ED Threshold Research Articles

Landslide rainfall threshold for landslide warning in Northern Thailand

Northern Thailand is a hotspot for landslides. Rainfall-triggered landslides in this region have caused much suffering and many fatalities. In this work, a landslide-triggering rainfall threshold for Northern Thailand is proposed based on rainfall data relating to 48 triggering rainfall events that caused 59 landslides in the study area. To account for different mechanism of landslide formation, the threshold was portioned into two parts for different duration of rainfall events. A split point of 3 days was chosen as a separator for portioning the threshold to be 1) a threshold for rainfall events of duration no longer than 3 days and 2) a threshold for rainfall events of duration longer than 3 days. The threshold also required a suitable variable for antecedent rainfalls which was found to be cumulative rainfall over 25-day period (CR 25) of 140 mm. Therefore, the thresholds combining cumulative rainfall with rainfall event - duration (CED) were established by incorporating the CR25 of 140 mm into the traditional ED threshold. This is the first attempt to incorporate the difference mechanism of landslide formation by dividing the CED threshold to two portions for difference rainfall duration. The introduced threshold shows positive sign of the prediction, particularly in term of false alarm rate, false alarm ratio, and critical success index. The introduced threshold will be useful for landslide warning system in the study area.

The optimal rainfall thresholds and probabilistic rainfall conditions for a landslide early warning system for Chuncheon, Republic of Korea

The purpose of this study is to establish the criteria for a landslide early warning system (LEWS). We accomplished this by deriving optimal thresholds for the cumulative event rainfall–duration (ED) and identifying the characteristics of the rainfall variables associated with a high probability of landslide occurrence via a Bayesian model. We have established these system criteria using rainfall and landslide data for Chuncheon, Republic of Korea. Heavy rainfall is the leading cause of landslides in Chuncheon; thus, it is crucial to determine the rainfall conditions that trigger landslides. Hourly rainfall data spanning 1999 to 2017 from seven gauging stations were utilized to establish the ED thresholds and the Bayesian model. We used three different calibration periods of rainfall events split by 12, 24, 48, and 96 non-rainfall hours to calibrate the ED thresholds. Finally, the optimal threshold was determined by comparing the results of the contingency table and the skill scores that maximize the probability of detection (POD) score and minimize the probability of false detection (POFD) score. In the LEWS, by considering the first level as “normal,” we developed subsequent step-by-step warning levels based on the Bayesian model as well as the ED thresholds. We propose the second level, “watch,” when the rainfall condition is above the ED thresholds. We then adopt the third level, “warning,” and the fourth level, “severe warning,” based on the probability of landslide occurrence determined via a Bayesian model that considers several factors including the rainfall conditions of landslide vs. non-landslide and various rainfall variables such as hourly maximum rainfall and 3-day antecedent rainfall conditions. The proposed alert level predicted a total of 98.2% of the landslide occurrences at the levels of “severe warning” and “warning” as a result of the model fitness verification. The false alarm rate is 0% for the severe warning level and 47.4% for the warning level. We propose using the optimal ED thresholds to forecast when landslides are likely to occur in the local region. Additionally, we propose the ranges of rainfall variables that represent a high landslide probability based on the Bayesian model to set the landslide warning standard that fits the local area’s characteristics.

Estimation of rainfall thresholds for shallow landslides in the Sierra Madre Oriental, northeastern Mexico

Landslides induced by prolonged rainfalls are frequent mass movements along the northeastern portion of the Sierra Madre Oriental in Mexico, causing significant damage to infrastructure. In this work, we have studied the connection between rainfall and landslides in the Santa Rosa Canyon, a catchment located in the northeastern Mexico. A landslide database triggered by major storms and hurricanes that have hit the region over the past 30 years was analyzed. A total of 92 rainfall events in the Santa Rosa Canyon were studied to determine the amount of precipitation needed to trigger shallow landslides. For each event the duration (D, in hours) and the cumulated rainfall event (E, in mm) were determined by using historical rainfall data from weather stations located near the study area. We have proposed an ED threshold for rainfall-induced landslides with durations 0.5 < D < 120 hours to address the conditions that trigger these events in the study area. On analyzing the obtained threshold, it has been established that almost 60 mm of a daily rainfall accumulation is required to trigger shallow landslides in the study area. This estimation is consistent with other calculations made for areas close to the Santa Rosa Canyon. Finally, we validated the predictive capability of the threshold with a different set of rainfall data that did not result in landslides performing a straightforward receiver operating characteristic analysis. A good approach was obtained, especially for rainfall events with daily measurements. Results could be used as input information in the design of a landslide early warning system for the northeastern Mexico, and replicated for other landslide prone areas in the region.

