Session Overview
PLENARY2: Plenary session II: Influence of cities on thunderstorms, clouds, and precipitation
Wednesday, 22/Jul/2015:
8:30am - 9:30am

Session Chair: Dev Niyogi, Purdue University
Location: St-Exupéry Amphitheater


Influence of cities on thunderstorms, clouds, and precipitation

Robert {"Bob"} D. Bornstein

San Jose State University, United States of America

Urban areas impact summer thunderstorms through a variety of direct and indirect dynamic, thermodynamic, and cloud microphysical processes, which can result in either new-storm initiation or the splitting of existing moving storms. These processes can increase or decrease precipitation amounts over and around urban areas, as well as impact their timing, location, and intensity. This presentation thus first reviews the literature on the relative roles of urban dynamics and aerosols on summer thunderstorms. It then summarizes uncertainties in our current understanding of these processes, including specific causal mechanisms/processes that produce splitting, geographical and climatological impacts, seasonal variations, urban parametrizations and data requirements for urban mesoscale models, and impact forecasts (e.g., for flash floods). It finally proposes a process whereby “golden” case studies could be selected for model inter-comparisons that could clarify these uncertainties. This latter process could include: (a) formation of a coordinating committee to oversee the exercise, (b) establishment of criteria for submission of potential case studies (i.e., documentation of urban impacts, and descriptions of available surface and PBL data sets), (c) procedures for case study selection, and (d) development of inter-comparison procedures.