Abstract

Flash floods are the most dangerous type of natural disasters in arid regions, such as Saudi Arabia. The effects of urban growth, witnessed between 1990 and 2010, in Makkah city, Saudi Arabia, on runoff volume and peak discharge are investigated using the curve number (CN) flood-modelling methodology. Shapefiles of residential areas are compiled and integrated in a unique geographic information system (GIS) environment. Datasets of geological structures, soil types, and a digital elevation model (DEM) have been collected and utilized. Peak discharges have been computed on the wadi scale, while the total flood volume have been estimated on the sub-basin scale for residential sub-basins in order to get a detailed view of urbanization impacts on flood hazards. The results obtained show that the residential regions of Makkah city have been increased, over the period 1990 to 2010, by 197%, while the total flood volumes have been enlarged by 248%. The spatial distribution of high-flood urban regions is mapped. Furthermore, the results show significant positive correlations between urbanization and both peak discharge and flood volume. Accordingly, these findings should be taken into account in future urbanization, sustainable development and flood management plans of Makkah metropolitan area.

Key words: Flood hazards, rainfall-runoff, curve number (CN), geographic information system (GIS), Saudi Arabia.