How much does the rainfall temporal resolution affect rainfall thresholds for landslide triggering?

In many areas of the world, the prediction of rainfall-induced landslides is usually carried out by means of empirical rainfall thresholds. Their definition is complicated by several issues, among which are the evaluation and quantification of diverse uncertainties resulting from data and methods. Threshold effectiveness and reliability strongly depend on the quality and quantity of rainfall measurements and landslide information used as input. In this work, the influence of the temporal resolution of rainfall measurements on the calculation of landslide-triggering rainfall thresholds is evaluated and discussed. For the purpose, hourly rainfall measurements collected by 172 rain gauges and geographical and temporal information on the occurrence of 561 rainfall-induced landslides in Liguria region (northern Italy) in the period 2004–2014 are used. To assess the impact of different temporal resolutions on the thresholds, rainfall measurements are clustered in increasing bins of 1, 3, 6, 12 and 24 h. A comprehensive tool is applied to each dataset to automatically reconstruct the rainfall conditions responsible for the failures and to calculate frequentist cumulated event rainfall–rainfall duration (ED) thresholds. Then, using a quantitative procedure, the calculated ED thresholds are validated. The main finding of the work is that the use of rainfall measurements with different temporal resolutions results in considerable variations of the shape and the validity range of the thresholds. Decreasing the rainfall temporal resolution, thresholds with smaller intercepts, higher slopes, shorter ranges of validity and higher uncertainties are obtained. On the other hand, it seems that the rainfall temporal resolution does not influence the validation procedure and the threshold performance indicators. Overall, the use of rainfall data with coarse temporal resolution causes a systematic underestimation of thresholds at short durations, resulting in relevant drawbacks (e.g. false alarms) if the thresholds are implemented in operational systems for landslide prediction.

Design of Multi-Carrier LBT for LAA&amp;WiFi Coexistence in Unlicensed Spectrum

To relieve the shortage problem of licensed spectrum, the aggregation of licensed and unlicensed carriers has emerged as an attractive solution for opportunistically increasing the throughput of LTE systems while enhancing the utilization of unlicensed spectrum. As one of the representative aggregation technologies, LAA is in favor of the harmonious coexistence with WiFi systems by leveraging the LBT mechanism and different pre-defined access priorities. In this article, we present a general overview of the attractive benefits and technical challenges for aggregating licensed carriers with unlicensed carriers. We then introduce some fundamental features of the LBT based LAA, including transmission modes, ED threshold, random backoff within the contention window, and access priority classes. Under multiple unlicensed channels, we propose two novel multi-carrier LBT mechanisms to improve the transmission behavior and coexistence performance of LAA and WiFi. It is verified in terms of successful transmission probability and carrier utilization rate that two proposed multi-carrier LBT mechanisms can achieve much better performance than the conventional counterpart using random carrier selection.

Calibration and validation of rainfall thresholds for shallow landslide forecasting in Sicily, southern Italy

Empirical rainfall thresholds are tools to forecast the possible occurrence of rainfall-induced shallow landslides. Accurate prediction of landslide occurrence requires reliable thresholds, which need to be properly validated before their use in operational warning systems. We exploited a catalogue of 200 rainfall conditions that have resulted in at least 223 shallow landslides in Sicily, southern Italy, in the 11-year period 2002–2011, to determine regional event duration–cumulated event rainfall (ED) thresholds for shallow landslide occurrence. We computed ED thresholds for different exceedance probability levels and determined the uncertainty associated to the thresholds using a consolidated bootstrap nonparametric technique. We further determined subregional thresholds, and we studied the role of lithology and seasonal periods in the initiation of shallow landslides in Sicily. Next, we validated the regional rainfall thresholds using 29 rainfall conditions that have resulted in 42 shallow landslides in Sicily in 2012. We based the validation on contingency tables, skill scores, and a receiver operating characteristic (ROC) analysis for thresholds at different exceedance probability levels, from 1% to 50%. Validation of rainfall thresholds is hampered by lack of information on landslide occurrence. Therefore, we considered the effects of variations in the contingencies and the skill scores caused by lack of information. Based on the results obtained, we propose a general methodology for the objective identification of a threshold that provides an optimal balance between maximization of correct predictions and minimization of incorrect predictions, including missed and false alarms. We expect that the methodology will increase the reliability of rainfall thresholds, fostering the operational use of validated rainfall thresholds in operational early warning system for regional shallow landslide forecasting.

