Statistical and spatial analysis of landslide susceptibility maps with different classification systems

The final publication is available at Springer via http://dx.doi.org/10.1007/s12665-016-6124-1A landslide susceptibility map is an essential tool for land-use spatial planning and management in mountain areas. However, a classification system used for readability determines the final appearance of the map and may therefore influence the decision-making tasks adopted. The present paper addresses the spatial comparison and the accuracy assessment of some well-known classification methods applied to a susceptibility map that was based on a discriminant statistical model in an area in the Eastern Pyrenees. A number of statistical approaches (Spearman’s correlation, kappa index, factorial and cluster analyses and landslide density index) for map comparison were performed to quantify the information provided by the usual image analysis. The results showed the reliability and consistency of the kappa index against Spearman’s correlation as accuracy measures to assess the spatial agreement between maps. Inferential tests between unweighted and linear weighted kappa results showed that all the maps were more reliable in classifying areas of highest susceptibility and less reliable in classifying areas of low to moderate susceptibility. The spatial variability detected and quantified by factorial and cluster analyses showed that the maps classified by quantile and natural break methods were the closest whereas those classified by landslide percentage and equal interval methods displayed the greatest differences. The difference image analysis showed that the five classified maps only matched 9 % of the area. This area corresponded to the steeper slopes and the steeper watershed angle with forestless and sunny slopes at low altitudes. This means that the five maps coincide in identifying and classifying the most dangerous areas. The equal interval map overestimated the susceptibility of the study area, and the landslide percentage map was considered to be a very optimistic model. The spatial pattern of the quantile and natural break maps was very similar, but the latter was more consistent and predicted potential landslides more efficiently and reliably in the study area.Peer ReviewedPreprin

Evaluación del riesgo sísmico mediante métodos avanzados y técnicas GIS. Aplicación a la ciudad de Barcelona.

Este trabajo es una contribución al desarrollo y aplicación de métodos avanzados de análisis de riesgo sísmico en grandes ciudades y se ha estructurado en dos partes: la primera establece el marco teórico de los estudios de riesgo sísmico, detallando los modelos y desarrollos avanzados para la evaluación del daño físico sobre edificios residenciales y de su impacto sobre la población, así como otros aspectos con él relacionados; la segunda describe la aplicación a Barcelona. Se usan dos métodos que se aplican a dos escenarios. El primer método, al que nos referimos como Método del Índice de vulnerabilidad (MIV), considera cinco estados de daño no nulo, define la acción en términos de intensidad macrosísmica y el edificio mediante un índice de vulnerabilidad; el grado de daño esperado se efectúa mediante funciones semiempíricas que dependen de la intensidad y del índice de vulnerabilidad. El segundo método, al que nos referimos como Método del Espectro de Capacidad (MEC) considera cuatro estados de daño no nulo, define la acción sísmica en términos de espectros de respuesta, y el edificio por medio de su espectro de capacidad. El grado de daño esperado se obtiene mediante el desarrollo de curvas de fragilidad y matrices de probabilidad de daño. Para la aplicación de ambos métodos a Barcelona se usa un escenario determinista y uno probabilista. Otra de las aportaciones relevantes de esta investigación es la creación de una herramienta, potente y versátil, diseñada sobre un Sistema de Información Geográfica (SIG) o Geographic Information System (GIS). Esta aplicación permite la integración, explotación y gestión de los datos. Este tipo de programas es imprescindible para cartografiar escenarios georreferenciados y va más allá de la aplicación concreta, pues su actualización es rápida y es de fácil adaptación para estudios de otros riesgos en la misma ciudad o en otras ciudades.Los resultados obtenidos son consistentes con la evolución histórica de la ciudad y con su condición actual, así como con las características de los suelos, poniendo de manifiesto la robustez de los métodos empleados. En general se observa una estructura radial del daño esperado con un mayor daño en Ciutat Vella y menor daño en los distritos periféricos. Destaca también el daño esperado en los pequeños núcleos de los pueblos antiguos de los actuales distritos. El MIV representa mejor las peculiaridades de los edificios individuales. El MEC suaviza estas características clasificando los edificios en 6 clases. El escenario más favorable es el determinista cuando se analiza mediante el MEC con daños esperados entre nulo, leve y moderado; el grado de daño medio de la ciudad es leve. Los más desfavorables son el determinista y probabilista cuando se analizan con el MIV; en ambos casos el estado de daño medio global es moderado. El distrito de l'Eixample destaca por ser el de mayor riesgo debido a la vulnerabilidad de sus edificios, a la alta densidad de edificios y población y al valor expuesto. Se confirma que, en ciudades como Barcelona, situadas en regiones de peligro sísmico entre bajo y moderado, la escasa o nula conciencia del peligro sísmico y la ausencia de precauciones de protección sísmica conduce a una elevada vulnerabilidad de sus edificios y, consecuentemente, a un elevado riesgo. En efecto, para escenarios relativamente moderados, con intensidades entre VI y VII, se esperan daños considerables. Los daños a la población son relevantes y su evaluación es muy sensible a los modelos de víctimas. En este sentido es preciso considerar los valores numéricos concretos como pronósticos del orden de magnitud de las cantidades evaluadas, y, en cualquier caso, se deben interpretar, desde una óptica probabilista, como valores medios para escenarios sísmicos creíbles.Los resultados de este estudio son de una enorme utilidad para la prevención y minoración del riesgo sísmico y para la planificación y gestión de emergencias

