The impact of land use change on runoff generation in an urbanizing watershed in the north of Iran

Determining how land clearing and other land use changes will affect the amount of runoff is among the most important issues related to the watershed management. In this study, the L-THIA GIS model was applied to calculate the height and volume of runoff as well as the contribution of each land use type to producing runoff in a watershed under intense development pressure in the north of Iran. Different land use scenarios were also simulated using the CLUE-s model based on varying demands of each of the land use types. In this study, three different periods of 1986, 2000, and 2011 for the base period and 5 land use change scenarios for year 2030 were prepared. The results showed that the CLUE-s model is a suitable model to simulate future land use changes through the use of a ROC curve. The simulated runoff heights and runoff volumes were 132.55–165.31 mm and 119.295–148.779 m³/cell in base and future periods, respectively. The simulation of runoff under different land use scenarios showed that the amount of runoff in all the scenarios is more than the base period so that in a 44-year period (1986–2030) (assuming that the current rate of demand for land is constant), the total volume of runoff will increase by 54 % due to land use changes. The amount of runoff is also affected by the amount of land use demand, so that the amount of runoff reduces with the decrease in demand. The increased runoff, rise in urbanization as well as indiscriminate cutting of forests are the most important factors that contribute to increased runoff in the study area, and the development of new residential areas causes the most significant increases in runoff. This study has shown that the hydrologic effects of land use changes can be reduced with an exact physical design of area land use through controlling the demand of each land use.