Synoptically forced hydroclimatology of major Arctic watersheds in general circulation models; Part 1: The Mackenzie River Basin

The ability of 14 general circulation models (GCMs) to realistically simulate weather patterns and precipitation regimes affecting the Mackenzie River Basin has been assessed. Applying the method of self-organizing maps to daily data from the model ensemble and the 40-year reanalysis project of the ECWMF (ERA-40), a regional synoptic climatology of sea level pressure was developed and used to analyse the model output. GCM performance, as compared with ERA-40, varies significantly between models and seasons, but is generally best during the summer and winter. In-depth examination of a five-model subset reveals biases in the placement of the Pacific storm track, which may be related to misrepresentations of the Beaufort High. Biases in Mackenzie Basin precipitation are only weakly connected to these circulation errors, and are, instead, primarily the result of inaccurate representations of basin-scale precipitation regimes. In particular, models allow excessive orographic precipitation along the west coast of North America to intrude into the Mackenzie Basin. These results suggest that projections of the Mackenzie's response to climate change could benefit from climate downscaling studies.