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 anyhydrological study on an ungauged basin, a methodology has to be appropriately selected for thedetermination of runoff at its outlet. Several methods have been used to estimate the basin runoffproduction. 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, meanslope and vegetation cover. A comparison between observed and calculated RC showed that a calibration ofthe Kennessey model could be necessary. The slight and not satisfying improvement of the calibrated modelsuggested that the main factors accounted for the Kennessey method could not be enough to describe meanrunoff production. So the analysis has been focused on researching empirical relations between RC andother variables which could play a significant role on RC estimation. Finally, the best result on RC estimatewas obtained by a simple linear regression for two Sicilian sub-zones, by considering only two mainclimatic parameters, average annual rainfall depth and average annual temperature.