Numerical Simulations of Local Circulation and Its Response to Land Cover Changes over the Yellow Mountains of China

In this study, local circulations and their responses to land use and land cover (LULC) changes over the Yellow Mountains of China are examined by using Weather Research and Forecast (WRF) model simulations of a selected case under weak-gradient synoptic conditions. The results show that mountain-valley breezes over the region are characterized by an intense upslope flow lasting for about 11 h (0600-1700 LST) along the northern slope during daytime. A convergence zone occurs at the mountain ridge and moves northwest-ward with time. During nighttime, wind directions are reversed, starting first at higher elevations. Three sensitivity experiments are conducted, in which the current land covers are replaced by grassland, mixed forest, and bare soil, respectively, while keeping the other model conditions identical to a control run. These sensitivity simulations are designed to represent the changes of LULC over the Yellow Mountains area during the past decades. The results show that changes in land cover could affect substantially land-surface and atmosphere interactions, the evolution of local circulations, and characteristics of the planetary boundary layer (PBL). Significant differences are noted in horizontal winds, and sensible and latent heat fluxes. On the other hand, when the surface is covered by mixed forest, slight variations in local winds and surface variables are identified. The results appear to have important implications to urban planning and constructions as well as the transport of air pollutants over mountainous regions.