## 4 Results and Discussion
### Evaluation of Network-Carrying Capacity  
When infiltration is inhibited, surface runoff typically flows directly into the pipe network as soon as precipitation reaches the ground. If the network's drainage capacity is exceeded, reverse surface flow increases, resulting in surface drainage issues and potential waterlogging. To further assess the campus drainage capacity, the number of overflow nodes and overloaded conduits were calculated for various return periods. The performance of the campus network under different rainfall scenarios, as well as rainfall-induced ponding, were quantitatively evaluated. The simulation results indicate that no node overflow occurred during a 1-year return period (\(P\) = 1 y). Thus, overflow nodes and overloaded conduits were further analyzed for return periods of 2, 5, 10, 20, and 50 years. Figure 6 illustrates the variation in the number of overflow nodes (\(N_{n}\)) and overloaded conduits (\(N_{p}\)) over the rainfall duration, while Table 7 provides network service statistics for various precipitation scenarios. Figure 5: Comparison of rainfall intensity and outlet runoff for different return periods. As shown in Table 7 and Figure 6, for a given return period, the number of overflow nodes (\(N_{n}\)) and overloaded conduits (\(N_{p}\)) initially increased with rising rainfall duration and intensity, and then decreased, corresponding to fluctuations in the rainfall intensity. For return periods of 2, 5, 10, and 20 years, the maximum number of overflow nodes and overloaded conduits occurred at 45-60 min and 60-75 min, respectively. Across different precipitation scenarios, both overflow nodes and overloaded conduits increased as the scale of the storm intensified. Once the peak was reached, the network resumed function as the rainfall intensity declined, relieving overload and gradually restoring the network capacity. The drainage system became overloaded at a return period of 2 years, indicating limited resilience and generally poor performance in flood control and waterlogging prevention. For a substantial storm with a 10-year return period, 25.93% of the nodes overflowed, and 18.69% of the conduits were overloaded, with this condition persisting for 105 min. In a 20-year return period storm, 41.67% of nodes and 37.38% of conduits experienced overflow and overload, placing considerable pressure on the drainage network. During an extreme 50-year return period storm, 72.22% of nodes overflowed, and 57.94% of conduits were overloaded, resulting in severe ponding and widespread waterlogging. A clear upward trend was observed in the number of overflow nodes as the rainfall return period increased. When the return period rose from 2 years to 50 years, the number of overflow nodes increased significantly, from 6 to 73. The fraction of overflow nodes showed the smallest increase, rising from 5.56% to 12.96% (a change of 7.40%), between the 2-year and 5-year return periods. However, the fraction increased more substantially by 12.97%, 15.74%, and 30.55% between the 5-year and 10-year, 10-year and 20-year, and 20-year and 50-year return periods, respectively. For a 2-year return period (\(P=2\) y), the average durations of overflow nodes and overloaded conduits were 0.24 h and 0.21 h, respectively. In contrast, during a 50-year return period storm, the loading duration for a node or conduit within the campus network approached 1 h. These findings indicate