1,720,958 research outputs found
Climatology of snow depth and water equivalent measurements in the Italian Alps (1967-2020)
Full text linkA climatology of snow water equivalent (SWE) based on data collected at 240 gauging sites was performed for the Italian Alps over the 1967-2020 period, when Enel routinely conducted snow depth and density measurements with homogeneous methods. Six hydrological sub-regions were investigated spanning from the eastern Alps to the western Alps at altitudes ranging from 1000 to 3000 m a.s.l. Measurements were conducted at fixed dates at the beginning of each month from 1 February to 1 June and on 15 April. To our knowledge, this is the most comprehensive and homogeneous dataset of measured snow depth and density for the Italian Alps. Significant decreasing trends over the years at all fixed dates and elevation classes were identified for both snow depth, equal to - 0.12 +/- 0.06 m per decade, and snow water equivalent, equal to - 51 +/- 37 mm per decade, on average in the six macro-basins we selected. The analysis of bulk snow density data showed a temporal evolution along the snow accumulation and melt season, but no altitudinal trends were found. A Moving Average and Running Trend Analysis (MARTA triangles), combined with a Pettitt's test change-point detection, highlighted a decreasing change of snow climatology occurring around the end of the 1980s. The comparison with winter temperature and precipitation data from the HISTALP dataset identified a major role played by temperature on the long-term decrease and changing points of snow depth and SWE with respect to precipitation, mainly responsible for its variability. Correlation with climatic indexes indicates significant negative values of the Pearson correlation coefficient with winter North Atlantic Oscillation (NAO) and positive values with winter Western Mediterranean Oscillation (WeMO) for some areas and elevation classes. Results of this climatology are synthesized in a temporal polynomial model that is useful for climatological studies and water resources management in mountain areas
A multi‐century meteo‐hydrological analysis in the Italian Alps: daily streamflow (1862–2022) at different time scales
Full text linkIn this paper, the second longest time series of daily hydrometric levels and streamflow for an Italian river, Adige, in the Italian Alps, also one of the longest worldwide and unpublished so far, is reconstructed and analyzed. Daily streamflow prior to 1923, when the official mean daily discharge was first published, is estimated based on daily water levels collected since January 1862, cross-section geometry, discharge, and surface velocity measurements at the hydrometric station of Trento. The main objective of this paper is the identification, attribution, and quantification of the impact of natural and anthropic factors on changes in streamflow in a mountain region with marked orographic and climatic gradients. The resulting 161-year-long time series, until December 2022, for this 9763 km2 catchment is firstly analyzed in search of trends and their statistical significance, spectral properties at different time scales and periods, changes in the monthly regime prior to and after the constructions of reservoirs. The observed −1.0 mm year−1 slope of the annual streamflow linear trendline is statistically significant and indicates a decline of −1.4% per decade of available streamflow in the river, similar to the one observed in nearby basins. The spectral analysis conducted with the wavelet transform indicates that a sudden change of spectral properties and trends of daily streamflow occurred inside the pre- and post-reservoir construction period and can be explained also as a result of a more environment-oriented legislation. A wavelet coherence spectrum between streamflow and teleconnection indices indicates the existence of a significant coherence with the Atlantic Multidecadal Oscillation only. The comparison with estimated actual reference evapotranspiration losses and temperature points out that the observed temperature increase is not sufficient to explain the observed hydrological losses, being precipitation almost constant over the observation period. The observed increase of 86 mm of hydrological losses over the last century is explained in terms of water withdrawals for agricultural, civil, and industrial needs (38 mm), enhanced evapotranspiration due to temperature increase (30 mm), expanded artificial lakes' surface (1 mm), the residual of 17 mm being attributed to land-use changes with afforestatio
A Multi-Century Meteo-Hydrological Analysis in the Italian Alps: Daily Streamflow (1862–2022) at Different Time Scales
