This work is directed to assist decision makers to advance towards achieving proper management for surface water in a semi arid region. In this work a hydrological modeling was performed for surface water system in Zarqa river basin in Jordan. Under the umbrella of GIS, two models were used to simulate the water budget components of Zarqa watershed. Namely, hydrological Simulation Program - FORTRAN (HSPF) and the Soil and Water Assessment Tool (SWAT). Different unique scenarios were investigated by this work. Namely, climatic change scenarios, land use change scenarios, and water harvesting scenarios.