الفهرس 
ABSTRACT
General BackgroundOnly 14 pages are availabe for public view
 |  | from | 201 |  |  |
| | | from | 201 | | |
Abstract
A hydrological model is the mathematical representation of the flow of water and its constituents on the land surface or subsurface environments. the development of models has gone hand- in-hand with developments in computing power. Nowadays computer based hydrological models are indispensable tools in research and operational practice , and they are used for a variety of purposes , ranging from the prediction of runoff , flash flood and transmission losses to water quality and water resource studies .these models try to represent the spatial and temporal distribution of water and soils by using simple mathematical equations. the relationship between models and data is fundamental to the modeling task.In spite of the critical importance of water in arid and semi-arid areas , Hydrological data have historically been sverely limited . the shortage of data and the lack of high quality observations as well as potentially discontinuous occurrence of flow in both space and time are important charcteristics of the ephemeral streams in arid regions, therefor , development powerful hydrological models is difficult.