The sensitivity of thermally driven mountain flows to land cover change

The influence of heterogeneous land cover on the boundary layer and surface conditions was examined in the mountainous, semiarid Wasatch Front region of northern Utah using the Pennsylvania State University/National Center for Atmospheric Research fifth generation Mesoscale Model (MM5). In addition, model sensitivity studies were conducted to evaluate the effect of land cover change on surface temperatures and on the depth of the convective boundary layer. The Great Salt Lake and Utah Lake were found to play dominant roles in modulating the depth of the convective boundary layer, and areas of urban and agricultural land cover exerted local effects. Subsidence arising from slope flows and a cross-valley circulation were not found to have a large impact on the boundary layer in this case.; A model run was conducted in which all anthropogenic land cover types (e.g., urban, residential, agricultural) in the initial simulation, termed the 1992 run, were changed to grassland, to simulate the conditions that existed prior to large-scale human habitation. This was termed the 1847 run, as the valleys of the Wasatch Front were largely grassland prior to 1847. Compared to the 1847 run, the convective boundary layer in the 1992 run was deeper over urban land and shallower over irrigated cropland. In addition, the lake breeze front was faster to arrive in the urbanized area of the Salt Lake Valley but slower to move past the urban core. This was a result of the convergent circulation over the locally warm urban area. It is hypothesized that as urban land increasingly replaces agricultural land in semiarid regions, local temperature and convective boundary layer depth anomalies, as well as nonlocal effects on the lake breeze, will have more dramatic effects than the urbanization of natural land cover.