## 4 Discussion  
### The Scenario-Based Flood Risk Analysis Framework  
Given the projected risk fluctuation and more potential extreme rainfall events in the PLEEZ, substantial uncertainty will likely feature future flood risk management, prompting the need for developing a robust response strategy for optimizing the current decision-making process. Here, our proposed scenario-based flood risk analysis framework, which considers flood inundation-prone and high-risk zones, assesses risk from multiple perspectives rather than from the single perspective of risk maps as in previous methods (Figure 12). According to this framework, first, the flood high-risk zone (Figure 12a) is composed of the very high and high-risk areas in the baseline map. Second, the flood inundation-prone zone (Figure 12b) is extracted from the hot spots of historical flood inundation frequency in Figure 6b (detailed procedure in the Supplementary Materials). After spatially overlaying these two zones, three types of response ranks with distinct risk characteristics are obtained. As described in Section 2.3.1, the red intersecting part (Figure 12c) corresponds to Rank 1 (high-risk and inundation-prone; Figure 12d), and the non-intersecting portions represent \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Scenario**} & \multirow{2}{*}{**Period**} & \multicolumn{2}{c}{**Areas Converted from Unused Lands**} & \multirow{2}{*}{**Total Areas of Significant**} & \multirow{2}{*}{**Ratio (\%)**} \\  & & **Such as Wetland and Bare Land to** & & **Increase (km\({}^{2}\))** & \\ \hline \multirow{3}{*}{SSP2-RCP4.5} & 2030s & 52 & 64 & 81.25\% \\  & 2040s & 51 & 69 & 73.91\% \\  & 2050s & 33 & 44 & 75.00\% \\ \hline \multirow{3}{*}{SSP5-RCP8.5} & 2030s & 78 & 118 & 66.10\% \\  & 2040s & 54 & 77 & 70.13\% \\ \cline{1-1}  & 2050s & 45 & 69 & 65.22\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Main land use type changes in areas with significant increases in risk in the PLEEZ. Figure 12: An illustration of the flood risk analysis framework combining the flood inundation-prone zone and high-risk zone. two additional assessment perspectives: Rank 2 (high-risk but non-inundation-prone; Figure 12e) and Rank 3 (non-high-risk but inundation-prone; Figure 12f). For Rank 1 areas (2526 km2), inundation is more likely to occur and cause great damage; thus, these areas require priority governance and more proactive consideration by policy-makers. Considering the proximity of wetland and bare land along the lake in this rank, through policy regulation, the land-use structure should be further improved to preserve the wetland ecosystems, including reconverting cropland into wetland and grassland, because inappropriate land-use changes in wetland resources would bring a dramatic increase in risk, as revealed in Section 3.2.2 for our case study. For urban areas along rivers, resilience against floods could be enhanced by strengthening the drainage network's discharge capacity, increasing emergency storage facilities and planning infrastructure development beyond the flood return period. Rank 2 (3395 km2) characterizes a potential flood threat that cannot be ignored in the future. Given the uncertainty of extreme rainfall caused by climate change, Rank 2 areas may evolve into Rank 1 areas, so adaptive mitigation measures should be taken in advance. In this context, sponge cities represent a green and sustainable solution. This approach entails a systematic project that reduces flood flows by improving the infiltration, absorption and collection of water from the excessive, impervious underlying surfaces derived from rapid urbanization. For Rank 3 areas (3238 km2), although flood losses are currently minor, once flooding is out of control, danger rapidly spreads to the surrounding areas or middle and lower reaches of the local rivers (i.e., aggravating disaster in Rank 1 and Rank 2 areas), as most of Rank 3 areas are located along rivers. Therefore, real-time flood monitoring and forecasting during the flood season are key measures for these areas.