Effects of land-cover change on rainfall-runoff relationships: A case study of the Yarkon-Ayalon watershed, Israel

Temporal changes and spatial patterns are often studied by analyzing land-cover changes (LCCs) using spaceborne images. LCC is an important factor, affecting runoff regime within watersheds through processes such as urbanization, agricultural activities, quarries and afforestation. The objective of this research was to estimate the effects of 20 years of LCCs on rainfall-runoff relations in an extreme rainfall event, in a sub-basin scale. A Landsat TM-derived classification map was used as an input for the Kinematic Runoff and Erosion (KINEROS2) hydrological model along with precipitation data of an extreme rainfall event. Model calibration was performed by using total runoff volume data based on hydrometric measurements taken during this rainfall event. Validation of the model performance was conducted by comparing the model results to measured data in order to receive output accuracy estimation. A similar procedure was then used with a 2009 land-cover classification map, derived from a Landsat TM image, as an input to KINEROS2 model, along with the same precipitation data and calibration parameters, in order to understand the possible outcomes of a rainfall event of such magnitude and duration after 20 years of LCCs. The results show a slight increase in runoff volume and peak discharge values between the examined time periods as a result of LCCs. In addition, a strong relationship was spotted between vegetation cover along the six sub-basins and the runoff volume. The LCCs that had the most pronounced effects on runoff volumes were related to urbanization and vegetation removal.