effects of land use changes on flood characteristics using hec-hms model (case study: taleghan watershed)

land use change is one of the main factors in the process of changing the regime of flood in watersheds. taleghan watershed has been subjected to many land use changes over years, which probably effects on flood characteristics of taleghan river. in present study the effects of land use change on some parameters including peak flow, volume and flood base time, in part of taleghan basin, was investigated by using geographical information system (gis) and hec-hms model. land use maps of 1987 and 2002 were prepared and integrated with soil hydrological groups and pasture conditions maps in gis with the aim of providing of cn map. then by using curve number and scs unit hydrograph in sub basins and also muskingum routing method,  hec-hms model was calibrated and validated, for 10 incident rainfall - runoff views. results of the simulation showed that due to the changes in land use (the reduction in the level of agricultural lands and increases in pasture areas), peak flow and flood volume in 2002 than in 1987 showed the average reduction of 46% and 34%, respectively. the evaluation of base time of flood showed no change in the parameter in flood hydrograph at the study period. on the whole the results showed that the trend of land use changes have the positive effect on reducing flood productions in study area.