**5. The challenges of flood modelling and vulnerability assessment in the Lagos metropolis of Nigeria**

Given the general merits of flood modelling and assessment of vulnerability to flooding and the specific roles they can play towards flood risk reduction in the Lagos metropolis of Nigeria (refer to [42]), it is important to identify the factors that potentially constrain their application. In view of this, the author conceived and discuss the following issues:

#### **5.1 Issues on data**

The fact that flood modelling and assessment of vulnerability to flooding require sufficient and accurate data to implement suggests paucity of data as mostly constraining such operations. For the Lagos area, it can be argued that issues relating to relevant data can be likened to a total mirage ranging from abject paucity, inaccuracy and limited access. A typical example is demography for which two key sources (2006 National Population Census and Lagos State Digest of Statistics) quoted different figures representing the Lagos region. Equally complicating is media reporting which has been inconsistent in many instances [44]. Although high resolution LiDAR data is now available for the area, access to the dataset for flood modelling and assessment of vulnerability is been constrained by cost.

**195**

*Flood Risk Analysis for Critical Infrastructure Protection: Issues and Opportunities in Less…*

(for example Climate Change Adaptation (CCA) and Disaster Risk Reduction (DRA)) which promote the development of integrated methodologies subject to living with floods rather than fighting them [45, 46]. Invariably, such methodologies seem to require in-depth understanding of the drivers of flood risk while their practicability appears to suit ideal situation favoured by easy access to relevant datasets and technical requirements. However, these methodologies often lack sufficient flexibilities for application to external case studies such as the DCs. To circumvent such methodology inflexibility, it is imperative that new methodologies are developed. For the Lagos area, it can be argued that the development of new methodologies with sufficient capacity to support assessment of vulnerability to flooding and flood modelling can be easily undermined by the underlying concepts and theories which

Flood risk reduction is a key concern for major environmental research themes

Expectations are increasing for more efficient methodologies with regards to tackling flooding and the risks it poses [47]. Based on this, improving on the functionality of existing methodology has become a popular hypothesis recently. Whilst this assumption has been affirmed in many cases, intuitively, an important concept such as flood modelling underlines the need to understand the basic components that limits existing methodologies [48, 49]. Within the context of flood modelling, existing methodologies (especially for the physically based numerical flood models) lead to models that are computationally expensive, often unstable/conditionally stable requiring a certain CFL condition (Courant-Freidrichs-Lewy condition), which prescribes small time steps leading to high computation burden. Besides, some of these models lack extensive calibration due to insensitivity to certain parameterisation. For the Lagos metropolis of Nigeria, it is argued that the means to overcome these challenges present a critical consideration which undermines flood modelling in the area, although the Lack of funds to acquire commercial codes along with their

technical assistance can also have a resistive impact on flood modelling [9].

full preparedness to deal with the challenges of flooding is uncertain.

Flood risk reduction within the context of living with floods is strengthened by robust legislation towards environmental management, intensive research and adaptation of human population to the hazard. Nigeria among many DCs is characterized by weak legislation towards hazard management [50]. This arguably impacts negatively on the inclusion of more robust approaches such as flood modelling and assessment of vulnerability to tackling flooding and the challenges it poses. As argued by Oshodi [32], due to the weak legislation and poorly implemented policies regarding hazard risk and environmental sustainability in the Lagos area,

Flood modelling and assessment of vulnerability to flooding required to effectively tackle flooding underpin sustainable development [11]. Within the context of sustainable development, every society aspires towards meeting human development goals while sustaining the ability of natural systems to continue to provide

*DOI: http://dx.doi.org/10.5772/intechopen.95364*

are generally inductive based on ontological perspective.

**5.2 Issues on theories and concepts**

**5.3 Issues on existing methodologies**

**5.4 Issues on legislation and policy**

**5.5 Issues on sustainable development**

*Flood Risk Analysis for Critical Infrastructure Protection: Issues and Opportunities in Less… DOI: http://dx.doi.org/10.5772/intechopen.95364*

### **5.2 Issues on theories and concepts**

*Issues on Risk Analysis for Critical Infrastructure Protection*

population to cope with floods.

Lagos area [43].

