Assessing physical vulnerability in large cities exposed to flash floods and debris flows: the case of Arequipa (Peru)

Abstract

International audienceUnderstanding the physical vulnerability of buildings and infrastructure to natural hazards is an essential step in risk assessment for large cities. We have interpreted high spatial resolution images, conducted field surveys, and utilized numerical simulations, in order to assess vulnerability across Arequipa, south Peru, close to the active El Misti volcano. The emphasis of this study was on flash floods and volcanic or non-volcanic hyperconcentrated flows, which recur on average every 3.5 years across the city. We utilized a geographic information system to embed vulnerability and hazard maps as a step to calculate risk for buildings and bridges along the Río Chili valley and two tributaries. A survey of ~1,000 buildings from 46 city blocks, different in age, construction materials, and land usage, provided architectural and structural characteristics. A similar survey of twenty bridges across the three valleys was based on structural, hydraulic, and strategic parameters. Interpretation of high spatial resolution (HSR) satellite images, which allows for quick identification of approximately 69 % of the structural building types, effectively supplemented field data collection. Mapping vulnerability has led us to pinpoint strategic areas in case of future destructive floods or flows. Calculated vulnerability is high if we examine structural criteria alone. We further consider physical setting with the most vulnerable city blocks located on the lowermost terraces, perpendicular or oblique to the flow path. Statistical analysis conducted on 3,015 city blocks, considering nine criteria identified from HSR images, indicated that building-type heterogeneity and the shape of the city blocks, along with building and street network density, are the most discriminant parameters for assessing vulnerability

Evaluación de la vulnerabilidad de edificaciones ante la génesis de lahares: Caso de estudio en la población de Santiago Xalitzintla, en el flanco NE del volcán Popocatépetl (México)

“…Sin embargo, para localidades más grandes, es recomendable reducir el tamaño de la muestra identificando primero la región afectada por la amenaza (en este caso, la probabilidad de un lahar) y después proceder a evaluar la vulnerabilidad de las edificaciones en dicha área. Así por ejemplo, en el trabajo de Thouret et al (2014), se evalúa la vulnerabilidad física de grandes ciudades expuestas a flujos de gravedad, y centra su estudio en Arequipa (Perú).…”

Computational Bottom-Up Vulnerability Indicator for Low-Income Flood-Prone Urban Areas

“…The variables representing the three components of vulnerability [22]-(i) exposure to a hazard event (E), (ii) susceptibility (S), and (iii) resilience (R)-were selected from the literature [14,[70][71][72][73][74], refined, and qualified in workshops with 13 experts in the fields of disaster risk reduction, geology, civil engineering, environmental engineering, and social sciences. The selected variables (Table 1) were included into a survey to collect information from each household.…”

Quantifying lahar damage using numerical modelling

“…Studies simplifying vulnerability into a relative index use a 50 combination of qualitative and quantitative metrics obtained through building surveys, interpretation of remote sensing data and GIS techniques to map and analyse vulnerability on a large scale (e.g. Lavigne, 1999;Künzler et al, 2012;Galderisi et al, 2013;Thouret et al, 2013;Thouret et al, 2014;Ettinger et al, 2015). These methods can be applied to understand and highlight spatial patterns in vulnerability; however, as a relative measure, they cannot provide guidance on expected damage for any specific event.…”

“…Zanchetta et al, 2004;Custer and Nishijima, 2015;Jenkins et al, 2015). However, building typologies are affected by socio-economic, cultural and institutional conditions 65 (Künzler et al, 2012) and environmental factors such as local elevation, distance from main channels and orientation affect flow depths and velocities near buildings (Thouret et al, 2014). These issues cause direct vulnerability relationships to be site-specific and requires detailed investigation of regions at risk to examine the relative importance of hazard, exposure and vulnerability on building loss.…”