Rainfall thresholds for shallow landslide occurrence in Calabria, southern Italy

Abstract. In many areas, rainfall is the primary trigger of landslides. Determining the rainfall conditions responsible for landslide occurrence is important, and may contribute to saving lives and properties. In a long-term national project for the definition of rainfall thresholds for possible landslide occurrence in Italy, we compiled a catalogue of 186 rainfall events that resulted in 251 shallow landslides in Calabria, southern Italy, from January 1996 to September 2011. Landslides were located geographically using Google Earth®, and were given a mapping and a temporal accuracy. We used the landslide information, and sub-hourly rainfall measurements obtained from two complementary networks of rain gauges, to determine cumulated event vs. rainfall duration (ED) thresholds for Calabria. For this purpose, we adopted an existing method used to prepare rainfall thresholds and to estimate their associated uncertainties in central Italy. The regional thresholds for Calabria were found to be nearly identical to previous ED thresholds for Calabria obtained using a reduced set of landslide information, and slightly higher than the ED thresholds obtained for central Italy. We segmented the regional catalogue of rainfall events with landslides in Calabria into lithology, soil regions, rainfall zones, and seasonal periods. The number of events in each subdivision was insufficient to determine reliable thresholds, but allowed for preliminary conclusions about the role of the environmental factors in the rainfall conditions responsible for shallow landslides in Calabria. We further segmented the regional catalogue based on administrative subdivisions used for hydro-meteorological monitoring and operational flood forecasting, and we determined separate ED thresholds for the Tyrrhenian and the Ionian coasts of Calabria. We expect the ED rainfall thresholds for Calabria to be used in regional and national landslide warning systems. The thresholds can also be used for landslide hazard and risk assessments, and for erosion and landscape evolution studies, in the study area and in similar physiographic regions in the Mediterranean area.

Lithological and seasonal control on rainfall thresholds for the possible initiation of landslides in central Italy

We compiled a catalogue of 442 rainfall events with landslides in the Abruzzo, Marche, and Umbria regions, central Italy, between February 2002 and August 2010. For each event, we determined the duration D (in hours) and the cumulated (total) event rainfall E (in mm), using rainfall measurements obtained from a dense network of 150 rain gauges. Landslides were mapped as single points using Google Earth®, and were attributed a level of mapping accuracy P, in four classes ( P 1 < 1 km 2, P 10 < 10 km 2, P 100 < 100 km 2, P 300 < 300 km 2). Using this information, we determined cumulated event rainfall–rainfall duration ( ED) thresholds, which are entirely equivalent to rainfall intensity–duration ( ID) thresholds, and avoid unnecessary conversions. To determine the ED thresholds, we modified a statistical method first proposed to determine ID thresholds. Adopting a bootstrapping statistical technique, we expanded the method to determine the uncertainty associated with the parameters that define the power law threshold model, and the sensitivity of the thresholds to the number of ( D, E) data points in the empirical data set. We determined ED thresholds for 1% and 5% exceedance probability levels: (i) for the entire study area, and for the three individual regions in the study area (Abruzzo, Marche, and Umbria); (ii) for three main lithological domains in the study area (post-orogenic sediments, flysch deposits, carbonate rocks); and (iii) for two seasonal periods (May–September, October–April). Comparison of the ED thresholds indicates that the cumulated amount of rainfall necessary to trigger landslides in flysch deposits is larger than in post-orogenic sediments and carbonate rocks. However, the ED thresholds for post-orogenic sediments and carbonate rocks were statistically indistinguishable in the study area. Also, the seasonal thresholds were statistically different for rainfall durations shorter than 12 h and longer than 100 h, but were indistinguishable in the range 12 < D < 100 h. The results obtained are directly applicable to landslide forecasting based on empirical rainfall thresholds, and have implications for landslide hazard and risk assessment, as well as for landslide erosion and landscape evolution studies, both in the study area and in the neighboring regions.

