# A Critical Review of Flood Risk Management and the Selection of Suitable Measures
## 3 Risk-Based Flood Management
### Risk Parameters  
Risk-based assessment evaluates flood measurements based on potential impacts, while reducing negative impacts of floods, such as socioeconomic and environmental factors. This method provides a logical ground to shortlist and finalize flood management options. Understanding risk concepts, elaboration of the role of the river process, and societal activities should be considered during the assessment. Risk can be broadly defined as \"an estimation of expected results connected to a hazard\".  
\[\text{Risk ($\$\ year^{-1}$) = Probability (year^{-1}$) \times Consequences ($\$)} \tag{1}\]  
Also, the risk is a function of how vulnerability interacts with hazard or vice versa.  
\[\text{Risk ($\$\ year^{-1}$) = Hazard (m year^{-1}$) \times Vulnerability ($\$\ m^{-1}$)} \tag{2}\]  
The above-stated term indicates that the hazard itself is not the only cause for risk induction. Everyday vulnerability and hazards shape trends of rising risk, which can end in a catastrophe arising from an exceptionally natural incident [54]. Therefore, two independent variables are considered for risk analysis--hazard and vulnerability. In flood management, the term \"hazard\" indicates the occurrence of a high-water-level event with a given probability of exceedance [55]. Thus, the hazard may be classified by its intensity and probability.  
\[\text{Hazard (m year^{-1}$) = Probability (P) (year^{-1}$) \times Intensity (I) (m)} \tag{3}\]  
Probability can be defined as the chance of a hazard to occur that can be defined annually for a flood event. While some negative intensity features (depth, velocity, etc.) of hazards cause damage, vulnerability is the outcome of susceptibility and exposure.  
\[\text{Vulnerability ($\$\$ m^{-1}$) = Susceptibility (S) (m^{-1}$) \times Exposure (E) ($\$)} \tag{4}\]where people and value currently exist in an under-threat region is known as exposure. Susceptibility is generally defined as the relative loss function [56; 57]. The ability to recognize the losses from the hazard is susceptibility. The extent of loss is based on the susceptibility of vulnerable items and life, and indeed the magnitude of hazard. In order to comprehend the role of both sides, risk in terms of vulnerability and hazard needs to be articulated, as illustrated in Equation (2). Thus, we get Equation (5) by substituting vulnerability and hazard by their components in Equation (2). Likewise, expressing probability alone will result in Equation (6).  
\[\text{Risk}=[\text{P}\times\text{I}]\;(\text{m year}^{-1})\times[\text{S} \times\text{E}]\;(\text{$\$}\text{$\$}\text{$\}\text{$\}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}\text{$\}}\text{$\}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}}\text{$ \tag{5}\]  
\[\text{Risk}=\text{P}\times[\text{I}\times\text{S}\times\text{E}]\;(\text{$\$} \text{$\$}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\}\text{$\} \text{$\}\text{$\}\text{$\}\text{$\}}\text{$\}\text{$\} \tag{6}\]  
If the chance of the mutual interaction of vulnerability and hazard is considered separately, the consequences are definitely as a result of a hazard's intensity, and the total exposures of assets and how much they accept the damage from the hazard (the susceptibility). It can be observed that Equation (6) is an elaborated expression of Equation (2). A graphical demonstration is shown in Figure 3 below.