集合预报的现状和前景

综合论述了近年来已在国际上引起高度重视的新一代动力随机预报方法 ——— 集合预报。 随着计算机技术的迅猛发展和由于大气初值和数值模式中物理过程存在着不确定性的事实, 这一方法无疑代表了数值天气预报未来演变发展的方向。 未来的天气预报产品预计将从“决定论”的预报转变为“随机论”的预报来正确地表达气象科学中这一所谓“可预报性问题”, 以便更好地为用户服务。 文中扼要地叙述了集合预报的概念、基本问题及其最新的研究动态和发展, 包括(1)如何建立和评估一个集合预报系统;(2)如何正确地表征大气初值和模式物理过程的不确定性与随机性;(3)如何从集合预报中提炼有用的预报信息和合理地解释、检验集合预报的产品, 特别是概率预报。 除了直接在天气预报上的应用, 还提到集合预报在气象观测和资料同化方面应用的动态, 以引起有关研究人员的注意。     

The use of the automatic inclinometric system for landslide early warning: the case of Cabella Ligure (North-Western Italy)

Following the flood events occurred in the 1993 autumn, a landslide affecting the village of Montaldo di Cosola was reactivated. Montaldo di Cosola is a small village located in North-Western Italy, on the Appennines Mountains. Historical data report of at least another similar episode occurred about one century ago.The landslide takes place over debris deposits, which are about 20–35 m deep, produced by an ancient landslide event. Underneath these debris deposits there is an altered layer of the calcareous-marly substratum of the Antola formation. The landslide, almost certainly triggered by the incision of the torrent Rio Montaldo, has a probable rotational geometry and takes place through slow and progressive continuous movements. The landslide typology impedes a precise dimensional definition. Only the order of magnitude of the main scarp width, which is of hundreds of meters, and the order of magnitude of the landslide volume, which is of some hundreds of thousands of cubic meters, can be indicated.A complex monitoring network has been installed in the area. This network includes an automatic inclinometric system (AIS) that automatically performs measurements, twice a day, along the entire length of a pipe that is 45 m deep. Measurements are taken every 50 cm and are then broadcasted to a remote station located in Torino.After the exceptional meteorological events occurred in October 2000, the AIS measured significant movements that have not yet stopped. On the basis of these available data it has been possible to locate the sliding surface at a depth of about 13 m at the level of a sandy–silty layer with some clay lenses inside. The movements measurements performed so far reveal a good correlation with the rainfalls. In particular it has been possible to identify a time lag of about 8–9 days between the occurrence of a rainfall peak and the corresponding peak in the recorded movements that were produced by these rainfalls.     

PSHA: is it science?

Probabilistic seismic hazard analysis (PSHA) is beginning to be seen as unreliable. The problem with PSHA is that its data are inadequate and its logic is defective. Much more reliable, and more scientific, are deterministic procedures, especially when coupled with engineering judgment.     

论滑坡地质模型

在综合性滑坡分类体系基础上,把握滑坡活动各要素的地位与作用,遴选最能表征其活动特点的主要因素,作为建模的基本要素,形成滑坡基本地质模型体系;随着勘探阶段的不同,针对不同的应用目的,建立滑坡具体地质模型体系。滑坡地质模型的建立可为其分析、计算、评价与监测预报奠定模式基础,并有助于对滑坡活动的全面抽象掌握,最终提高滑坡工作的科学系统性和实用性。     

Hydrologic conditions responsible for triggering the Sto e landslide, Slovenia

In two events, on November 15 and 17, 2000, near the Mangart Mountain (2679 m a.s.l.), NW Slovenia, two translational landslides (debris flow slides) with a total volume of more than 1.5 million m³ occurred on the Sto e slope composed of morainic material filled with silt fraction. The first landslide was associated with a dry and the second landslide with a wet debris-flow, respectively. The rain gauging station in the village of Log pod Mangartom recorded 1638.4 mm of rainfall (more than 60% of the average annual precipitation) in the 48 days before the events (rainfall intensity of 1.42 mm/h in 1152 h). The recorded rainfall depth has a recurrence interval of more than 100 years. Other recorded rainfall depths of shorter duration (481.6 mm in 7 days, 174.0 mm in 24 h, 70 mm in 1 h) have recurrence intervals of much less than 100 years. A hydrological analysis of the event showed that the increase in runoff coefficients during the wet period in autumn 2000 before the landslide was as high as two- to threefold. An analysis using natural isotopes of δ¹⁸O and tritium of water samples from the Sto e landslide area has shown permanent but slow exfiltration of underground waters from a reservoir in the slope. In the case of low-intensity and long-duration rainfall in autumn 2000, relatively low permeable (10⁻⁷ m/s) morainic material was nearly saturated but remained stable (average porosity 21%, water content 20%, liquid limit 25%) until high artesian pressures up to 100 m developed in the slope by slow exfiltration from the relatively high permeable (10⁻⁵ m/s) massive dolomite. The Sto e landslide (two debris flow slides) was triggered by high artesian pressures built in the slope after long-duration rainfall. The devastating debris-flows formed from the landslide masses by infiltration of rainfall and surface runoff into the landslide masses and by their liquefaction.     

