Tsunami evacuation modelling as a tool for risk reduction: application to the coastal area of El Salvador

Following with the results of our research on tsunami hazard and risk at El Salvador, I want to share with you our last publication of 2013. This paper has been published in Natural Hazards and Earth System Sciences (link) with the self-explanatory  title: “Tsunami evacuation modelling as a tool for risk reduction: application to the coastal area of El Salvador”. The leader of the work is Pino González-Riancho; researcher and Ph.D. candidate at the “IH Cantabria” Insitute of Environmental Hydraulics.

Advances in the understanding and prediction of tsunami impacts allow the development of risk reduction strategies for tsunami-prone areas. This paper presents an integral framework for the formulation of tsunami evacuation plans based on tsunami vulnerability assessment and evacuation modelling. This framework considers (i) the hazard aspects (tsunami flooding characteristics and arrival time), (ii) the characteristics of the exposed area (people, shelters and road network), (iii) the current tsunami warning procedures and timing, (iv) the time needed to evacuate the population, and (v) the identification of measures to improve the evacuation process. The proposed methodological framework aims to bridge between risk assessment and risk management in terms of tsunami evacuation, as it allows for an estimation of the degree of evacuation success of specific management options, as well as for the classification and prioritization of the gathered information, in order to formulate an optimal evacuation plan. The framework has been applied to the El Salvador case study, demonstrating its applicability to site-specific response times and population characteristics.

Tsunami evacuation planning framework proposed in the work.

The methodology proposed has been applied to the area of Barra de Santiago – Acajutla in El Salvador. This area is characterized by a 9 km-long sand spit that protects the estuary (Estero El Zapote) of the Aguachapío, Guayapa and El Naranjo rivers. The wetland includes an important mangrove area and belongs to the Complejo Barra de Santiago ANP (Protected Natural Area). According to the census (VI Censo de Población y V de Vivienda, DIGESTYC, 2007) and the hazard modelling results, the number of people located in the tsunami-flooded area is around 3300, 75 % being located on the sand spit (Barra de Santiago canton), which was affected by the tsunami of 1902 and where, according to the local knowledge, only 5 persons survived the event.

The evacuation modelling for the current response time of 45 min (i.e. warning time 30 min, reaction time 15 min) highlighted that improvements to the warning process must be made to ensure the success of the evacuation, as most of the coastal communities would be reached by the tsunami before being warned about it. A reduction of 15 min in the response time (a response time of 30 min) showed that a higher percentage of populations evacuates (proving the importance of working on this issue); however, the communities located closer to the coastline would not be able to reach the safe areas. For these communities an attempt to identify alternative measures to ensure their evacuation is proposed, such as building new evacuation routes and new vertical shelters. These combined measures (reducing response time and reducing distances to travel) have been demonstrated to be useful for achieving the desired results.

Evacuation time modelling
Evacuation time modelling for a response time of 30 min and proposal of alternatives for critical areas.

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