A Multiscalar Thermal Analysis of Urban Playgrounds

The ways in which many playgrounds and parks are designed are not conducive for thermally safe and active play by children. Children are more sensitive and vulnerable to heat-related illnesses than the average adult, mainly due to their small body mass-to-surface-area ratio. This results in thermoregulatory difficulties during physical activity in the warm-hot ambient temperatures. Notably, the mean radiant temperature influences surface temperatures of playground equipment, and hence the dangers of burns and heat stress are present, particularly in predominantly sunny climates. Impacts are important to understand due to current and future urban heating and climate effects, urban land use change, growth of urban areas, and a lack of bioclimatic design in warming cities. Urban climate models cannot resolve human-scale or playground-scale effects, and remote sensing (RS) data, although better, also misses subgrid variability that occurs on the scale of centimeters within a playground. The objective of this study is to address ‘touch-scale' (hand based) surface temperatures on the order of centimeters, assessing the variability within the various subgrids in order to develop a framework linking the three scales of data. We utilize two sets of surface temperature data collected mid-day in Phoenix Arizona: 1) MASTER (MODIS/ASTER) overflight RS data at a 7m resolution, and 2) in-situ touch-scale data at < 1cm resolution using infrared thermometry. Within Phoenix—the U.S. metropolitan area with the highest summer temperatures—select neighborhood data is focused on two playgrounds within one neighborhood from July 2011 and Sept 2014 (air temperatures of 38oC). Within-grid variability is assessed to determine the distribution of surface temperatures above or below the mean of remotely sensed data. Results demonstrate the RS MASTER data for the neighborhood and two parks generally fitting a normal distribution curve, while the touch-scale data has a positive, or right, skew to the higher temperatures due to the presence of materials with high thermal conductivity (metal and plastic slides, metal bars, plastic seats, rubber or artificial turf). These touch-scale values were 20–40oC greater than the 7m grid mean from the RS data within the playgrounds, reaching maximum magnitudes of 72–87oC (dark slides, rubber surfaces); under shade however, these surfaces were 23–38oC cooler. This study demonstrates that for select surfaces, RS data is sufficient (e.g., roads, roofs, parking lots); however, in playgrounds and other neighborhood locations, this resolution is not accurate enough to quantify extreme and dangerous temperatures. Touch-scale measurements were largely different than remotely sensed temperatures in the playgrounds, yet nearly identical for sand and concrete surfaces. This information provides a paradigm for linking point measurements with RS grid measurements, and a quantitative framework addressed various scales in urban climate research. Applying information to public safety and children's health, illness and injury due to extreme heat can be avoided, and playgrounds can be designed for thermally safe and active play.