Curve Numbers Seasonal Variation in Mid-Mediterranean Area

AbstractThe curve number (CN) method is a popular technique for estimating a rainstorm event’s direct runoff (Q from its storm depth P). It relies on the parameter CN, a lumped expression of a watershed’s potential hydrologic response. Despite its widespread use over a variety of climates worldwide, the method’s primary documentation does not consider the influence of season on CN or runoff. Accordingly, CN analysis was done on 13 Sicilian basins, using rainfall-runoff data for multiday events from 1940 to 1997, with a mean record length of 32 years. Watershed CNs were determined from these data by the asymptotic fitting method and ordered data. These watersheds showed a standard asymptotic behavior with differences in asymptotically fitted CN (CN∞) between dry season and wet season. The found CNs were significantly higher (about 18 CNs) in the wet season (CNw) than in the dry season (CNd). However, the wet season CNs were not significantly different than the CNs for the pooled data, CNann. No statistically significant relationships among seasonal CNs and watersheds’ morphoclimatic and hydrologic characteristics were found, whereas the seasonal variation of watersheds’ CNs seems linked to the seasonality of rainfall.