Seismic damage evaluation in urban areas using the capacity spectrum method: Application to Barcelona

Conceptual aspects related to seismic vulnerability, damage and risk evaluation are discussed first, together with a short review of the most widely used possibilities for seismic evaluation of structures. The capacity spectrum method and the way of obtaining seismic damage scenarios for urban areas starting from capacity and fragility curves are then discussed. The determination of capacity curves for buildings using non-linear structural analysis tools is then explained, together with a simplified expeditious procedure allowing the development of fragility curves. The seismic risk of the buildings of Barcelona, Spain, is analyzed in the paper, based on the application of the capacity spectrum method. The seismic hazard in the area of the city is described by means of the reduced 5% damped elastic response spectrum. The information on the buildings was obtained by collecting, arranging, improving and completing a broad database of the dwellings and current buildings. The buildings existing in Barcelona are mainly of two types: unreinforced masonry structures and reinforced concrete buildings with waffled-slab floors. The ArcView software was used to create a GIS tool for managing the collected information in order to develop seismic risk scenarios. This study shows that the vulnerability of the buildings is significant in Barcelona and, therefore, in spite of the low-to-moderate seismic hazard in the region, the expected seismic risk is considerable

Evaluation of social context integrated into the study of seismic risk for urban areas

Usually the seismic risk evaluation involves only the estimation of the expected physical damage, casualties or economic losses. This article corresponds to a holistic approach for seismic risk assessment which involves the evaluation of the social fragility and the lack of resilience. The complementary evaluation of social context aspects such as the distribution of the population, the absence of economic and social development, deficiencies in institutional management, and lack of capacity for response and recovery; is useful in order to have seismic risk evaluation suitable to support a decision making processes for risk reduction. The proposed methodology allows a standardized assessment of the social fragility and lack of resilience, by means of an aggravating coefficient of which summarizes the characteristics of the social context using fuzzy sets and Analytic Hierarchy Process (AHP). The selection of 20 social indicators is based on the indicators used by urban observatories of United Nations and other social researchers. These indicators are classified according to social item they describe, in six categories. Applying the determination level analysis, thirteen prevailing social indicators are selected. The proposed methodology has been applied in the cities of Merida (Venezuela) and Barcelona (Spain

Evaluation of social context integrated into the study of seismic risk for urban areas

Usually the seismic risk evaluation involves only the estimation of the expected physical damage, casualties or economic losses. This article corresponds to a holistic approach for seismic risk assessment which involves the evaluation of the social fragility and the lack of resilience. The complementary evaluation of social context aspects such as the distribution of the population, the absence of economic and social development, deficiencies in institutional management, and lack of capacity for response and recovery; is useful in order to have seismic risk evaluation suitable to support a decision making processes for risk reduction. The proposed methodology allows a standardized assessment of the social fragility and lack of resilience, by means of an aggravating coefficient of which summarizes the characteristics of the social context using fuzzy sets and Analytic Hierarchy Process (AHP). The selection of 20 social indicators is based on the indicators used by urban observatories of United Nations and other social researchers. These indicators are classified according to social item they describe, in six categories. Applying the determination level analysis, thirteen prevailing social indicators are selected. The proposed methodology has been applied in the cities of Merida (Venezuela) and Barcelona (Spain).Peer ReviewedPostprint (published version

Effect of rockfall fragmentation on exposure and subsequent risk analysis

Rockfalls are frequent natural processes in mountain regions with the potential to produce damage. The quantitative risk analysis (QRA) is an approach increasingly used to assess risk and evaluate the performance of mitigation measures. In case of the fragmentation of the falling rock mass, some of the hypothesis taken in the QRA estimation for rockfalls have to be modified since a single block or rock mass can produce several fragments thus modifying the runout probability, the impact energies and exposure of the elements at risk. In this contribution, we present a procedure to account for the exposure in QRA analysis along linear paths using the fragmental rockfall propagation model RockGIS (Matas et al. 2017). The procedure is applied at the “Monasterio de Piedra”, Spain as part of a QRA.Postprint (published version

