Remote Impacts of Lowland Urbanization on Orographic Cloud Properties

San Miguel de Tucuman, Argentina is a developing city located east (upwind) of the Andes Mountain range surrounded by open agricultural land. Orographic influences on regional climate have been extensively studied in prior research; however, the location of the urban development in San Miguel de Tucuman provides a unique opportunity to study the impacts of changing land use in a region upwind of topography. A process study was performed using control Weather Research and Forecasting (WRF) model run and a WRF run with the urban environment removed. Model results from the control run were compared with surface observations as well as satellite observations of cloud cover (MODIS, CloudSAT) and precipitation (TRMM). Significant differences between the two model simulations were observed particularly in cloud properties and precipitation patterns. These differences are attributed to altered vertical surface moisture exchange and atmospheric flow. Increased vertical mixing with the urban environment caused by changes in surface roughness result in the development of deeper clouds upstream of the urban center. Removal of the urban environment results in more vigorous vertical motion at the terrain interface and stronger orographic effects. This resulted in a westward shift in precipitation with the urban environment removed.