The Influence of Urbanization on the Climate of the Las Vegas Metropolitan Area: A Numerical Study

In this study, the Weather Research and Forecasting (WRF) Model and its embedded land surface and urban canopy model are used to simulate effects of urbanization on the local climate of the Las Vegas, Nevada, metropolitan area. High-resolution simulations are performed with a 3-km horizontal resolution over the city. With identical lateral boundary conditions, three land use/land cover (LULC) maps for 2006, 1992, and hypothetical 1900 are used in multiple simulations. The differences in the simulated climate among those cases are used to quantify the urban effect. The study found that urbanization in Las Vegas produces a classic urban heat island (UHI) at night but a minor cooling trend during the day. An analysis of the surface energy balance helps illustrate the major roles of the decreases in surface albedo of solar radiation and increases in the effective emissivity of longwave radiation in shaping the local climate change in Las Vegas. In addition, the emerging urban structures are found to have a mechanical effect of slowing down the climatological wind field over the urban area as a result of an increased effective surface roughness. The slowing down of the diurnal circulation leads to a secondary modification of temperature, which exhibits a complicated diurnal dependence. This suggests the need for more investigations into the coupling of thermodynamic and mechanical effects of urbanization on local climate.