Disaster risk reduction: a decision-making support tool based on the morphological analysis

Risk management due to natural hazards is a multidimensional and complex problem since it requires the knowledge and experience of several disciplines. The effectiveness of risk management can be analyzed, inviting to the action through weakness identification of the urban area. This article proposes a methodology based on the morphological analysis to support the decision-making on disaster risk management, taking as a starting point the results of a holistic evaluation of the seismic risk. The results of the holistic evaluation of risk are achieved aggravating the physical risk using the contextual conditions, such as the socio-economic fragility and the lack of resilience. In consequence, the risk mitigation can be performed through the reduction of the potential damage and consequences involved; and the improvement of social conditions. The proposed methodology allows prioritizing the risk reduction strategies according to i) performance level of component indicators involved into the Disaster Risk Management index, DRMi; ii) physical risk factors dependent from the potential damages, and iii) aggravating factors involved in the aggravating coefficient. Moreover, it involves 35 strategies to reduce the physical risk and the aggravating social conditions of the urban area. The proposed methodology has been applied to the city of Mérida (Venezuela), located within an area of high seismic activity. The performance level of the indicators involved in the DRMi was evaluated by a survey to local experts. As a result, eleven strategies have been identified to reduce the potential damage and to improve the social conditions of this city.Peer ReviewedPostprint (author's final draft

Automatic manhole extraction from MMS data to update basemaps

Basemaps are the main resource used in urban planning, building and infrastructure asset management. Therefore, they must be accurate and up to date to better serve citizens, contractors, property owners and town planning departments. Traditionally, they have been updated by aerial photogrammetry, but this is not always possible and alternatives need to be sought. In such cases, a useful option for large scales is the mobile mapping system (MMS). However, automatic extraction from MMS point clouds is limited by the complexity of the urban environment. Therefore, the influence of the urban pattern is analysed in three zones with varied urban characteristics: areas with high buildings, open areas, and areas with a low level of urbanization. In these areas, the capture and automatic extraction of 3D urban elements is performed using commercial software, which is useful for some elements but not for manholes. The objective of this study is to establish a methodology for extracting manholes automatically and completing hidden buildings' corners, in order to update urban basemaps. Shape and intensity are the main detection parameters for manholes, whereas additional information from satellite image Quickbird is used to complete the buildings. The worst rate of detection for all the extracted urban elements was found in areas of high buildings. Finally, the article analyses the computing cost for manhole extraction, and the economic cost and time consume of the entire process, including the proposed methodolgy using an MMS point cloud and the traditional survey in this case.Peer ReviewedPostprint (updated version

Sostenible - No sostenible

Esta breve contribución, dentro del bloque temático “Iniciativas-motor de cambio”, contiene una idea principal: la insostenibilidad intrínseca del desarrollo humano. Afortunadamente, esta “no-sostenibilidad” es sólo un tema de nomenclatura que se refiere al significado literal del término; no es un problema de fondo que cuestione la necesidad de desarrollar políticas y estrategias orientadas al Desarrollo Humano “Sostenible” (DHS).Peer Reviewe

Spatial data infrastructure (SDI) for inventory rockfalls with fragmentation information

The version of record of this article, first published in Natural Hazards is available online at Publisher's webside: https://doi.org/10.1007/s11069-022-05282-2The fragmentation phenomenon has a significant effect on rockfall risk assessment. This information is difficult to obtain, but it is key to improving rockfall modelling. For this reason, the RockModels team has gathered data on the fragmentation of several natural events since 2014 that nowadays wants to share them with professionals, academics and stakeholders. The best way for the dissemination of this information is the use of standard or data specifications in order to be interoperable. A fragmentation rockfall database has been created using all the gathered information, according to the INSPIRE Natural Hazard Area Data Specification currently in force. However, new tables have had to be added, since this specification does not consider fragmentation data. There are currently 6000 records of geometries of source areas, envelopes, deposits and mostly individual blocks. A web mapping application, with an automatic function for coordinate reference system transformation, has been created to facilitate access to the spatial database information. All that was developed on open-source software such as OpenLayers JavaScript library, database (PostGre-PostGIS) and the map generating Web Map Service (GeoServer). As more data are collected, the database can be easily updated and the new information will be published. Moreover, to improve data interpretation, a future task is to incorporate 3D models on the web application. The existence of this public database will facilitate research and advance in knowledge of this kind of natural hazards.Peer ReviewedPostprint (published version