The interaction of topographic slope with various geo-environmental flood-causing factors on flood prediction and susceptibility mapping.

This work integrates topographic slope with other geo-environmental flood-causing factors in order to improve the accuracy of flood prediction and susceptibility mapping using logistic regression (LR) model. The work was done for the eastern Jeddah watersheds in Saudi Arabia, where flash floods constitute a danger. A geospatial dataset with 140 historical flood records and twelve geo-environmental flood-causing factors was constructed. A number of significant statistical methods were also applied to provide reliable flood prediction and susceptibility mapping, including Jarque-Bera, Pearson's correlation, multicollinearity, heteroscedasticity, and heterogeneity analyses. The results of the models are validated using the area under curve (AUC) and other seven statistical measures. These statistical measures include accuracy (ACC), sensitivity (SST), specificity (SPF), negative predictive value (NPV), positive predictive value (PPV), root-mean-square error (RMSE), and Cohn's Kappa (K). Results showed that both in training and testing datasets, the LR model with the slope as a moderating variable (LR-SMV) outperformed the classical LR model. For both models (LR and LR-SMV), the adjusted R2 is 88.9 and 89.2%, respectively. The majority of the flood-causing factors in the LR-SMV model had lower Sig. R values than in the LR model. As compared to the LR model, the LR-SMV attained the highest values of PPV (90%), NPV (93%), SST (92%), SPF (90%), ACC (89%), and K (81%), for both training and testing data. Moreover, employing slope as a moderating variable demonstrated its viability and reliability for defining precisely flood-susceptibility zones in order to reduce flood risks.