Estimation of regional parameters in a macro scale hydrological model - Paper presented at the Nordic Hydrological Conference (Uppsala, Sweden June, 2000)

Macro-scale hydrological modelling implies a repeated application of a mode l within an area using regional parameters. These parameters are based on c limate and landscape characteristics, and they are used to calculate the wa ter balance in ungauged areas. The regional parameters ought to be robust a nd not too dependent of the catchment and time period used for calibration. The ECOMAG model is applied for the NOPEX-region as a macro-scale hydrolog ical model distributed on a 2x2 km(2) grid. Each model element is assigned parameters according to soil and vegetation classes. A Bayesian methodology is followed. An objective function describing the fit between observed and simulated values is used to describe the likelihood of the parameters. Usi ng Baye's theorem these likelihoods are used to update the probability dist ributions of the parameters using additional data, being it either an addit ional year of streamflow or an additional streamflow station. Two sampling methods are used, regular sampling and Metropolis-Hastings sampling. The re sults show that regional parameters exist according to some predefined crit eria. The probability distribution of the parameters shows a decreasing var iance as data from new catchments are used for updating. A few parameters d o, however, not exhibit this property, and they are therefore not suitable in a regional context.