Most of Saudi Arabia can be considered a typically arid region where the annual average amount of rainfall varies between 50 and 100 mm. Asser Region in western Saudi Arabia is characterized by high rainfall intensity that leads to flash floods. Using digital elevation model (DEM) Watershed and its stream were delineated and morphological parameters calculated using Watershed Modeling System (WMS). Rainfall frequency analysis was performed for selected three rainfall gages using annual maximums of 24-h rainfall. As a result of the sparse hydrologic information, the relation between rainfall and runoff was calculated depending on the morphometric parameters, GIS techniques, Watershed Modeling System (WMS) and Hydrologic Engineering Center- Hydrologic Modeling System software (HEC HMS). In this work, the flood risks were studied and the results are considered the baseline data required to designate the required protection system against these risks. This study aims to assess the impact of flash floods in the Wadi Reem basin, which located in Assir Region, Saudi Arabia