TY - JOUR
T1 - Micrometeorological determinants of pedestrian thermal exposure during record-breaking heat in Tempe, Arizona
T2 - Introducing the MaRTy observational platform
AU - Middel, Ariane
AU - Krayenhoff, E. Scott
N1 - Funding Information:
This research was sponsored by University of Kaiserslautern , grant “Microclimate Data Collection, Analysis, and Visualization”, the US National Science Foundation (NSF) under grants SES-1520803 , CBET-1444758 and CMMI-1635490 (Urban Water Innovation Network), and a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the sponsoring organizations. The authors thank Jennifer Vanos and David Sailor for assisting with design of the MaRTy platform.
Publisher Copyright:
© 2019 The Authors
PY - 2019/10/15
Y1 - 2019/10/15
N2 - We report the first set of urban micrometeorological measurements for assessment of pedestrian thermal exposure during extreme heat in a dry climate. Hourly measurements of air temperature, humidity, wind speed and six-directional shortwave and longwave radiation were recorded with a mobile human-biometeorological station (MaRTy) from 10:00 to 21:00 local time, June 19, 2016, at 22 sites that include diverse microscale urban land cover. Sky view factor (SVF) and 360° pervious and impervious view factors for each location were calculated from six-directional fisheye photographs. Mean radiant temperature (TMRT) was determined using the six-directional method. Three-dimensional radiation budgets were decomposed into directional weighted shortwave and longwave radiation components to create a distinct TMRT profile for each site and determine the main drivers of TMRT and thermal exposure. Air temperature peaked locally at 48.5 °C, with a maximum TMRT of 76.4 °C at 15:00 MST in an east-west building canyon. Longwave radiation measured by laterally-oriented sensors dominated the TMRT budget, suggesting the importance of cooling vertical surfaces adjacent to pedestrians. Lateral shortwave radiation contributions were most spatially and temporally variable across TMRT profiles, reflecting the diverse shade conditions. The largest radiation fluxes contributing to TMRT were particularly sensitive to shade and secondarily to ground cover. Trees reduced afternoon TMRT up to 33.4 °C but exhibited a clear TMRT increase of up to 5 °C after sunset; during daytime, trees generated ground cover-dependent longwave radiant cooling or warming. Replacement of impervious with pervious ground cover cooled TMRT at all measurement times, even under dense tree shade. While recent work has found that adaptation cannot offset projected urban air temperature increases, outdoor thermal exposure depends on additional micrometeorological variables, including shortwave and longwave radiation, indicating the need and the opportunity to create pedestrian spaces that are radiantly cool within the context of future urban heat.
AB - We report the first set of urban micrometeorological measurements for assessment of pedestrian thermal exposure during extreme heat in a dry climate. Hourly measurements of air temperature, humidity, wind speed and six-directional shortwave and longwave radiation were recorded with a mobile human-biometeorological station (MaRTy) from 10:00 to 21:00 local time, June 19, 2016, at 22 sites that include diverse microscale urban land cover. Sky view factor (SVF) and 360° pervious and impervious view factors for each location were calculated from six-directional fisheye photographs. Mean radiant temperature (TMRT) was determined using the six-directional method. Three-dimensional radiation budgets were decomposed into directional weighted shortwave and longwave radiation components to create a distinct TMRT profile for each site and determine the main drivers of TMRT and thermal exposure. Air temperature peaked locally at 48.5 °C, with a maximum TMRT of 76.4 °C at 15:00 MST in an east-west building canyon. Longwave radiation measured by laterally-oriented sensors dominated the TMRT budget, suggesting the importance of cooling vertical surfaces adjacent to pedestrians. Lateral shortwave radiation contributions were most spatially and temporally variable across TMRT profiles, reflecting the diverse shade conditions. The largest radiation fluxes contributing to TMRT were particularly sensitive to shade and secondarily to ground cover. Trees reduced afternoon TMRT up to 33.4 °C but exhibited a clear TMRT increase of up to 5 °C after sunset; during daytime, trees generated ground cover-dependent longwave radiant cooling or warming. Replacement of impervious with pervious ground cover cooled TMRT at all measurement times, even under dense tree shade. While recent work has found that adaptation cannot offset projected urban air temperature increases, outdoor thermal exposure depends on additional micrometeorological variables, including shortwave and longwave radiation, indicating the need and the opportunity to create pedestrian spaces that are radiantly cool within the context of future urban heat.
KW - Extreme heat
KW - MaRTy
KW - Mean radiant temperature
KW - Microscale Urban Design
KW - Radiation budget decomposition
KW - Thermal comfort
UR - http://www.scopus.com/inward/record.url?scp=85067175555&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85067175555&partnerID=8YFLogxK
U2 - 10.1016/j.scitotenv.2019.06.085
DO - 10.1016/j.scitotenv.2019.06.085
M3 - Article
C2 - 31207504
AN - SCOPUS:85067175555
SN - 0048-9697
VL - 687
SP - 137
EP - 151
JO - Science of the Total Environment
JF - Science of the Total Environment
ER -