Beyond the SCS-CN method: A theoretical framework for spatially lumped rainfall-runoff response

M. S. Bartlett, A. J. Parolari, J. J. McDonnell, A. Porporato*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

64 Citations (Scopus)
14 Downloads (Pure)


Since its introduction in 1954, the Soil Conservation Service curve number (SCS-CN) method has become the standard tool, in practice, for estimating an event-based rainfall-runoff response. However, because of its empirical origins, the SCS-CN method is restricted to certain geographic regions and land use types. Moreover, it does not describe the spatial variability of runoff. To move beyond these limitations, we present a new theoretical framework for spatially lumped, event-based rainfall-runoff modeling. In this framework, we describe the spatially lumped runoff model as a point description of runoff that is upscaled to a watershed area based on probability distributions that are representative of watershed heterogeneities. The framework accommodates different runoff concepts and distributions of heterogeneities, and in doing so, it provides an implicit spatial description of runoff variability. Heterogeneity in storage capacity and soil moisture are the basis for upscaling a point runoff response and linking ecohydrological processes to runoff modeling. For the framework, we consider two different runoff responses for fractions of the watershed area: prethreshold and threshold-excess runoff. These occur before and after infiltration exceeds a storage capacity threshold. Our application of the framework results in a new model (called SCS-CNx) that extends the SCS-CN method with the prethreshold and threshold-excess runoff mechanisms and an implicit spatial description of runoff. We show proof of concept in four forested watersheds and further that the resulting model may better represent geographic regions and site types that previously have been beyond the scope of the traditional SCS-CN method.

Original languageEnglish
Pages (from-to)4608-4627
Number of pages20
JournalWater Resources Research
Issue number6
Early online date19 May 2016
Publication statusPublished - Jun 2016

Bibliographical note

This work was supported through the USDA Agricultural Research Service cooperative agreement 58-6408-3-027; and National Science Foundation (NSF) grants CBET-1033467, EAR-1331846, FESD-1338694, EAR-1316258, and the Duke WISeNet grant DGE-1068871. The data used for Figure 9 are reproduced from Tedela et al. [2011, 2008]. Processed data and code are available by e-mail from the corresponding author. We thank the reviewers for their useful and constructive comments that helped improve the paper.


  • SCS-CN method
  • soil moisture
  • event-based model
  • spatially lumped model
  • exponential rainfall
  • thresholds
  • curve number method
  • soil-moisture
  • hydrologic response
  • micro-topography
  • model
  • generation
  • catchment
  • variability
  • surface
  • flow


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