Cooperative Institute for Research in Environmental Sciences

Predicted Changes in Synoptic Forcing of Net Precipitation in Large Arctic River Basins During the 21st Century

Daily output from fifteen global climate system models and two global reanalyses were analyzed to create a synoptic climatology of Arctic sea level pressure and to assess predicted changes in net precipitation over the Arctic. The method of self-organizing maps was used to create the synoptic climatology from three decades of model output; 1991-2000, 2046-2055, and 2091-2100. The model derived synoptic climatology was compared to that from the two reanalyses, for the period 1991-2000, and this comparison was used to select a subset of models which best reproduced the currently observed synoptic climate of the Arctic. Of the fifteen models evaluated in this way only 4 models were able to reproduce the key features of the Arctic synoptic climate as depicted by the two global reanalyses. The synoptic climatology created using the self-organizing map technique lends itself to the study of extreme events and the projections from this subset of 4 models indicate an increase in cyclonically dominated weather patterns over the 21st century. The models also projected an increase in net precipitation over the Arctic cap and the large Arctic river watersheds during the 21st century. Using the synoptic climatology, a method to assess thermodynamic and circulation related changes in net precipitation was derived. The results of this assessment indicate that thermodynamic changes are responsible for more than 75% of the predicted change in Arctic net precipitation during the 21st century.