development and application of the qausi distributed water balance model (qdwb) in the neishaboor-rokh watershed

limitation of water resources in iran motivates sustaining and preserving of the resources in order to supply future water needs. fulfilling these objectives will not be possible unless having accurate water balance of watersheds. the purpose of this study is to estimate the water balance parameters using a distributed method. the large number of distributed models and methods was studied and “quasi distributed water balance model” (qdwb) was written in the matlab programming environment. to conduct this model, it is needed that each data layer (precipitation, potential evapotranspiration, land use, soil data,..) to be converted into grid format. in this research the 500m * 500m cell size was used and water balance parameters for each cell was estimated. runoff and deep percolation obtained from surface balance equation and irrigation needs were estimated based on soil moisture deficit. the study area of 9157 square kilometers is neyshabour- rokh watershed. the results showed there is a good correlation between water balance parameters such as precipitation-runoff, precipitation-evapotranspiration, and precipitation- deep percoulation and demonstrate that qdwb model is consistent with the basin hydrological process.change in soil moisture at basin wide is 1 mcm in 1388-89 and 40 mcm in 1380-81. the evapotranspiration results from a distributed model” swat” and qdwb model were in good agreement.