LAUSR

Abstract The present study evaluates the performance of five existing and three proposed antecedent moisture condition (AMC)-based runoff curve number (CN) conversion formulae utilizing the data of a large number of naturally observed rainfall (P)–runoff (Q) for an agricultural field located at Roorkee, Uttarakhand, India and available published data around the globe. For developing the proposed formulae, CNs were derived for P–Q datasets from 39 watersheds using standard initial abstraction ratio (λ) values as 0.20 and 0.030. The existing formulae outperformed the proposed formulae when tested numerically using the available National Engineering Handbook chapter–4 (NEH–4) tabular AMC-dependent CNs as target values. It might be because the existing formulae were derived from the same datasets used as targeted values (i.e. NEH–4 AMC defining tables). Therefore, when tested on large set of field data, the three proposed formulae performed better than the existing ones, the formula with λ = 0.030 the best of all.