## 4 Results
### Assessment of Inundation  
#### 4.2.1 Inundation Due to Peak Rainfall  
Figure 7 presents the area-averaged monsoon rainfall across the study period. For the coastal region of Bangladesh, daily accumulated rainfall of 44 mm/day is considered the threshold for heavy rainfall [68]. Accordingly, rainfall events meeting or exceeding this threshold were selected for inundation analysis. Figure 8 illustrates the corresponding  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Metric** & **RF** & **KNN** & **SVM** \\ \hline _t_-test _p_-value & 0.0022 * & 0.0036 * & 0.0005 * \\ \hline [PERSON]’s _p_-value & 0.0020 * & 0.0026 * & 0.0016 * \\ \hline \hline \end{tabular}
* indicates statistically significant (_p_ < 0.05).  
\end{table}
Table 2: Statistical comparison of classification models using paired _t_-test and [PERSON]’s test for RF, SVM, and KNN.  
Figure 6: _ROC_ curves for threshold 1.025 for RF, SVM, and KNN models.  
spatial inundation patterns during these events. On 24 July 2017, a peak monsoon rainfall event, with an aerial-averaged rainfall of 110 mm/day, led to extensive inundation across Bagerhat and surrounding areas. In contrast, the eastern coastal region experienced less flooding, with notable inundation limited to areas around Noakhali and Maheshkhali (Cox's Bazar district) (Figure 8a). The total inundated area was approximately 9639 sq. km. On 10 June 2018, another heavy rainfall event of 132 mm/day caused flooding over 8264 sq. km, primarily affecting the south-central coast, with significant inundation observed in the Pirojpur and Kalapara regions (Figure 8b). The 2019 monsoon season brought relatively light rainfall of 40 mm/day, resulting in a reduced inundated area of 3461 sq. km. Moderate flooding was recorded in parts of the western coast, particularly near Morrelganj and Kaliganj (Figure 8c). In 2020, rainfall reached 110 mm/day, leading to an inundation area of 5396 sq. km, with major impacts near Morrelganj and Amatali (Barguna district), while the rest of the coast experienced minimal flooding (Figure 8d). During the 2021 monsoon, rainfall of 98 mm/day led to a larger inundation area of 7723 sq. km, with Mongla (Bagerhat district) and its surrounding regions being most affected. Additional flooding was observed in the eastern coastal zones, particularly near Feni and Chakaria (Figure 8e). On 9 June 2022, a relatively low rainfall event of 50 mm/day still caused significant inundation in Paikgachha (Khulna district) and Morrelganj, though the rest of the coastal region experienced limited flooding. The total inundated area was 4307 sq. km (Figure 8f). The 2023 monsoon, on 7 August, brought 90 mm/day of rainfall, resulting in widespread inundation over 10,333 sq. km. The central coast near Rajapur (Jhalokati district) and Hatiya Island (Noakhali district) were the most impacted, while areas like Feni saw relatively less flooding (Figure 8g). On 1 August 2024, another major monsoon event with 110 mm/day of rainfall caused an inundation extent of 9888 sq. km. Morrelganj, Noakhali, and Hatiya Island were heavily affected, alongside some parts of the central coast (Figure 8h).  
Figure 7: The area-averaged daily accumulated rainfall from 2017 to 2024.