**5.1 Issues on data**

**Lagos metropolis of Nigeria**

and discuss the following issues:

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

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

**5. The challenges of flood modelling and vulnerability assessment in the** 

Given the general merits of flood modelling and assessment of vulnerability to flooding and the specific roles they can play towards flood risk reduction in the Lagos metropolis of Nigeria (refer to [42]), it is important to identify the factors that potentially constrain their application. In view of this, the author conceived

The fact that flood modelling and assessment of vulnerability to flooding require sufficient and accurate data to implement suggests paucity of data as mostly constraining such operations. For the Lagos area, it can be argued that issues relating to relevant data can be likened to a total mirage ranging from abject paucity, inaccuracy and limited access. A typical example is demography for which two key sources (2006 National Population Census and Lagos State Digest of Statistics) quoted different figures representing the Lagos region. Equally complicating is media reporting which has been inconsistent in many instances [44]. Although high resolution LiDAR data is now available for the area, access to the dataset for flood modelling and assessment of vulnerability is been constrained

**194**

by cost.

Flood risk reduction is a key concern for major environmental research themes (for example Climate Change Adaptation (CCA) and Disaster Risk Reduction (DRA)) which promote the development of integrated methodologies subject to living with floods rather than fighting them [45, 46]. Invariably, such methodologies seem to require in-depth understanding of the drivers of flood risk while their practicability appears to suit ideal situation favoured by easy access to relevant datasets and technical requirements. However, these methodologies often lack sufficient flexibilities for application to external case studies such as the DCs. To circumvent such methodology inflexibility, it is imperative that new methodologies are developed. For the Lagos area, it can be argued that the development of new methodologies with sufficient capacity to support assessment of vulnerability to flooding and flood modelling can be easily undermined by the underlying concepts and theories which are generally inductive based on ontological perspective.

#### **5.3 Issues on existing methodologies**

Expectations are increasing for more efficient methodologies with regards to tackling flooding and the risks it poses [47]. Based on this, improving on the functionality of existing methodology has become a popular hypothesis recently. Whilst this assumption has been affirmed in many cases, intuitively, an important concept such as flood modelling underlines the need to understand the basic components that limits existing methodologies [48, 49]. Within the context of flood modelling, existing methodologies (especially for the physically based numerical flood models) lead to models that are computationally expensive, often unstable/conditionally stable requiring a certain CFL condition (Courant-Freidrichs-Lewy condition), which prescribes small time steps leading to high computation burden. Besides, some of these models lack extensive calibration due to insensitivity to certain parameterisation. For the Lagos metropolis of Nigeria, it is argued that the means to overcome these challenges present a critical consideration which undermines flood modelling in the area, although the Lack of funds to acquire commercial codes along with their technical assistance can also have a resistive impact on flood modelling [9].

#### **5.4 Issues on legislation and policy**

Flood risk reduction within the context of living with floods is strengthened by robust legislation towards environmental management, intensive research and adaptation of human population to the hazard. Nigeria among many DCs is characterized by weak legislation towards hazard management [50]. This arguably impacts negatively on the inclusion of more robust approaches such as flood modelling and assessment of vulnerability to tackling flooding and the challenges it poses. As argued by Oshodi [32], due to the weak legislation and poorly implemented policies regarding hazard risk and environmental sustainability in the Lagos area, full preparedness to deal with the challenges of flooding is uncertain.

#### **5.5 Issues on sustainable development**

Flood modelling and assessment of vulnerability to flooding required to effectively tackle flooding underpin sustainable development [11]. Within the context of sustainable development, every society aspires towards meeting human development goals while sustaining the ability of natural systems to continue to provide

the natural resources and ecosystem services upon which the economy and society depend [51, 52]. Despite much attention which it has received, sustainable development in the DCs remains uncertain and almost unrealistic due to a number of factors for examples: gender inequality, poverty, weak legislative impetus, governance and political will, sluggish judicial administration and access to justice, corruption, asymmetric corporate social irresponsibility and poor access to information, and technical knowledge [53, 54]. For the Lagos area of Nigeria, poor public participation in planning, capacity building, and integration of information technology into planning practice are key factors that constrain sustainable development [55]. Poor public participation can be revealed mainly in the poor awareness of flooding among the wider public, and lack of compliance to environmental laws. To investigate the vulnerability to flooding of social systems for example, relevant information is often derived from public survey and responses to questionnaire. Arguably, inaccurate or uncorrelated responses from questionnaires which jeopardize the outcomes of such investigations can result from poor awareness of flooding.
