Heat and Cold Roses of U.S. Cities: a New Tool for Optimizing Urban Climate

Thermal comfort in cities is influenced not only by air temperature but also by the shortwave and longwave radiation environment, and wind velocity. Increasing ventilation has been demonstrated to improve thermal comfort during hot weather conditions in cities. However, during cold conditions increased ventilation lowers thermal comfort. In the context of urban design for climate adaptation, it is desirable to know from which directions hot and cold weather conditions approach the city. For this purpose we present a simple extension to the conventional “wind rose” concept. This tool, which we refer to as ‘heat and cold roses’, visualizes the wind direction statistics in combination with hot and cold weather conditions. We demonstrate that for a multitude of cities in the U.S. the main directions of hot and cold weather conditions do not overlap. In analyzing the heat and cold weather roses from the 50 largest U.S. cities, two distinct typologies of heat and cold roses are identified. The implications and potential for using these typologies for developing improved building configuration designs is demonstrated by microscale bioclimatic simulations. The studied, hypothetical building design configuration improved thermal comfort for both hot and cold conditions.