1,720,956 research outputs found
Bilancio Idrico del Lago Trasimeno
No full textIl lavoro riassume i risultati delle ricerche idrologiche ed idrogeologiche condotte dagli autori sul Lago Trasimeno, nel quadro delle attuali variazioni climatiche. Il Trasimeno è un lago privo di emissari naturali, oggi con superficie media di circa 122 km2 e profondità massima attorno a 5.2 m. L’area del bacino imbrifero che drena nel lago è appena 2.2 volte maggiore dell’area dello specchio lacustre. Per questi motivi il Trasimeno è caratterizzato da una marcata variabilità dei livelli e del volume d’acqua immagazzinato, strettamente legata alla variabilità delle precipitazioni: ciò, anche a causa della piccola profondità, costituisce da sempre un grave problema per le popolazioni rivierasche. I dati a disposizione e la modellizzazione della trasformazione afflussi deflussi (periodo 1984 – 2006) indicano che:
- Il coefficiente di deflusso globale medio annuo del bacino è attorno a 0.24 - 0.25.
- La somma dei prelievi e dell’evaporazione dal Lago è attorno a 135 Mm3/anno. I prelievi effettivi dovrebbero essere al più attorno a 10 Mmc/anno, con una diminuzione negli ultimi anni.
- Le precipitazioni nell’insieme mostrano un certo decremento, anche se non marcato come quello di altre località umbre (50 mm nei mesi invernali del periodo 1984 – 2006 rispetto al periodo 1966 – 1984).
- L’effetto della diminuzione della piovosità, esaltato dall’aumento della temperatura, è particolarmente importante se si considera che nella realtà la diminuzione media è dovuta all’addensarsi di anni con diminuzione notevolmente inferiore alla diminuzione media, e che questa è dello stesso ordine di grandezza dei prelievi.
- Le simulazioni del modello matematico indicano che per combattere efficacemente i problemi, ciclici, di livelli bassi e di aumento della salinità e del connesso rischio di deterioramento della qualità dell’acqua, è necessario apportare al Lago circa 15 Mmc/anno.
- Se il trend climatico rilevato dovesse continuare, e se gli scenari più gravi dell’IPCC dovessero avverarsi, l’apporto/risparmio di 15 Mm3anno sopra stimati non sarebbero più sufficienti ad impedire un marcato decremento medio della superficie e dei livelli del Trasimeno.
- Per migliorare le conoscenze sul Lago è necessario migliorare notevolmente la qualità della rete di misura dei dati idro-meteorologici, avendo particolare cura della continuità dei dati
L’EVAPORAZIONE DAI LAGHI DELL’ITALIA CENTRALE: ALCUNE CONSIDERAZIONI A PARTIRE DAL CAMPO SPERIMENTALE DI SAN SAVINO (LAGO TRASIMENO, UMBRIA)
No full textImpact of the present climatic trends on the discharge of Bagnara spring (Umbria - Marche Apennines, Italy)
No full textAnalysis of the most reliable meteorological datasets for Central Italy reveal that most of the series have trends. Their presence and intensity vary according to statistical technique, to quality of data and geographical location, but the general picture is quite clear: in practice, all stations showing significant trends report a decrease in rainfall and an increase in temperature. Temperature increase and rainfall decrease inevitably reduce the water yield of hydrological systems: indeed, analyses of discharge data series of some hydrogeological systems in Central Italy show negative trends. Although in some systems it is not easy to define in which proportions this trend is to be related to climatic variations or to exploitation or land use, there are some systems – particularly mountain catchments and springs - which can be considered as not influenced by human activity and which show a decrease in yield over the last 40-50 years. One of these systems is Bagnara Spring which has been studied in order to obtain some reasonable scenario about the discharges during the next 30 years, assuming that the climatic trend of the last decades will persist. Bagnara spring is fed by the Monte Pennino anticline, which is a typical Apenninic structure, an east-vergent asymmetric anticline, with a main thrust structure and some secondary thrusts on the eastern slope, and back thrusts structures on the western slope. The rocks outcropping in the area belong to the Umbria-Marche geological sequence, which is mainly made of limestone formations within which some marl formations occur. According to the geological setup, the potential recharge area of the spring is about 7.5 km2 wide. In spite of their poor quality, the analysis of the meteorological data in the area indicates that during the period 1982-2009 the water surplus (defined as the difference between rainfall and evapotranspiration) decreased of about 15 – 20 % compared to the 1954 – 1981 period. In order to have an idea about the future discharges of the spring, a set of lumped models of the rain-discharge process transformation was applied. All the models were on a monthly basis. Under the assumption that the present trend will continue and in spite of their different performance, the models indicate a decrease of the discharges higher than the decrease of the water surplus. This should be taken in account in the future water management plans. Sounder results and better modeling could be obtained if the meteorological data were more reliable: it is imperative that a reliable data net for the measurement of evaporation, piezometric heads, rain, snow and temperature is establishe
Climatic change and water resources in Central Italy: an update
No full textIn the last hundred years the average global atmospheric temperature has risen by about 0.6°C - 1°C. In southern Europe and the Mediterranean area, this rise is associated with higher frequency and duration of droughts, and a general decrease of average yearly precipitation. This paper regards in particular Central Italy, where the trends detected in instrumental series of precipitation and temperature show that in all the stations with a statistically significant trend there is an increase in mean annual temperature (gradients up to +0.01°C/year) and a decrease in annual precipitation, with linear gradients up to -7 mm/year. Climate change greatly influences the hydrogeological processes regulating both groundwater and surface water availability. Evidence of this influence is represented by the statistically significant negative trends found in the mean annual and monthly yields of some important hydrologic and hydrogeologic systems. Negative effects can also be observed on lake systems, on which climatic changes induce decreases in levels and outlet discharges, amplified by constantly increasing withdrawals.
Within the framework of this general picture, the present work presents some results regarding the impact of the going on climatic trend on two specific systems
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
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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