Survey and monitoring of landslide displacements by means of L-band satellite SAR interferometry

This paper illustrates the capabilities of L-band satellite SAR interferometry for the investigation of landslide displacements. SAR data acquired by the L-band JERS satellite over the Italian and Swiss Alps have been analyzed together with C-band ERS-1/2 SAR data and in situ information. The use of L-band SAR data with a wavelength larger than the usual C-band, generally considered for ground motion measurements, reduces some of the limitations of differential SAR interferometry, in particular, signal decorrelation induced by vegetation cover and rapid displacements. The sites of the Alta Val Badia region in South Tyrol (Italy), Ruinon in Lombardia (Italy), Saas Grund in Valais (Switzerland) and Campo Vallemaggia in Ticino (Switzerland), representing a comprehensive set of different mass wasting phenomena in various environments, are considered. The landslides in the Alta Val Badia region are good examples for presenting the improved performance of L-band in comparison to C-band for vegetated areas, in particular concerning open forest. The landslides of Ruinon, Saas Grund, and Campo Vallemaggia demonstrate the strength of L-band in observing moderately fast displacements in comparison to C-band. This work, performed with historical SAR data from a satellite which operated until 1998, demonstrates the capabilities of future planned L-band SAR missions, like ALOS and TerraSAR-L, for landslide studies.     

Analysis of time-varying rainfall infiltration induced landslide

A case study of rainstorm-induced landslide is modeled following the hourly rainfall time series from the stage of infiltration caused by induced slope movement and soil saturated to excess pore pressures—Transient Rainfall Infiltration and Grid-based Regional Slope-Stability Analysis (TRIGRS). The grid-based landslide stability analysis was conducted to model the increased pore pressures and runoff in the study area under the specified rainfall conditions. The generated time variances of pore pressures help determine landslide characteristics and mechanisms under rainfall conditions. Inputs of soil properties and permeability parameters for landslide stability analysis in the study area were prepared by TRIGRS adopted for transient infiltration analysis. Results of the analyses show that under heavy rainfall conditions, the infiltrated slope is unstable and the time of debris masses movement initiated is correlated to the recorded time. In the initiated landslide, characteristics and effects are considered and reflected in the numerical modeling under combinations of topography, land use, climatic and geological conditions. Results reveal that there is a plane failure surface and a potential circular failure surface at the study site besides the rock topple failures in the crest. A grid-based slope-stability analysis incorporated with the GIS spatial functions is more advantageous than the traditional two-dimensional analysis for specified slope profiles to determine the whole behavior of a slope.     

Probabilistic landslide susceptibility and factor effect analysis

The susceptibility of landslides and the effect of landslide-related factors at Penang in Malaysia using the geographic information system (GIS) and remote sensing data have been evaluated. Landslide locations were identified in the study area from interpretation of aerial photographs and from field surveys. Topographical and geological data and satellite images were collected, processed, and constructed into a spatial database using GIS and image processing. The factors chosen that influence landslide occurrence were: topographic slope, topographic aspect, topographic curvature and distance from drainage, all from the topographic database; lithology and distance from lineament, taken from the geologic database; land use from Landsat Thermatic Mapper (TM) satellite images; and the vegetation index value from SPOT HRV (High-Resolution Visible) satellite images. Landslide hazardous areas were analyzed and mapped using the landslide-occurrence factors employing the probability–frequency ratio method using the all factors. To assess the effect of these factors, each factor was excluded from the analysis, and its effect verified using the landslide location data. As a result, all factors had relatively positive effects, except lithology, on the landslide susceptibility maps in the study area.     

Basic theory of three-dimensional landslide modeling based on the logical model of geologic structure

Dynamic visualization of landslide cross-sections is important for understanding the structure and mechanism of landslide formation. Moreover, the modeling of geologic information plays an effective role in geo-hazard assessment and their mitigation. In this study, we developed the basic theory of a three-dimensional landslide modeling and applied it to the Nigawa landslide of the Hyogo Prefecture in central Japan. The construction of this model is based on the boundary surfaces of slump blocks and geologic units, and the hierarchical relationships between these surfaces. An application algorithm was validated and the model proved efficient in depicting the nature of landslides in the Nigawa area.     

Systematic GIS-based landslide inventory as the first step for effective landslide-hazard management

The purpose of the so-called IFFI project (Inventario dei Fenomeni Franosi in Italia—Inventory of Landslides in Italy) and of many other related activities carried out by the Centro Regionale per le Ricerche Territoriali e Geologiche of ARPA Piemonte (Agenzia Regionale per la Protezione Ambientale—Regional Agency for Environmental Protection), is to map all the existing landslides in Piemonte (including both results of monitoring data and available historical data). ARPA carried out new systematic surveys using airphoto interpretation and created a specific alphanumeric geological information systems (GIS)-based database to store and process all the collected data. In order to obtain proper landslide-hazard zoning, it is necessary to provide a landslide inventory and to define the relationship between landslides and geological setting. A landslide inventory represents a fundamental base of knowledge, is a very basic tool for land planning, and strongly helps the local authorities in their decision making.