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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
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
Setup and calibration of the rainfall simulator of the Masse experimental station for soil erosion studies
No full textThis note describes the technical characteristics and the preliminary setup and calibration of a nozzle-type rainfall simulator installed at the University of Perugia's Masse experimental station. This simulator includes some innovative features, usually not present in similar low-cost instruments employed in field experiments: 1) both single and multi-nozzle operation are feasible, thus enabling the possibility to simulate variable-intensity rainfall events; 2) events are simultaneously reproduced in two identical plots (width 1 m, length 0.92 m, and slope 16%), thus obtaining two replications for each experiment; 3) the runoff volume coming from the micro-plots and the water volume falling outside the plots are both collected and conveyed to separate outlets, thus allowing an easy calculation of the infiltrated volumes and of the system efficiency. The first step of the calibration regarded the spatial distribution of rainfall, the stability of the rainfall intensity over time (within the experiment), and the reproducibility of the rainfall intensities both in space (between the two plots) and over time (among successive experiments). Next, the drop size distribution (DSD) and the related rainfall characteristics (median volumetric drop diameter D50 and mean kinetic energy per unit area and unit depth) were evaluated by the oil method for the single and some multi-nozzle applications. An effective automatic drop recognition procedure by the Fiji open-source software is proposed and illustrated. Results indicate a high uniformity of rainfall (Christiansen uniformity coefficient > 92%) in both single and multi-nozzle operation for both plots. The reproducibility of experiments over short time intervals and under similar environmental conditions is satisfactory (coefficient of variation of mean intensity < 3%). Comparing initial and final rainfall intensity values, a slight decrease was observed within each experiment (about 2% on average). Some systematic differences in rainfall intensity were also detected between the plots. The analysis of both the intensity and the DSD in the multi-nozzle operation indicated the presence of some interference among the individual sprays when larger nozzles are simultaneously activated. Moreover, in agreement with the literature, it was confirmed that this type of rainfall simulator always produces kinetic energy values lower than those associated with natural rainfall of similar intensit
A Check of Water Drop Impact Effects on Surface Soil Saturated Hydraulic Conductivity
No full textThe post-tillage dynamics of the surface soil saturated hydraulic conductivity, Ks, was studied at the Masse experimental station (central Italy, silty-clay-loam soil). A sequence of experiments was performed by rainfall simulation on two replicated micro-plots (width 1 m, length 0.92 m, slope 16%) established on bare soil. Each high-intensity rainfall simulation was preceded by a low-intensity wetting phase. The soil water content, w, was measured before wetting and both before and after simulation. Runoff was measured at 5 min intervals. The infiltration rate was calculated as the difference between rainfall intensity and runoff rate. Finally, Ks was assumed to be equal to the infiltration rate under the nearly steady conditions reached at the end of each simulation. The pre-wetting w values were quite low and they increased during wetting, reaching at the end of this phase a value that remained more or less stable during the simulation phase. Consequently, all changes of Ks were expected to be specifically attributable to mechanical modifications of the porous medium due to the raindrop impact. For each individual experiment, Ks decreased with cumulative rainfall energy, E, according to an exponential or power relationship, denoting that raindrop impact had a noticeable effect on Ks when it occurred on an initially tilled soil. The developed experimental methodology appears usable to determine raindrop impact effects on the surface soil Ks in highly controlled field conditions and it could be applied to develop Ks versus E relationships usable for numerically simulating surface soil hydrological processes
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
Comparing Sentinel-1, Sentinel-2, and Landsat-8 data in the early recognition of irrigated areas in central Italy
No full textThis study evaluated the effectiveness of various remote sensing (RS) data (Sentinel-1, Sentinel-2, and Landsat 8) in the early recognition of irrigated areas in a densely cultivated area of central Italy. The study was based on crop data collected on more than 2000 plots in 2016 and 2017, characterized by quite different climatic conditions. The different RS data sources were used both alone and combined and with precipitation to define corresponding random forest (RF) classifiers whose overall accuracy (OA) was assessed by gradually increasing the number of available features from the beginning of the irrigation season. All tested RF classifiers reach stable OAs (OA 0.9) after 7-8 weeks from the start of the irrigation season. The performance of the radar indexes slightly improves when used in combination with precipitation data, but three weeks of features are required to obtain OA above 80%. The optical indices alone (Sentinel-2 and Landsat 8) reach OA ≈85% in the first week of observation. However, they are ineffective in cloudy conditions or when rainfed and irrigated fields have similar vigour. The most effective and robust indices are those based on combined sources (radar, optical, and meteorological), allowing OAs of about 92% and 96% at the beginning and in the middle of the irrigation season, respectively
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
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