Land use changes in the Gharasoo watershed in Ardabil province were studied from 1987 to 2012 using the L-THIA model. The researchers found that these changes led to an average increase of 1.8 mm in runoff in the catchment area. The increase in residential areas and loss of woodland and pastures were the main factors contributing to this change. However, in some areas like Ardabil plain, converting pastures into farmland actually decreased runoff by increasing ground permeability. The model used was effective in showing the hydrological impacts of land use changes and identifying areas at risk of flooding in the watershed.