# The Sensitivity Analysis of Parameters in the 1D-2D Coupled Model for Urban Flooding
## 4 Results and Analysis  
### Local Sensitivity Analysis  
By analyzing the sensitivity of the Morris method parameters under different rainfall patterns (cxzd50a, szzbl50a, and Chicago50a), positive values indicate that an increase in the value of the parameter has a positive effect on water volume, and negative values have the opposite effect, as shown in Figure 4a. Minimum infiltration rate (Minrate) showed the most significant negative effect in all three rainfall patterns, with sensitivity coefficients of \(-0.537\) (cxzd50a), \(-0.131\) (szzbl50a), and \(-0.448\) (Chicago50a), indicating that increasing this parameter significantly reduced the water volume. Pipe roughness (Roughness) showed a positive correlation in all three rainfall patterns, and its sensitivity coefficient was very close to \(0.396\) and \(0.395\) for the cxzd50a and Chicago50a rainfall patterns, respectively, while it was \(0.270\) for the szzbl50a rainfall pattern, indicating that higher roughness increases the water volume.  
The sensitivity coefficients for Manning's coefficient of pervious surface area (N-Perv) also showed a significant negative correlation, with the largest effect of \(-0.511\) under the szzbl50a rain pattern, and \(-0.141\) and \(-0.194\) under the cxzd50a and Chicago50a rain patterns, respectively. Surface roughness (friction) also had a large effect on water volume, with sensitivity coefficients for all three rain patterns, especially the highest sensitivity coefficient of \(0.316\) under the Chicago50a rain pattern, indicating that an increase in surface roughness leads to more water accumulation. The velocity diffusion coefficient (Vd) showed a positive correlation in all three rainfall patterns, with sensitivity coefficients ranging from \(0.155\) to \(0.185\), indicating that this parameter also has a significant effect on water volume.  
Other parameters, such as decay coefficient (Dc), maximum infiltration rate (Maxrate), and ponding storage in the permeable zone (S-Perv), had relatively little effect on water volume. The sensitivity coefficient of decay time was \(0.174\) for cxzd50a and \(0.048\) and \(0.026\) for szzbl50a and Chicago50A, respectively. The sensitivity coefficient of maximum infiltration rate was negative for all three rainfall patterns, but the values were small, indicating that it had some effect on water volume reduction. The sensitivity coefficient of permeable area ponded storage is larger at \(-0.056\) under the szzbl50a rainfall pattern, while the effect is smaller under the other two rainfall patterns.  
Figure 4: Morris method sensitivity analysis. (**a**) Sensitivity \(\mu_{i}\) of different parameters; (**b**) Sensitivity strength ranking \(\mu_{i}^{*}\) of different parameters.  
Impervious area puddle storage (S-Imperv), stable infiltration rate (Fc), and Courant number (CFL) are less sensitive to water volume, and the sensitivity coefficients of these parameters are close to zero for all three rainfall patterns, indicating that they have a negligible effect on water volume. The order of sensitivity of different parameters is shown in Figure 4b.