Future predictions of the atmospheric circulation and regional hydroclimate in the Pacific-North American Sector.

A critical aspect of human-induced climate change is how it will affect regional hydroclimate around the world.  To leading order, the increased ability of the atmosphere to hold moisture as it warms, intensifies moisture transports, making sub-tropical dry regions drier and mid-latitude wet regions wetter.  But regional changes in hydroclimate will also depend on how the atmospheric circulation responds to warming.
Here, the predictions of the future of the circulation by the current generation of global climate models will be discussed, with a particular focus on circulation changes that impact on regional hydroclimate.  In the Pacific-North American Sector, during Northern Hemisphere winter, changes in the stationary waves are a leading order effect. The focus will be on two aspects of circulation change in this region.  The first is the predicted change in the meridional wind field over North America, which is closely linked to North American hydroclimate change.  The second is the predicted poleward shifting of the westerlies in the mid-latitude Pacific and its relation to tropical circulation change.  There is considerable diversity among the models in both these aspects of future circulation change, with important implications for regional hydroclimate predictions.