**4. Flood modelling and assessment of vulnerability to flooding for the Lagos metropolis of Nigeria**

Flood risk reduction is fundamentally a knowledge-driven ideology that shapes the pathway towards living with floods. Key knowledge that drives this idea is often based on flood risk/hazard maps, public opinions and specialist judgement on flooding. Within this perspective, flood modelling which predicts flood data (mainly flood water depth, duration and extent, as well as depth-averaged velocities) essentially needed for flood risk/hazard analyses, mapping and assessment plays significant roles [36, 37]. Conceptually, flood modelling may be perceived as a scientific technique that numerically or analytically solves relevant governing mathematical equations and generates computer algorithms and codes for fast, continuous and routine simulation of flood data [9]. Quick, continuous and routine provisions of flood data appear to undermine ground survey methods and remote sensing technologies, thus most evidently highlighting the relevance of flood modelling.

*Issues on Risk Analysis for Critical Infrastructure Protection*

appreciated. Typically, the hazard which has been generally attributed to climate change and poor urban planning affects hundreds of thousands of people (mostly through homelessness, physical injuries, mortality, spread of diseases and emotional trauma), destroys chains of urban infrastructure and disrupts economic activities [14, 24]. Fiscal losses caused by the hazard in the area amount to millions of US dollars [25]. Although fluvial and coastal flooding occurred in the early days of flooding – i.e. in the early 1960s – pluvial floods resulting from prolonged rainfall which overwhelms urban drainage facilities and soil infiltration capacity are now more widespread. Such floods usually recur annually between the months of March and October (but usually more severe in July) with considerable environmental and socio-economic impacts [26]. These floods which have triggered concerns for environmental mismanagement, urgent humanitarian needs and services, primary health delivery, solid waste management, urban development and governance, and the resilience of the general public within the area are claimed to be more severe for Lagos Island, Apapa, Ikeja, Mushin, Surulere and parts of Ikorodu [16, 26–29]. The magnitude of flooding experience in the Lagos region of Nigeria is highlighted in **Figure 2(a-d)** below. A typical example of flooding event in Lagos is the July 2011 flooding, caused by a heavy rainfall that lasted 17 hours. The flood affected more than 10 thousand people with deaths exceeding 100 and a range of damage including public infrastructure such as roads, bridges and schools. Houses were submerged by flood water while lots of properties including vehicles were destroyed due to the intensity of the flood. An estimated economic loss of about 50 billion

*Examples of flooding scenes in the Lagos metropolis of Nigeria: (a) living room submerged by flood water, (b) residential building submerged, (c) local community affected by flood waters, and (d) expressway* 

*overwhelmed by flood water. Source: Online images of flooding in Lagos, Nigeria.*

**3. Summary of current efforts towards tackling flooding in Lagos**

For appraisal of current approaches to flood risk management in Lagos city by public and private sectors and the implications of such approaches within the

**192**

**Figure 2.**

Naira (\$US 320 million) was incurred [30].

For the Lagos area, besides the importance of quick, continuous and routine provision of flood data, it is pertinent to realize the specific roles which flood modelling can play towards flood risk reduction and these includes: (1) to align the goals of flood risk management in the Lagos areas with the objectives of such roles in other places such as the United States, United Kingdom and the Netherlands, (2) to pave the way for overcoming the various hassles associated with flood modelling generally such as computation complexity and model instability/conditional stability, (3) to strengthen the means of improving flood awareness among urban residents and other stake holders through flood risk/hazard mapping, and (4) to combine with vulnerability assessment in order to build the capacity of a wider population to cope with floods.

Vulnerability is clearly a relevant concept in disaster/risk management and it suggests the propensity to which a system, subsystem or systems component can be adversely affected by a stressor [38]. System, subsystem or systems component refer to human populations and/or critical infrastructure that appear to be in harm's way during flood hazard occurrence which is the reason why exposure, sensitivity and adaptive capacity are often considered in the course of analysing vulnerability [38, 39]. In the Lagos metropolis of Nigeria, the issue of vulnerability to flooding is critical given that urbanization and rapid population growth which both trigger and increase slum development and development on flood prone areas [40]. However, this odd scenario has not been sufficiently tackled with adequate knowledge of vulnerabilities of social systems to flooding and the factors that influence such vulnerabilities. Few studies that considered vulnerability to flooding in Lagos are limited in scope, constrained by paucity of quality data and narrowed discussions down to small areas [15, 16, 41, 42]. It can be shown that results obtained from analysing vulnerability to flooding at such small scales cannot be generalized for the Lagos area [43].
