Implications of global climate change over mountain areas of western North America

The substantial terrain of the western U.S. plays a crucial role in determining the climate and weather regimes of the region, but is poorly resolved by general circulation models used in most global warming studies. To address this deficiency, both MM5 and WRF mesoscale models have been run at high resolution (12-km grid spacing) over the Northwest U.S. and at moderate resolution (36-km grid spacing) over western North America for a range of decadal periods (1990-2000, 2025-2035, 2045-2055, 2090-2100). The results demonstrate the profound effects of terrain on the local implications of global warming. It is shown that the inability of general circulation models to properly resolve the Rocky Mountains result in unphysical cold waves extending to the West Coast. Furthermore, climate change results in bands of warming along major regional terrain as rising snow level produces zones of enhanced absorption of solar radiation by newly bared soil. Increased heating in the interior of the continent results in enhanced onshore pressure gradients and upslope clouds on windward slopes. These and other regional changes produced by the interaction of western terrain and large-scale circulation changes under global warming will be discussed in this presentation.