This paper analyzes the effect of climate change and urbanization on the hydrological efficiency of dams that have been built to protect Jeddah city in Saudi Arabia from severe floods. Brayman Dam is considered a case study. Several data have been collected to address the objectives. Among these data are the historical rainfall, digital elevation models, a base map of Jeddah city, and its future expansion up to 2050. Hydrological analyses have been performed using common software: HEC-HMS, GIS, and WMS to estimate the floods under the current (design) condition, the effect of climate change, the effect of future urbanization and the combined effect of both. It has been shown that under the normal condition (NC) scenario, the Brayman dam capacity can accommodate the floods for up to 200 years return period. The effect of the climate change scenario (CC) is more significant than the effect of the urbanization scenario (U). The effect of urbanization scenario (U) leads to shortening the time to peak of the flood. In the combined scenarios (CC + U), the runoff volume exceeded the dam capacity by about 66%, the dam is expected to get overtopped by 26% from the current dam height, and the dam lake is expected to inundate 46% more area than the current condition.