No full textIn this paper, the second longest time series of daily hydrometric levels and streamflow for an Italian river, Adige, in the Italian Alps, also one of the longest worldwide and unpublished so far, is reconstructed and analyzed. Daily streamflow prior to 1923, when the official mean daily discharge was first published, is estimated based on daily water levels collected since January 1862, cross-section geometry, discharge, and surface velocity measurements at the hydrometric station of Trento. The main objective of this paper is the identification, attribution, and quantification of the impact of natural and anthropic factors on changes in streamflow in a mountain region with marked orographic and climatic gradients. The resulting 161-year-long time series, until December 2022, for this 9763 km2 catchment is firstly analyzed in search of trends and their statistical significance, spectral properties at different time scales and periods, changes in the monthly regime prior to and after the constructions of reservoirs. The observed -1.0 mm year-1 slope of the annual streamflow linear trendline is statistically significant and indicates a decline of -1.4% per decade of available streamflow in the river, similar to the one observed in nearby basins. The spectral analysis conducted with the wavelet transform indicates that a sudden change of spectral properties and trends of daily streamflow occurred inside the pre- and post-reservoir construction period and can be explained also as a result of a more environment-oriented legislation. A wavelet coherence spectrum between streamflow and teleconnection indices indicates the existence of a significant coherence with the Atlantic Multidecadal Oscillation only. The comparison with estimated actual reference evapotranspiration losses and temperature points out that the observed temperature increase is not sufficient to explain the observed hydrological losses, being precipitation almost constant over the observation period. The observed increase of 86 mm of hydrological losses over the last century is explained in terms of water withdrawals for agricultural, civil, and industrial needs (38 mm), enhanced evapotranspiration due to temperature increase (30 mm), expanded artificial lakes' surface (1 mm), the residual of 17 mm being attributed to land-use changes with afforestation
Surface melting over the Greenland ice sheet derived from enhanced resolution passive microwave brightness temperatures (1979-2019)
Full text linkSurface melting is a major component of the Greenland ice sheet surface mass balance, and it affects sea level rise through direct runoff and the modulation of ice dynamics and hydrological processes, supraglacially, englacially and subglacially. Passive microwave (PMW) brightness temperature observations are of paramount importance in studying the spatial and temporal evolution of surface melting due to their long temporal coverage (1979-present) and high temporal resolution (daily). However, a major limitation of PMW datasets has been the relatively coarse spatial resolution, which has historically been of the order of tens of kilometers. Here, we use a newly released PMW dataset (37 GHz, horizontal polarization) made available through a NASA "Making Earth System Data Records for Use in Research Environments"(MeASUREs) program to study the spatiotemporal evolution of surface melting over the Greenland ice sheet at an enhanced spatial resolution of 3.125 km. We assess the outputs of different detection algorithms using data collected by automatic weather stations (AWSs) and the outputs of the Modèle Atmosphérique Régional (MAR) regional climate model. We found that sporadic melting is well captured using a dynamic algorithm based on the outputs of the Microwave Emission Model of Layered Snowpack (MEMLS), whereas a fixed threshold of 245 K is capable of detecting persistent melt. Our results indicate that, during the reference period from 1979 to 2019 (from 1988 to 2019), surface melting over the ice sheet increased in terms of both duration, up to 4.5 (2.9) d per decade, and extension, up to 6.9 % (3.6 %) of the entire ice sheet surface extent per decade, according to the MEMLS algorithm. Furthermore, the melting season started up to 4.0 (2.5) d earlier and ended 7.0 (3.9) d later per decade. We also explored the information content of the enhanced-resolution dataset with respect to the one at 25 km and MAR outputs using a semi-variogram approach. We found that the enhanced product is more sensitive to local-scale processes, thereby confirming the potential of this new enhanced product for monitoring surface melting over Greenland at a higher spatial resolution than the historical products and for monitoring its impact on sea level rise. This offers the opportunity to improve our understanding of the processes driving melting, to validate modeled melt extent at high resolution and, potentially, to assimilate these data in climate models
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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