18. 02. 2019

Technical networks, urban resilience and pragmatism

BY JEAN-MARIE CARIOLET AND MARC VUILLET, Ecole des ingénieurs de la ville de Paris

Linear urban infrastructures, such as technical networks, roads and embankments, play a major role in urban resilience. Many recent disasters have shown their role as “barriers” to hazards, this being the case of dykes and drainage networks, or contrariwise as disseminators of impacts through the potential dysfunctions and cascading effects within urban networks such as energy grids, telecommunications and transport networks, etc.

Several responses have been intended to deal with these phenomena: assessment of infrastructures vulnerability to hazards, assessment of the dysfunction duration depending on the hazard duration and predictability, facilities sheltering plans elaborated by each network operators. In addition to such solutions, there is a need for operators to take dependencies of their infrastructures on other infrastructures and/or services into account in the perspective of their functioning as well as of their operating resumption (for instance, water supply equipment may be dependent on power and the later could potentially depend on telecommunications, etc.).

Several approaches have been suggested for modelling interdependent networks in order to assess their resilience, that means their capability to absorb a hazard (continue operating, in normal or degraded mode) and recover from it so as to resume acceptable operating functions in a reasonable timing. To tackle the challenge of modelling the functioning of these networks, given their multiple components and interconnections as well as their dynamic properties, the choice of the most suitable approach and its implementation are complex problems. First, there is a need to clearly define the scope of the study, the hazard(s), the detail levels within services, keeping in mind that the choice of these levels must allow supporting decision-makers without burying them within an infinite amount of details. Then, it must be important to identify which decision-makers will lead the approach relying on the expressed needs.

The main requirement is to initiate a collaborative dynamic facilitating in a first instance a better understanding of cascading failures which are likely to occur among services in order to reduce them and/or their effects. This will also allow to familiarise the stakeholders of crisis management with a kind of common language and to pre-identify which experts from which areas of expertise should be mobilised in the case where a crisis would tend to take any form, crisis management being an exercise with countless forms and uncertainties. Create and engage a community of “Players” to tackle resilience from a holistic point of view is key.

The second iteration of Hazur assessment conducted within the framework of H2020 RESCUE project aims at addressing these challenges. It capitalises on the results of the first test of the method which allowed to initiate the approach in 3 different cities (Barcelona, Bristol and Lisbon) and to build a first global situational analysis of vulnerabilities and interdependencies after defining (or identifying) players involved and services.

This second iteration deals with the mentioned issues, taking into account the cascading effects with the aid of Hazur tool that aims at working on grey areas identified as with high priority by the “Players”, and capitalising the results achieved during the initial assessment. At the same time, it will take into account the declination of climate change scenarios at a local level and the knowledge gained from the impacts of hazards on networks which are refined through sectorial studies and models, sometimes linked within the framework of the detailed analysis from work packages 2 and 3.

The Hazur procedure will be improved thanks to a better concertation seeking to define the role of each stakeholder with regard to precise issues: to integrate results from other work packages, to take advantage of information gathered during the first assessment, to determine the adequate level of modelling using well contextualised new data and, last but not least, to have the vision of how to develop a replicable tool for cities.