Empirical determination of the average annual runoff coefficient in the Mediterranean area

Runoff estimation in ungauged basin is a challenge for the hydrological engineers and planners. For any hydrological study on an ungauged basin, a methodology has to be appropriately selected for the determination of runoff at its outlet. Several methods have been used to estimate the basin runoff production. In this study the empirical Kennessey method to determine average annual runoff coefficient, RC, is tested on 61 Sicilian basins characterized by different climate conditions, surface permeability, mean slope and vegetation cover. A comparison between observed and calculated RC showed that a calibration of the Kennessey model could be necessary. The slight and not satisfying improvement of the calibrated model suggested that the main factors accounted for the Kennessey method could not be enough to describe mean runoff production. So the analysis has been focused on researching empirical relations between RC and other variables which could play a significant role on RC estimation. Finally, the best result on RC estimate was obtained by a simple linear regression for two Sicilian sub-zones, by considering only two main climatic parameters, average annual rainfall depth and average annual temperature.