 The soil conservation service curve number, SCSCN, approach is commonly used to predict direct runoff volume for a given rainfall event, but it can be improved by estimating the CN value from measured rainfall runoff data instead of using table values. However, previous research has shown that calculated CN values vary with rainfall depth, and a single asymptotic CN value observed at very high rainfall depths may not accurately characterize a watershed's runoff response. In this paper, the hypothesis that soils and land cover spatial variability effect a watershed's hydrologic response is tested by introducing a simplified 2CN heterogeneous system to model CN rainfall variation. The results indicate that the proposed method provides reasonable accuracy and outperforms previous methods based on determining a single asymptotic CN value, although it increases the number of unknown parameters to three. This article was authored by J. D. Valianzis and K. X. Suleys.