The risk management of rainfall-induced landslides requires reliable rainfall thresholds to issue early warning alerts. The practical application of these thresholds often leads to misclassifications, either false negative or false positive, which induce costs for the society. Since missed-alarm (false negative) and false-alarm (false positive) cost may be significantly different, it is necessary to find an optimal threshold that accounts for and minimises such costs, tuning the false-alarm and missed-alarm rates. In this paper, we propose a new methodology to develop cost-sensitive rainfall thresholds, and we also analyse several factors that produce uncertainty, such as the accuracy of rainfall intensity values at landslide location, the time of occurrence, the minimum rainfall amount to define the non-triggering event, and the variability of cost scenarios. Starting from a detailed mapping of landslides that occurred during five large-scale rainfall events in the Italian Central Alps, we first developed rainfall threshold curves with a ROC-based approach by using both rain gauge and bias-adjusted weather radar data. Then, based on a reference cost scenario in which we quantified several cost items for both missed alarms and false alarms, we developed cost-sensitive rainfall threshold curves by using cost-curve approach (Drummond and Holte 2000). Finally, we studied the sensitivity of cost items. The study confirms how important is the information regarding rainfall intensity at the landslide site for the development of rainfall thresholds. Although the use of bias-corrected radar strongly improves these values, a large uncertainty related to the exact time of landslide occurrence still remains, negatively affecting the analysis. Accounting for the different missed-alarm and false-alarm misclassification costs is important because different combinations of these costs make an increase or decrease of the rainfall thresholds convenient. In our reference cost scenario, the most convenient threshold is lower than ROC-based thresholds because it seeks to minimise the number of missed alarms, whereas the missed-alarm costs are almost seven times greater than false-alarm costs. However, for different cost scenarios, threshold may vary significantly, as much as half an order of magnitude.
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Alexander Wittig Camilla Colombo Roberto Armellin 《Celestial Mechanics and Dynamical Astronomy》2017,128(4):435-452
This paper introduces and combines for the first time two techniques to allow long-term density propagation in astrodynamics. First, we introduce an efficient method for the propagation of phase space densities based on differential algebra (DA) techniques. Second, this DA density propagator is used in combination with a DA implementation of the averaged orbital dynamics through semi-analytical methods. This approach combines the power of orbit averaging with the efficiency of DA techniques. While the DA-based method for the propagation of densities introduced in this paper is independent of the dynamical system under consideration, the particular combination of DA techniques with averaged equations of motion yields a fast and accurate technique to propagate large clouds of initial conditions and their associated probability density functions very efficiently for long time. This enables the study of the long-term behavior of particles subjected to the given dynamics. To demonstrate the effectiveness of the proposed approach, the evolution of a cloud of high area-to-mass objects in Medium Earth Orbit is reproduced considering the effects of solar radiation pressure, the Earth’s oblateness and luni-solar perturbations. The method can propagate 10,000 random fragments and their density for 1 year within a few seconds on a common desktop PC. 相似文献
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A Holocene lake sediment record is presented from Lake N14 situated on Angissoq Island 15 km off the main coast of southern Greenland. The palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica, clastic material, organic material and sulphur as well as sedimentation rate, moss content and magnetic susceptibility. A total of 43 radiocarbon dates has ensured a reliable chronology. It is argued that varying sediment composition mainly reflects changing precipitation. By analogy with the present meteorological conditions in southern Greenland, Holocene climate development is inferred. Between 11 550 and 9300 cal. yr BP temperature and precipitation increase markedly, but this period is climatically unstable. From 9300 yr BP conditions become more stable and a Holocene climatic optimum, characterised by warm and humid conditions, is observed from 8000 to 5000 cal. yr BP. From 4700 cal. yr BP the first signs of a climatic deterioration are observed, and from 3700 cal. yr BP the climate has become more dry and cold. Superimposed on the climatic long‐term trend is climate variability on a centennial time‐scale that increases in amplitude after 3700 cal. yr BP. A climatic scenario related to the strength and position of the Greenland high‐pressure cell and the Iceland low‐pressure cell is proposed to explain the Holocene centennial climate variability. A comparison of the Lake N14 record with a terrestrial as well as a marine record from the eastern North Atlantic Ocean suggests that the centennial climate variability was uniform over large areas at certain times. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Camilla Colombo Massimiliano Vasile Gianmarco Radice 《Celestial Mechanics and Dynamical Astronomy》2009,105(1-3):75-112
In this paper an optimisation algorithm based on Differential dynamic programming is applied to the design of rendezvous and fly-by trajectories to near Earth objects. Differential dynamic programming is a successive approximation technique that computes a feedback control law in correspondence of a fixed number of decision times. In this way the high dimensional problem characteristic of low-thrust optimisation is reduced into a series of small dimensional problems. The proposed method exploits the stage-wise approach to incorporate an adaptive refinement of the discretisation mesh within the optimisation process. A particular interpolation technique was used to preserve the feedback nature of the control law, thus improving robustness against some approximation errors introduced during the adaptation process. The algorithm implements global variations of the control law, which ensure a further increase in robustness. The results presented show how the proposed approach is capable of fully exploiting the multi-body dynamics of the problem; in fact, in one of the study cases, a fly-by of the Earth is scheduled, which was not included in the first guess solution. 相似文献
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C.I. Mathison 《Lithos》1975,8(2):93-111
16 chemical analyses and 71 microprobe analyses of magnetites and ilmenitesin the Somerset Dam layered basic intrusion demonstrate that the chemistry of these oxides is a sensitive indicator of crystallisation and subsolidus conditions. Microprobe analyses prove the existence of two chemically distinct types of ilmenite — secondary ilmenite formed by subsolidus oxidation of magnetite-ulvöspinelss, and primary ilmenite, which has been only partially affected by the subsolidus oxidation.Application of experimental TfOaX relations shows that the inferred crystallisation conditions approximately the NNO buffer. Subsolidus cooling appears to have occurred approximately parallel to the NNO buffer, and was probably buffered partly an H2O-rich fluid, and partly by the Fe-Ti oxides. The proportions of H2O and of sulphur compounds appear to have determined the temperatures at which subsolidus oxidation of magnetite ceased. 相似文献
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Sala Gianluca Lanfranconi Camilla Frattini Paolo Rusconi Giulia Crosta Giovanni B. 《Landslides》2021,18(9):2979-2992
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Based on Norwegian and Swedish representative national samples, and samples from areas with large mammalian carnivores present, we investigated whether well-known predictors for approval of wolves may explain between-country differences. Swedes were in general more positive than Norwegians were, while respondents in large carnivore areas, regardless of nationality, were less positive. The profile of those who approved wolf presence was the same in all samples. The difference between the samples was greater in Sweden, indicating that the relationship between urbanized and rural areas is more polarized in Sweden compared to Norway. We suggest this to be an effect of the fact that Norway’s large carnivore and agriculture policies favor the rural population, and of a higher degree of urbanization in Sweden. We recommend future studies to look into the different power relations between people living in urban and rural areas, comparing countries with different degree of urbanization. 相似文献
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