A regional maximum likelihood approach for calibrating rainfall-runoff models in ungauged basins

Parameter estimation for rainfall-runoff models in ungauged basins is a challenging task that is receiving significant attention. In fact, many practical applications suffer from problems induced by data scarcity, given that hydrological observations are often sparse or unavailable. The maximum likelihood function in the spectral domain proposed by Whittle (1953) is approximated in the time domain by maximising the fit of selected statistics of the river flow process, with the aim to propose a calibration procedure that can be applied at regional scale. Accordingly, the statistics above are related to the dominant climate and catchment characteristics, through regional regression relationships. The proposed technique is applied to the case study of 4 catchments located in central Italy, which are treated as ungauged. The outcomes of the analysis confirm the potential of the proposed methodology, that may be applied to any type of rainfall-runoff model.