Impact of anthropogenic land-use/land-cover change on climate and hydrologic cycle over the Greater Phoenix Area.

The impact of land-use/land-cover (LULC) change over the Greater Phoenix (AZ) area is investigated through use of the Regional Atmospheric Modeling System (RAMS). A single grid simulation, using a grid cell spacing of 50-km and a domain covering the entire U.S., is used to conduct a month-long simulation for May 1995. The results from this simulation were validated against gridded data and subsequently used as lateral boundary conditions for a nested grid configuration centered over the Greater Phoenix area. The outer grid in this ensuing two-grid configuration is initialized and forced by LBCs resulting from the single grid monthly simulation and is integrated for one month: June 1995. Three different ensemble members were initialized using the resulting simulated soil moisture/temperature, from the set-up above, where the difference between members consisted of three different starting dates. Each ensemble member implements a second nested grid (Grid 3), and the three-grid configuration (with the fine grid using a 2-km grid cell spacing) is integrated for the entire month. This set-up serves as a configuration for two general types of simulations: one ensemble using a natural shrubland/desert land cover, representing pre-urban native vegetation, and another ensemble using 1992 LULC data derived from 1990's Landsat data. Differences in total rainfall, frequency and intensity of individual events, are linked to changes in the underlying dynamic and thermodynamic processes, investigated through analysis of the vertical profiles of winds, temperature, and moisture, along with various indices of stability, convective potential, and cloud development. We find that simulation of event-scale to seasonal precipitation in the Greater Phoenix area during the wettest part of the year, that of the North American Monsoon System (NAMS), is sensitive to these land-surface changes.