Continuous daily hydrograph simulation using duration curves of a precipitation index

The paper describes a parsimonious approach for generating continuous daily stream-flow time-series from observed daily rainfall data in a catchment. The key characteristic in the method is a duration curve. It is used to con vert the daily rainfall information from source rain gauges into a continuo us daily hydrograph at the destination river site. For each source rain gau ge a time-series of rainfall related 'current precipitation index' is gener ated and its duration curve is established. The current precipitation index reflects the current catchment wetness and is defined as a continuous func tion of precipitation, which accumulates on rainy days and exponentially de cays during the periods of no rainfall. The process of rainfall-to-runoff c onversion is based on the assumption that daily current precipitation index values at rainfall site(s) in a catchment and the destination site's daily flows correspond to similar probabilities on their respective duration cur ves. The method is tested in several small catchments in South Africa. The method is designed primarily for application at ungauged sites in data-poor regions where the use of more complex and information consuming techniques of data generation may not be justified. Copyright (C) 2000 John Wiley & S ons, Ltd.