Evaluation of Urban Heat Stress Response to Heatwaves in the Washington, DC Metro Area Using UrbanNet Observations

The intensity, frequency, and duration of extreme weather events, such as heatwaves, are projected to rise with global warming and associated climate change. In urban areas, the urban heat island (UHI) effect may exacerbate these conditions further; however, its impact on heat stress remains uncertain. In this study, we explore the potential of using observations from NOAA/ARL’s UrbanNet to assess the impact of heatwave events on heat stress. UrbanNet is an advanced urban climate and meteorology monitoring network being established in the Washington, DC metro area with the aim of better characterizing the urban environment and supporting NOAA/ARL’s Urban GHG Emissions Measurement and Monitoring System (Urban-GEMMS) for greenhouse gas monitoring and modeling efforts. UrbanNet succeeds DCNet, which was established in 2002 in response to the events of 9/11. Originally, it was designed to provide real-time meteorological data over the greater DC area to support numerical weather prediction models and to provide the driving meteorological observations for atmospheric transport and dispersion models for emergency response applications. This network primarily measured wind speed, wind direction, air temperature, relative humidity, and high-frequency measurements of wind components and temperature across fifteen locations in the Washington, DC metro area.

Since early 2023, DCNet has been revitalized and renamed UrbanNet to reflect its evolving mission and potential expansion to other urban areas. In addition to the existing meteorological observations, the upgraded measurements now include atmospheric pressure, incoming and outgoing shortwave and longwave radiation, infrared temperature, precipitation, black globe temperature, as well as vertical profiles of wind components and boundary layer height. The temporal variability of heat stress over four UrbanNet sites was assessed using wet bulb globe temperature (WBGT) and compared with other estimated heat indices, including the heat index (HI) and humidex (HD). To assess heat stress patterns, we compared thresholds of heat indices with heatwave events identified by daily maximum air temperature thresholds. The analysis also included pre-existing DCNet observations from multiple locations in the Washington, DC area since 2003 to examine the frequency and trends, if any, of heatwaves and associated heat stress, and to evaluate their impact on the intensity of UHIs in these locations.