## 2 Materials and Methods
### Frequency Ratio Method  
The FR technique, which represents the likelihood of the occurrence of a particular feature, was first introduced by [PERSON] [72; 73; 74]. It should be noted that under the FR model, a class with a higher value indicates a class's greater potential for an incident (such as a flash flood, landslide, or groundwater potentiality). In the context of this study, it suggests that a place is more susceptible to artificial recharging through FSM. FR is calculable as follows:  
\[\text{FR}=\left(\frac{\text{FSN}}{\text{FS}_{\text{total}}}/\frac{\text{A}}{ \text{A}_{\text{total}}}\right) \tag{1}\]  
Figure 6: Parameters used for FR modelling: (**a**) elevation, (**b**) slope, (**c**) aspect, (**d**) LU/LC, (**e**) lithology, (**f**) distance from main streams, (**g**) stream density, (**h**) TWI index, (**i**) TRI and (**j**) surface runoff.  
where FSN indicates the total number of FSM locations, FS total displays all FSM locations, A shows the total number of FSM points in each category of variables, and total displays all cells in the region under study. The term FR denotes the frequency ratio for various FSM conditioning factor classes. The following equation is used to determine each pixel's final FR value [25; 75; 76]:  
\[\text{FSMR}=\sum\text{(FR)}j\text{ ($j$ = 1, 2,....... n)} \tag{2}\]  
where \(j\) is various FSM conditioning factors, and FSMR is the final FR value for each individual pixel.  
Each controlling factor's FR value was calculated using ArcGIS and Microsoft Excel and its importance in flood susceptibility (Table 1). Accordingly, elevation, slope, aspect, LULC, lithology, stream distance, and stream density had the highest importance values in the modelling process. On the other hand, TWI, TRI, and surface runoff had the least important values. Using ArcMap 10.7, the FSM map was produced using the FR approach by integrating the FR layers of the controlling parameters (Equation (3)).  
\[\text{GFSM}=\sum_{i=1}^{n}\text{FR} \tag{3}\]  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**FSM Conditioning Factors** & **Classes** & **\% of Domain** & **\% of FSM Points** & **FR** \\ \hline \multirow{4}{*}{Slope} & 0–10 & 6.0 & 39.7 & 8.1 \\  & 10–20 & 10.4 & 55.3 & 4.8 \\  & 20–30 & 20.1 & 0.0 & 0.0 \\  & \textgreater{}30 & 61.5 & 0.0 & 0.0 \\ \hline \multirow{4}{*}{Elevation} & \textless{}60 & 45.2 & 92.7 & 2.0 \\  & 60–93 & 8.1 & 68.3 & 2.7 \\  & 94–110 & 46.6 & 58.0 & 1.9 \\  & 120–140 & 20.9 & 54.7 & 1.7 \\  & 150–160 & 60.3 & 34.0 & 1.5 \\  & 170–190 & 18.8 & 0.0 & 0.0 \\  & \textgreater{}190 & 35.8 & 0.0 & 0.0 \\ \hline \multirow{4}{*}{Aspect} & Flat & 20.9 & 4.7 & 1.5 \\  & North & 60.3 & 92.0 & 0.5 \\  & Northeast & 18.8 & 3.3 & 0.2 \\  & South & 35.8 & 0.0 & 0.0 \\  & Southeast & 2.3 & 0.0 & 0.0 \\  & West & 11.5 & 0.0 & 0.0 \\ \hline \multirow{4}{*}{LULC} & Urban & 23.2 & 35.0 & 2.1 \\  & Vegetation & 10.5 & 11.7 & 1.4 \\  & Bare Land & 60.0 & 55.3 & 0.9 \\  & Water & 4.3 & 0.0 & 0.0 \\ \hline \multirow{4}{*}{Lithology} & Sandstone & 30.5 & 70.3 & 0.2 \\  & Loose sand & 10.9 & 45.3 & 5.8 \\ \cline{1-1}  & Sand and gravel & 7.5 & 60.1 & 5.3 \\ \cline{1-1}  & Sandstone marl & 49.1 & 0.0 & 0.0 \\ \cline{1-1}  & White limestone & 3.9 & 22.0 & 6.6 \\ \hline \multirow{4}{*}{Distance from streams (m)} & \textless{}430 & 40.0 & 68.7 & 2.7 \\  & 440–850 & 24.8 & 24.0 & 1.0 \\ \cline{1-1}  & 860–1300 & 14.8 & 2.7 & 0.2 \\ \cline{1-1}  & 1400–1700 & 9.0 & 2.7 & 0.3 \\ \cline{1-1}  & 1800–2100 & 11.3 & 2.0 & 0.2 \\ \cline{1-1}  & \textgreater{}2200 & 12.0 & 3.1 & 0.1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Frequency ratio (FR) outputs of the controlling factors layers used for flood suitability mapping.