What specific component of a flood hydrograph is most directly derived from the rainfall excess calculated using the Soil Conservation Service (SCS) Curve Number method?

The specific component of a flood hydrograph that is most directly derived from the rainfall excess calculated using the Soil Conservation Service (SCS) Curve Number method is the direct runoff portion. A flood hydrograph is a graphical representation illustrating the discharge, or flow rate, of water in a stream or river over time at a specific point, typically in response to a rainfall event. It is composed of two primary elements: baseflow and direct runoff. Baseflow represents the sustained flow primarily originating from groundwater discharge, occurring both before and after the immediate impact of a storm. Rainfall excess, also termed effective rainfall, is the fraction of total rainfall that remains after all losses have been subtracted, including initial abstractions like interception by vegetation and depression storage on the surface, as well as subsequent infiltration into the soil. This excess rainfall is the water that eventually becomes surface runoff and flows into stream channels. The SCS Curve Number method is an empirical hydrological model developed to estimate this cumulative rainfall excess for a specific storm, considering factors such as the watershed's soil type, land use or cover, and antecedent moisture conditions. It provides a quantitative value for the amount of rainfall that will transform into runoff. Consequently, the rainfall excess determined by the SCS Curve Number method directly dictates the volume of water that will form the direct runoff component of the flood hydrograph. This direct runoff constitutes the immediate, storm-generated increase in streamflow that overlays the baseflow, thereby forming the rising limb, the peak flow, and the initial part of the recession limb of the flood hydrograph, representing the water that quickly travels over the land surface and through shallow subsurface routes to the stream.