Relationship between Curve Number and φ-Index

Nicholas S. Karpathy, David A. Chin

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


The curve number (CN) model was originally developed to estimate the total runoff resulting from a given rainfall event. However, the CN model has a limited ability to estimate realistic incremental rainfall excesses within rainfall events. This limitation is problematic because incremental rainfall excesses during a rainfall event are usually the input data required for calculating runoff hydrographs. In contrast to the CN model, the φ-index model provides more realistic estimates of incremental rainfall excesses during a rainfall event. This study investigated the relationship between the curve number and the φ-index at 10 different catchments in the United States. The results show that, for any given rainfall event, the φ-index can be directly related to the curve number, and there is a fair degree of consistency in the CN-φ relationship between catchments.

Original languageEnglish (US)
Article number06019009
JournalJournal of Irrigation and Drainage Engineering
Issue number11
StatePublished - Nov 1 2019
Externally publishedYes


  • Curve number
  • index
  • Infiltration
  • Rainfall
  • Runoff

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Water Science and Technology
  • Agricultural and Biological Sciences (miscellaneous)


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