Curve-Number/Green-Ampt mixed procedure for streamflow predictions in ungauged basins: Parameter sensitivity analysis.

A procedure combining the Soil Conservation Service - Curve Number (SCS-CN) method and the Green-Ampt (GA) infiltration equation was recently developed to overcome some of the drawbacks of the classic SCS-CN approach when estimating the volume of surface runoff at a sub-daily time resolution. The rationale of this mixed procedure, named CN4GA (Curve Number for Green Ampt), is to use the GA infiltration model to distribute the total volume of the net hyetograph (rainfall excess) provided by the SCS-CN method over time. The initial abstraction and the total volume of rainfall given by the SCS-CN method are used to identify the ponding time and to quantify the hydraulic conductivity parameter of the GA equation. In this paper, a sensitivity analysis of the mixed CN4GA parameters is presented with the aim to identify conditions where the mixed procedure can be effectively used within the Prediction in Ungauged Basin (PUB) perspective. The effects exerted by changes in selected input parameters on the outputs is evaluated using rectangular and triangular synthetic hyetographs as well as 100 maximum annual storms selected from synthetic rainfall time series. When applied to extreme precipitation events, which are characterized by predominant peaks of rainfall, the CN4GA appears to be rather insensitive to the input hydraulic parameters of the soil, which is an interesting feature of the CN4GA approach and makes it an ideal candidate for the rainfall excess estimation at sub-daily temporal resolution at ungauged sites.