Improving predictions of daily hydrologic response for ungauged catchments by incorporating water yield predictions on an inter-annual timestep

In order to model fluxes of water from the land surface to the atmosphere, and from one grid cell to another inclimate models, predictions of hydrologic response are required for catchments where hydrologic data are not available.A methodology has been presented previously that has the capability of producing estimates of catchment scale hydrologicresponse on a daily timestep (Post and Jakeman, 1997). In the present paper, it is demonstrated that these daily predictionsof hydrologic response can be improved by incorporating information about the hydrologic response of the catchment ona longer timestep. This is because the influence of large scale phenomena such as climate and vegetation may produce asimilar water yield in adjacent catchments, even though their daily hydrologic response may be different, due to differencesin drainage density for example. As a result, the water yield of an ungauged catchment can be inferred on an inter-annualtimestep, and this information used to balance the water budget of a daily timestep rainfall-runoff model. It was found thatusing tree stocking densities to predict water yields over a 4 year period for small experimental catchments in the Maroondahregion of Victoria produced better results than those obtained by inferring the water balance parameter of a daily timesteprainfall-runoff model from channel gradient and catchment elongation. Good predictions of inter-annual water yield werealso obtained for small experimental catchments in the H. J. Andrews, Hubbard Brook, and Coweeta long term ecologicalresearch (LTER) sites in the United States, indicating that this technique may be used to produce high quality predictionsof daily hydrologic response for ungauged catchments in these regions.