How to manage and mitigate disaster risk in urban areas?

The importance of risk mitigation in urban conservation

Risk mitigation is assumed today as a top priority in the international political agenda. Recent natural disasters raised the awareness of governments and scientists and have let to the search for more efficient and effective strategies to manage and mitigate risk, particularly in urban areas.

These strategies are typically focused on identifying the most vulnerable zones within urban areas (often associated to historical centres) in order to enhance both the response and recovery capacity in the sequence of a catastrophic event.

Neglecting the implementation of adequate risk mitigation measures significantly reduces such capacity. The proper identification of both the external hazards that can potentially affect a site and the vulnerability of the building stock is a fundamental prerequisite to guarantee an effective post-event response.

A probabilistic point of view

The assessment of these two elements – external hazards that can potentially affect a site (such as natural disasters) and the vulnerability of the building stock – is affected by uncertainties of aleatory and epistemic nature. It is fundamental to bear in mind that risk quantification is a highly probabilistic process, which mean that risk results should always be analysed from a probabilistic point of view.

Tools and Methodologies

When performing vulnerability assessment of large numbers of buildings and over an urban area, the resources and quantity of data required may be enormous and consequently the use of less onerous inspection and recording tools is more practical.

Following the same logic, methodologies for vulnerability assessment at the urban scale should be based on few parameters, typically of empirical nature, defined through the knowledge of the effects of past earthquakes, which can be treated statistically.

The definition and nature of the approach (qualitative and quantitative) naturally condition the formulation of the methodologies and the level at which the evaluation is conducted, from the expedite evaluation of buildings based on visual observation to the most complex numerical modelling of single buildings, see image below:

Another aspect that is worth noting in this context is that risk management of urban areas is, in many cases, undertaken without the use of a general planning tool, such as a Geographic Information System (GIS). A primary consequence of this issue is that technicians and decision makers do not acquire a global perspective of the area under analysis, which can seriously compromise the effectiveness of eventual rehabilitation strategies and risk mitigation measures.

Risk mitigation should be based on a comprehensive knowledge on buildings’ characteristics and vulnerability

This way it is possible to define more proficient mitigation strategies and to outline strengthening interventions that can contribute to reduce specific vulnerability and, consequently, to increase overall urban resilience.

From the risk modelling and analysis viewpoint, it is worth remarking that, if on the one hand it is fundamental to properly address uncertainties and inconsistencies often concealed in estimations, avoiding this way disseminating erroneous conclusions and biased results, on the other hand, however, it is not less important that risk intensity measures or indicators can be easily understood and interpreted by citizens, stakeholders and civil protection authorities.