Thermal Comfort and Extreme Heat: A Summertime Assessment of RayMan Model Sensitivity in Downtown Tempe, AZ

Climate change projections and population trends for the desert Southwestern United States are likely to exacerbate already stressed urban ecosystems as temperatures and population numbers increase. Future planning to address these issues requires better information and tools (models) to help design sustainable downtowns. Tempe, AZ, located within the Greater Phoenix Metropolitan area, has served as laboratory for a number of human comfort related studies (i.e. people's perceptions, environmental effects from solar panels and inside cars, microclimate effects). Some of these previous studies used RayMan as a means to quantify thermal comfort conditions based on meteorological variables and fish eye photos. The purpose of our study is to assess Rayman model performance by investigating model sensitivity to key inputs (mean radiant, surface and air temperature, relative humidity, wind speed and albedo) and how those variables impact thermal comfort outcomes. On June 20th, 2015, we collected weather observations, thermographic imagery and albedo values every three hours at selected locations in downtown Tempe, AZ using a Kestrel 4400 heat stress tracker, a FLIR E4 infrared camera and a ASD Field Spec-4 Wide-Res spectometer. We used a piece wise approach progressing from the minimum required inputs to the complete set of our observations to assess the relative importance of various input variables. By exploring model sensitivity and the effects on thermal comfort, we shed light on the importance of model inputs and representation of thermal conditions in urban areas. Such knowledge is necessary to help guide sustainable designs for current and future downtowns.