Runoff modelling for snow-affected catchments in the Australian alpine region, eastern Victoria

Abstract A rainfall-runoff model is applied to two large catchments of the Murray-Darling Basin, Australia: the Kiewa (552 km 2 ) and Mitta-Mitta (1533 km 2 ) Rivers. These catchments are located in the highest parts of the Australian alpine region and the effects of snow melt-accumulation processes feature prominently in the hydrological regime of these rivers. Accordingly, a model is developed to compute equivalent rainfall from raw precipitation records, taking into consideration snow melt-accumulation processes in the different parts of these catchments. This model uses temperature and precipitation data as input, determined on a daily basis over the whole region under consideration (2085 km 2 ) using a spatial interpolation procedure with a resolution of 2.5 km × 2.5 km. The snow melt-accumulation model is based on a modified degree-day method and provides the equivalent amount of melted-accumulated water for each grid cell of the catchments considered. The method allows modelling of the melt-accumulation processes directly without requiring information about observed snow cover distribution in the area. Daily streamflow for the Kiewa and Mitta-Mitta Rivers is then modelled using as input the equivalent rainfall estimated by the snow melt-accumulation module and the mean daily temperature in each grid cell integrated over the whole catchments. Model calibration on 2 year periods is performed, and subsequent simulation of streamflow over an 18 year period of observation with these calibrated models yields encouraging results for those wishing to use such a simplified approach. Given scenarios of precipitation and temperature change, the model may be used to estimate future climate impacts under the assumption that the hydrological effect of vegetation cover in the area remains similar.