Uncertainty in hydrological modelling of climate change impacts in four Norwegian catchments

Projections for the hydrological impacts of climate change are necessarily reliant on a chain of models for which numerous alternative models and approaches are available. Many of these alternatives produce dissimilar results which can undermine their use in practical applications due to these differences. A methodology for developing climate change impact projections and for representing the range of model outcomes is demonstrated based on the application of a hydrological model with input data from six regional climate scenarios, which have been further adjusted to match local conditions. Multiple best-fit hydrological model parameter sets are also used so that hydrological parameter uncertainty is included in the analysis. The methodology is applied to consider projected changes in the average annual maximum daily mean runoff in four catchments (Flaksvatn, Viksvatn, Masi and Nybergsund) which are characterised by regional differences in seasonal flow regimes. For catchments where rainfall makes the predominant contribution to annual maximum flows, hydrological parameter uncertainty is significant relative to other uncertainty sources. Parameter uncertainty is less important in catchments where spring snowmelt dominates the generation of maximum flows. In this case, differences between climate scenarios and methods for adjusting climate model output to local conditions dominate uncertainty.