An urban form response to disaster vulnerability: improving tsunami evacuation in two Chilean cities

© 2015 Dr. Jorge Enrique León CanalesGlobally, the number of nature-originated catastrophes has steadily increased during the last five decades. At the same time, cities have become ‘hot-spots’ of disasters, due to factors such as overpopulation, fast expansion of informal settlements, and lack of governance. To face these challenges, the role of built environment disciplines such as urban planning and urban design in disaster mitigation is increasingly recognised. While disaster management activities such as recovery, preparedness and response have been examined in the built environment disciplines, a strong emphasis remains on long-term risk reduction policies, such as land-use regulations and building codes. This research suggests that built environment disciplines provide opportunities for the integration and development of a wider set of tools for the improvement of response capacities of disaster-prone communities. Specifically, it is argued that integrating response capability approaches into the urban design of public space is especially important in the case of rapid onset disasters. With this purpose, this research examines the case of near-field tsunami evacuations in two Chilean cities, Iquique and Talcahuano (the latter severely affected by a tsunami in 2010). In each of the case studies, this research undertakes three phases of analysis, using a mixed-method approach (including a literature review, computer-based modelling and fieldwork). Firstly, it analyses the existing conditions for evacuation (e.g. the identification of the most suitable urban spaces for sheltering, the required times for clearance, and the critically hazardous areas). Secondly, the research proposes macro- and micro-scale urban form changes to improve these conditions (e.g. the creation of vertical evacuation points, changes in the urban street patterns, and streetscape improvements). Thirdly, it assesses the possible impacts of the macro-scale changes by using a quantitative tool, an agent-based computer model. This research then undertakes a cross-case analysis of the case studies’ outcomes, enhanced with relevant lessons learnt from other tsunami-prone contexts around the world. This research’s findings demonstrate that Iquique and Talcahuano remain significantly vulnerable to near-field tsunamis, as large parts of their populations and essential urban activities are located in flood areas. Moreover, an emergency evacuation of these cities could not be completed during the expected available time of 20 minutes. This research exposes the antecedent conditions that have cumulatively contributed to this vulnerability: geophysical characteristics of tsunamis, urban development patterns, urban form characteristics, cascading consequences associated with tsunamigenic earthquakes, and social and institutional characteristics. The research’s findings also show that the proposed macro-scale changes might significantly reduce the total evacuation times (up to 22%). Furthermore, the suggested micro-scale changes to urban space could increase safety and liveability. Lastly, this research proposes a set of seven urban design principles for improving tsunami evacuation in the public space: maximize proximity to safe areas, allow for an expeditious population displacement, ensure evacuees’ safety, foster built environment’s redundancy, mainstream risk reduction for sustainability and suitability, support autonomous responses, and strengthen population’s memory. These principles provide an original and valuable contribution to the disaster risk reduction field of study, as they bring about a real-world tool for improvement, and also a framework for future research in other tsunami-prone contexts around the globe