainable soil sampling campaigns
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
- …
