Incorporating natural variability in master recession curves

In this paper we hypothesise that there is a continuum of recession curves that can be represented by a single (average) Master Recession Curve (MRC) or by a family of percentile curves. The continuum of MRCs represents the natural variability, which is the aleatory uncertainty across the continuum, and is the result of variability in antecedent hydroclimatic and heterogeneous storage conditions in unconfined aquifer/s supplying streamflow. For four streams spanning the range of Australian hydrology, master recession curves were computed for antecedent conditions with exceedance percentiles ranging from 10 % to 90 % using the correlation technique. Observed recessions were superimposed on the plots confirming that the continuum of MRCs represented the observed variability in antecedent conditions. For one catchment, the Northern Arthur River (437 km 2 in Western Australia yielding 2.7 mm runoff per year), field data were available. These were used to develop a two-store qualitative model that supports the continuum concept.