1,721,028 research outputs found
Evaluation of the similarity between drought indices by correlation analysis and Cohen's Kappa test in a Mediterranean area
No full textIn the literature, numerous papers report comparative analyses of drought indices. In these types of studies, the similarity between drought indices is usually evaluated using the Pearson correlation coefficient, r, calculated between corresponding severity time series. However, it is well known that the correlation does not describe the strength of agreement between two variables. Two drought indices can exhibit a high degree of correlation but can, at the same time, disagree substantially, for example, if one index is consistently higher than the other. From an operational point of view, two indices can be considered in agreement when they indicate the same severity category for a given period (e.g. moderate drought). In this work, we compared six meteorological drought indices based on both correlation analysis and Cohen's Kappa test. This test is typically used in medical or social sciences to obtain a quantitative assessment of the degree of agreement between different methods or analysts. The indices considered are five timescale-dependent indices, i.e. the Percent of Normal Index, the Deciles Index, the Percentile Index, the Rainfall Anomaly Index, and the Standardised Precipitation Index, computed at the 1-, 3-, and 6-month timescales, and the Effective Drought Index, a relatively new index, which has a self-defined timescale. The indices were calculated for 15 stations in the Abruzzo region (central Italy) during 1951–2018. We found that the strength of agreement depends on both the criteria of drought severity classification and the different indices' calculation methods. The Cohen's Kappa test indicates a prevailing moderate or fair agreement among the indices considered, despite the generally very high correlation between the corresponding severity times series. The results demonstrate that the Cohen's Kappa test is more effective than the correlation analysis in discriminating the actual strength of agreement/disagreement between drought indices
Practical thresholds to distinguish erosive and rill rainfall events
No full textIn this paper, 1017 rainfall events from 2008 to 2017 are used to identify the rainfall threshold that produces upland erosion at the Masse (central Italy) and Sparacia (southern Italy) experimental stations. The rainfall events are classified into three classes: non-erosive, interrill-only and rill. The threshold values for separating as correctly as possible the erosive rains (case I) and the rill rains (case II) are derived solely from the hyetograph. Each threshold value is obtained by imposing that the long-term erosivity of the events above the threshold is equal to the long-term erosivity of all erosive events (case I) or only rill events (case II). The performances of selective criteria based on 31 threshold variables are compared, and those most effective in separating erosive and rill events are identified. The identification of the best criterion depends on the aim of the analysis. It could be required to provide the greatest accuracy for separating erosive and rill events or the lowest error in the prediction of long-term erosivity. In general, the results clearly show that the best variables are those that quantify the characteristics of rainfall patterns, such as rain showers (periods of continuous rain) and the deviations in the rain records over a truncation level. These results are especially significant for the operational estimation of rainfall erosivity and for identifying the trigger of the erosion process and rill development by using only a hyetograph. This is obtained by relatively simple field measurements and is also widely available on a global scale. The most effective variables are potentially usable in water erosion prediction models as proxies of variables that are more rarely available and/or more difficult to measure
Sviluppo e valutazione di pratiche soglie per separare le piogge erosive responsabili di processi interrill e rill
No full textFor the experimental station Masse threshold levels able to separate interrill erosive
events from non erosive events were developed and tested. The Masse database
was composed of 258 rainy events (189 non-erosive events and 70 interrill erosive
events). Thresholds for separating erosive-interrill events from erosive-rill events
were developed and verified at Sparacia analysing 77 erosive events (64 interrill and
13 rill). At Masse the threshold in terms of event rainfall depth, Pe, was, among the
analyzed variables, the most effective one to distinguish between non-erosive and
erosive interrill rainfall events. The rainfall events with a total depth Pe > 13 mm are
identified as interrill erosive events. This value is very similar to the 12.7 mm selected
by Wischmeier and Smith (1958) that propose a compound criterion (Pe > 12.7 mm or
I15 > 6,35 mm in 15 minutes). In our case the compound criterion does not guarantee an improvement in the effectiveness of the single threshold. At Sparacia the threshold I15 > 8,75 mm in 15 min is the most effective, among those analyzed, to select erosive
rill events from all erosive events
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
3D #DigitalInvasions: a crowdsourcing project for mobile user generated content
Full text linkThis paper introduces the #InvasioniDigitali project which is an online crowdsourcing initiative started in Italy in 2013 with the aim to promote the value of and engagement with local heritage. The paper focuses on two case studies of pilot ‘invasions’ using 3D data capture by students at museums and heritage sites in Sicily
Changes in soil hydrodynamic parameters during intermittent rainfall following tillage
Full text linkThe changes in the soil hydrodynamic properties following soil tillage were investigated in rainfall simulation trials of intermittent rain at the Masse experimental station (Soil Erosion LABoratory, SERLAB) in central Italy. The experiments were designed to build a database as representative as possible of situations that may occur in nature. The data collected during the experiments were used to determine the saturated soil hydraulic conductivity, Ks, the soil sorptivity at the antecedent soil–water matric potential Ψi, S, and the flow-weighted mean pore size at Ψi, λm. It was also verified if the energy content of total rainfall after tillage explained the short-term temporal variability of Ks. The results showed that during a sequence of rainfalls with wetting and drying cycles, there was a reduction of both S and Ks by 2.9–3.1 and 1.4–2.2 times, respectively, depending on the plot. This decrease was abrupt for S and more gradual for Ks. The analysis confirmed that Ks decreased as the overall energy dissipated at the soil surface, E, increased. The range of possible Ks values should be expected to become smaller as the dissipated rainfall energy after tillage increases (<30 mm/h for E = 2 kJ/m2 and < 5 mm/h for E = 8 kJ/m2). For this reason, for the prediction and mathematical simulation of the rainfall-runoff transformation process, it is not advisable to limit the investigation to a single hydraulic characterization carried out immediately or shortly after tillage but data should be collected in a relatively long time span after tillage to properly characterize the soil in a condition favourable to surface runoff occurrence. For very high energy values, a recovery mechanism of the hydraulic properties of the altered/compacted layer was observed, but this behaviour should be confirmed by further investigations
- …
