Assessment of impacts of land use changes on surface water using L-THIA model (case study: Zayandehrud river basin).

Land use changes in a basin are the most important factors affecting its hydrology and water quality. A hydrological model is an effective tool in assessing the effects of land use change on surface water. In this study, the effects of land use changes in the Zayandehrud basin are estimated using long-term hydrologic impact assessment model. This model is applicable using long-term data on climate, soil hydrological groups, and land use maps. The study covered three land uses across 18 years (from 1997 to 2015), and we used data on 30 years of precipitation (from 1985 to 2015) in the model. The results of modeling revealed that the average runoff volume increased from around 5,765,034 m3 in 1997 to 8,894,525 m3 in 2015. The results also showed an increase in runoff depth. Land use changes over the study period showed an increase of residential areas, bare land, and agricultural lands and a decrease of pasture and forests. The results can be used to make decisions and monitor changes in land use to control the depth and volume of runoff. Using output maps helps in delimitation of the areas that have high runoff average and in implementation of the management plans for controlling the amount of runoff in these areas. Appropriate land use design can decrease impacts of land use changes including hydrologic effects.