Investigation of the effect of climate change on runoff curve number by using GIS and RS (case study: Mansourabad and Navroud watersheds)

  Application of gepraphic information system and image processing in evaluation of surface runoff of a watershed in recent years has increased greatly. In the study , the runoff curve number map was prepared using geographic information system (GIS)and Landsat Sattelite Images (ETM+)for two watersheds of Mansourabad in southern Khorasan province and Navroud in Gilan province based on the factors of hydrologic soil group, land use, land cover and hydrologic conditions. The land cover map was perpared by NDVI index and  watersheds were classified by three classes of good, fair and weak sitation vegetation in Mansourabad watershed but for Navrood watershed, Vegetation had three classes of excellent, good and moderate. Land use map of this watersheds  was prepared from Landsat Sattelite Images and Soil Hydrologic Group addition to soil, slope and Landuse, geology  maps plus filed investigations. From Coalition of GIS shape files and SCS tables, runoff curve number map was extrcated for both watersheds. In evaluation of  accuracy of Curve Number, maximum flood discharge in both two watersheds was simulated by HEC-HMS model  and compared with observed data. Low errorr discrepancy between simulated and observed dischrge showed that curve number for both basins was calculated with high accurcy. So results showed that weithing runoff curve number   in MansoorAbad basin is highly greater than Navrood basin, that this parameter can cause destructive floods  during hight intensity events.