A simple water balance model for the simulation of streamflow over a large geographic domain

This article describes the development, application and validation of a macro-scale hydrological model, designed to simulate streamflow from climatic inputs over a large geographic domain. The model is a daily water balance model, which assumes that the soil moisture storage capacity varies statistically across the catchment: all other catchment properties, and climatic inputs, are assumed constant across the catchment. Model parameters are derived, directly or indirectly, from digital spatial data bases. The model is currently implemented at a spatial resolution of 0.5 x 0.5 degrees (approximately 2000 km(2)), because that is the resolution of the currently available climatic input data. In fact, the article emphasises how the form, parameterisation and quality of simulated output are strongly determined by the quality and characteristics of the data used both to define model parameters and to run the model. The article illustrates the model tuning process-which includes assessment of the input data-using the example of an application in Europe. (C) 1999 Elsevier Science B.V. All rights reserved.