Comparison of reduced and standard light application in photodynamic therapy of the eye in two rabbit models

Current PDT treatment for age-related macular degeneration uses a standard radiant exposure of 50 J/cm(2) at an irradiance of 600 mW/cm(2). However; there is a general problem with the unusually high irradiance; in fact, the rate of photochemical production of singlet oxygen may be limited by insufficiently oxygenized neovascular tissue. It was the aim of this study to evaluate the efficacy of verteporfin (Visudyne) photoactivation to induce thrombosis of choriocapillaries and in experimentally induced corneal neovascularizations in rabbits by varying irradiance and retinal radiant exposure. The light-dose threshold to induce micro-thrombosis in the choriocapillaries (seven eyes) and in corneal neovascularizations (eight eyes) of Chinchilla-Bastard rabbits using different retinal irradiances (100 and 600 mW/cm(2)) at different radiant exposures (20, 10, 5, 2.5, 1.25, 0.62, and 0.3 J/cm(2)) was evaluated. Induction of neovascularizations was performed 7 days prior to PDT treatment using intracorneal silk sutures. A dose of 2 mg/kg verteporfin was intravenously infused 10 min before standard PDT. The criterion for vascular thrombosis was vessel closure as determined by fluorescein angiography 1 h and 1 day post exposure. Experiments on the choroid revealed vessel closure 1 h after irradiation at ED(50) = 10.8 J/cm(2) (both 600 and 100 mW/cm(2)) and after 24 h at ED(50) = 2.4 J/cm(2) (600 mW/cm(2)) versus 1.8 J/cm(2) (100 mW/cm(2)). Vessel closure was enhanced at irradiation with 100 mW/cm(2). Regarding corneal neovascularizations, vessel thrombosis was observable by dark appearance of irradiated clotted neovascular tissue and angiographically by a lack of leakage at ED(50) thresholds of 0.62 J/cm(2) (1 h) and 0.41 J/cm(2) (1 day) for 100 mW/cm(2) and of 0.99 J/cm(2) (1 h), and 0.67 J/cm(2) (1 day) for 600 mW/cm(2). Thus in both experiments thresholds for vessel closure were reduced by a factor of 1.5 for the lower intensity. Histology revealed more selective vessel occlusion without RPE and photoreceptor damage for 100 mW/cm(2) rather than 600 mW/cm(2) intensity at threshold irradiation. Low-intensity PDT with verteporfin for neovascular tissue seems to be more effective than regular high-intensity PDT. Future preclinical trials should address the issue of proper dosimetry for effective PDT in age-related macular degeneration.

Pump-probe detection of laser-induced microbubble formation in retinal pigment epithelium cells.

Microsecond laser pulses are currently being investigated in a new ophthalmic procedure for treatment of disorders associated with the retinal pigment epithelium (RPE). The precise mechanism for microsecond laser-induced RPE damage, however, has not been determined. We have previously shown that short pulse laser irradiation in the nanosecond to picosecond time domain causes transient microbubble formation around melanin granules in pigmented cells. Nanosecond time-resolved microscopy was previously used to visualize the intracellular cavitation dynamics. However, this technique is difficult to use with microsecond laser exposures, especially when multiple laser pulses are applied in a rapid sequence as in the clinical setting. Here we describe a simple pump-probe method for detecting transient light scattering signal from individual RPE cells when they are irradiated with nanosecond and microsecond laser pulses. For single 12 ns pulses the threshold for bubble detection was the same as the ED(50) threshold for cell death. For 6 micros pulse duration the threshold for bubble detection was about 10% higher than the threshold for cell death. With repetitive pulse trains at 500 Hz the ED(50) decreased about 25% for 10 and 100 pulses. Cells die when a single bubble was detected in a multiple pulse sequence.